- 18 May, 2020 3 commits
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Sam Bobroff authored
EEH device state is currently removed (by eeh_remove_device()) during the device release handler, which is invoked as the device's reference count drops to zero. This may take some time, or forever, as other threads may hold references. However, the PCI device state is released synchronously by pci_stop_and_remove_bus_device(). This mismatch causes problems, for example the device may be re-discovered as a new device before the release handler has been called, leaving the PCI and EEH state mismatched. So instead, call eeh_remove_device() from the bus device removal handlers, which are called synchronously in the removal path. Signed-off-by:
Sam Bobroff <sbobroff@linux.ibm.com> Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/0a1f5105d3a33b1c090bba31de63eb0cdd25de7b.1588045502.git.sbobroff@linux.ibm.com
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Sam Bobroff authored
If a device is hot unplgged during EEH recovery, it's possible for the RTAS call to ibm,configure-pe in pseries_eeh_configure() to return parameter error (-3), however negative return values are not checked for and this leads to an infinite loop. Fix this by correctly bailing out on negative values. Signed-off-by:
Nathan Lynch <nathanl@linux.ibm.com> Link: https://lore.kernel.org/r/1b0a6010a647dc915816e44845b64d72066676a7.1588045502.git.sbobroff@linux.ibm.com
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Michael Ellerman authored
Currently we don't report anything useful in /proc/<pid>/status: $ grep Speculation_Store_Bypass /proc/self/status Speculation_Store_Bypass: unknown Our mitigation is currently always a barrier instruction, which doesn't map that well onto the existing possibilities for the PR_SPEC values. However even if we added a "barrier" type PR_SPEC value, userspace would still need to consult some other source to work out which type of barrier to use. So reporting "vulnerable" seems sufficient, as userspace can see that and then consult its source to determine what barrier to use. Signed-off-by:
Gustavo Walbon <gwalbon@linux.ibm.com> Signed-off-by:
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- 15 May, 2020 10 commits
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Michael Ellerman authored
create_cpu_loop() calls smu_sat_get_sdb_partition() which does kmalloc() and returns the allocated buffer. In fact it's called twice, and neither buffer is freed. This results in a memory leak as reported by Erhard: unreferenced object 0xc00000047081f840 (size 32): comm "kwindfarm", pid 203, jiffies 4294880630 (age 5552.877s) hex dump (first 32 bytes): c8 06 02 7f ff 02 ff 01 fb bf 00 41 00 20 00 00 ...........A. .. 00 07 89 37 00 a0 00 00 00 00 00 00 00 00 00 00 ...7............ backtrace: [<0000000083f0a65c>] .smu_sat_get_sdb_partition+0xc4/0x2d0 [windfarm_smu_sat] [<000000003010fcb7>] .pm112_wf_notify+0x104c/0x13bc [windfarm_pm112] [<00000000b958b2dd>] .notifier_call_chain+0xa8/0x180 [<0000000070490868>] .blocking_notifier_call_chain+0x64/0x90 [<00000000131d8149>] .wf_thread_func+0x114/0x1a0 [<000000000d54838d>] .kthread+0x13c/0x190 [<00000000669b72bc>] .ret_from_kernel_thread+0x58/0x64 unreferenced object 0xc0000004737089f0 (size 16): comm "kwindfarm", pid 203, jiffies 4294880879 (age 5552.050s) hex dump (first 16 bytes): c4 04 01 7f 22 11 e0 e6 ff 55 7b 12 ec 11 00 00 ...."....U{..... backtrace: [<0000000083f0a65c>] .smu_sat_get_sdb_partition+0xc4/0x2d0 [windfarm_smu_sat] [<00000000b94ef7e1>] .pm112_wf_notify+0x1294/0x13bc [windfarm_pm112] [<00000000b958b2dd>] .notifier_call_chain+0xa8/0x180 [<0000000070490868>] .blocking_notifier_call_chain+0x64/0x90 [<00000000131d8149>] .wf_thread_func+0x114/0x1a0 [<000000000d54838d>] .kthread+0x13c/0x190 [<00000000669b72bc>] .ret_from_kernel_thread+0x58/0x64 Fix it by rearranging the logic so we deal with each buffer separately, which then makes it easy to free the buffer once we're done with it. Fixes: ac171c46 ("[PATCH] powerpc: Thermal control for dual core G5s") Cc: stable@vger.kernel.org # v2.6.16+ Reported-by:Erhard F. <erhard_f@mailbox.org> Signed-off-by:
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Michael Ellerman authored
This is based on the count_instructions test. However this one also counts the number of failed stcx's, and in conjunction with knowing the size of the stcx loop, can calculate the total number of instructions executed even in the face of non-deterministic stcx failures. Signed-off-by:
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Michael Ellerman authored
There's no need to cast in task_pt_regs() as tsk->thread.regs should already be a struct pt_regs. If someone's using task_pt_regs() on something that's not a task but happens to have a thread.regs then we'll deal with them later. Signed-off-by:
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Michael Ellerman authored
Aneesh increased the size of struct pt_regs by 16 bytes and started seeing this WARN_ON: smp: Bringing up secondary CPUs ... ------------[ cut here ]------------ WARNING: CPU: 0 PID: 0 at arch/powerpc/kernel/process.c:455 giveup_all+0xb4/0x110 Modules linked in: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.7.0-rc2-gcc-8.2.0-1.g8f6a41f-default+ #318 NIP: c00000000001a2b4 LR: c00000000001a29c CTR: c0000000031d0000 REGS: c0000000026d3980 TRAP: 0700 Not tainted (5.7.0-rc2-gcc-8.2.0-1.g8f6a41f-default+) MSR: 800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 48048224 XER: 00000000 CFAR: c000000000019cc8 IRQMASK: 1 GPR00: c00000000001a264 c0000000026d3c20 c0000000026d7200 800000000280b033 GPR04: 0000000000000001 0000000000000000 0000000000000077 30206d7372203164 GPR08: 0000000000002000 0000000002002000 800000000280b033 3230303030303030 GPR12: 0000000000008800 c0000000031d0000 0000000000800050 0000000002000066 GPR16: 000000000309a1a0 000000000309a4b0 000000000309a2d8 000000000309a890 GPR20: 00000000030d0098 c00000000264da40 00000000fd620000 c0000000ff798080 GPR24: c00000000264edf0 c0000001007469f0 00000000fd620000 c0000000020e5e90 GPR28: c00000000264edf0 c00000000264d200 000000001db60000 c00000000264d200 NIP [c00000000001a2b4] giveup_all+0xb4/0x110 LR [c00000000001a29c] giveup_all+0x9c/0x110 Call Trace: [c0000000026d3c20] [c00000000001a264] giveup_all+0x64/0x110 (unreliable) [c0000000026d3c90] [c00000000001ae34] __switch_to+0x104/0x480 [c0000000026d3cf0] [c000000000e0b8a0] __schedule+0x320/0x970 [c0000000026d3dd0] [c000000000e0c518] schedule_idle+0x38/0x70 [c0000000026d3df0] [c00000000019c7c8] do_idle+0x248/0x3f0 [c0000000026d3e70] [c00000000019cbb8] cpu_startup_entry+0x38/0x40 [c0000000026d3ea0] [c000000000011bb0] rest_init+0xe0/0xf8 [c0000000026d3ed0] [c000000002004820] start_kernel+0x990/0x9e0 [c0000000026d3f90] [c00000000000c49c] start_here_common+0x1c/0x400 Which was unexpected. The warning is checking the thread.regs->msr value of the task we are switching from: usermsr = tsk->thread.regs->msr; ... WARN_ON((usermsr & MSR_VSX) && !((usermsr & MSR_FP) && (usermsr & MSR_VEC))); ie. if MSR_VSX is set then both of MSR_FP and MSR_VEC are also set. Dumping tsk->thread.regs->msr we see that it's: 0x1db60000 Which is not a normal looking MSR, in fact the only valid bit is MSR_VSX, all the other bits are reserved in the current definition of the MSR. We can see from the oops that it was swapper/0 that we were switching from when we hit the warning, ie. init_task. So its thread.regs points to the base (high addresses) in init_stack. Dumping the content of init_task->thread.regs, with the members of pt_regs annotated (the 16 bytes larger version), we see: 0000000000000000 c000000002780080 gpr[0] gpr[1] 0000000000000000 c000000002666008 gpr[2] gpr[3] c0000000026d3ed0 0000000000000078 gpr[4] gpr[5] c000000000011b68 c000000002780080 gpr[6] gpr[7] 0000000000000000 0000000000000000 gpr[8] gpr[9] c0000000026d3f90 0000800000002200 gpr[10] gpr[11] c000000002004820 c0000000026d7200 gpr[12] gpr[13] 000000001db60000 c0000000010aabe8 gpr[14] gpr[15] c0000000010aabe8 c0000000010aabe8 gpr[16] gpr[17] c00000000294d598 0000000000000000 gpr[18] gpr[19] 0000000000000000 0000000000001ff8 gpr[20] gpr[21] 0000000000000000 c00000000206d608 gpr[22] gpr[23] c00000000278e0cc 0000000000000000 gpr[24] gpr[25] 000000002fff0000 c000000000000000 gpr[26] gpr[27] 0000000002000000 0000000000000028 gpr[28] gpr[29] 000000001db60000 0000000004750000 gpr[30] gpr[31] 0000000002000000 000000001db60000 nip msr 0000000000000000 0000000000000000 orig_r3 ctr c00000000000c49c 0000000000000000 link xer 0000000000000000 0000000000000000 ccr softe 0000000000000000 0000000000000000 trap dar 0000000000000000 0000000000000000 dsisr result 0000000000000000 0000000000000000 ppr kuap 0000000000000000 0000000000000000 pad[2] pad[3] This looks suspiciously like stack frames, not a pt_regs. If we look closely we can see return addresses from the stack trace above, c000000002004820 (start_kernel) and c00000000000c49c (start_here_common). init_task->thread.regs is setup at build time in processor.h: #define INIT_THREAD { \ .ksp = INIT_SP, \ .regs = (struct pt_regs *)INIT_SP - 1, /* XXX bogus, I think */ \ The early boot code where we setup the initial stack is: LOAD_REG_ADDR(r3,init_thread_union) /* set up a stack pointer */ LOAD_REG_IMMEDIATE(r1,THREAD_SIZE) add r1,r3,r1 li r0,0 stdu r0,-STACK_FRAME_OVERHEAD(r1) Which creates a stack frame of size 112 bytes (STACK_FRAME_OVERHEAD). Which is far too small to contain a pt_regs. So the result is init_task->thread.regs is pointing at some stack frames on the init stack, not at a pt_regs. We have gotten away with this for so long because with pt_regs at its current size the MSR happens to point into the first frame, at a location that is not written to by the early asm. With the 16 byte expansion the MSR falls into the second frame, which is used by the compiler, and collides with a saved register that tends to be non-zero. As far as I can see this has been wrong since the original merge of 64-bit ppc support, back in 2002. Conceptually swapper should have no regs, it never entered from userspace, and in fact that's what we do on 32-bit. It's also presumably what the "bogus" comment is referring to. So I think the right fix is to just not-initialise regs at all. I'm slightly worried this will break some code that isn't prepared for a NULL regs, but we'll have to see. Remove the comment in head_64.S which refers to us setting up the regs (even though we never did), and is otherwise not really accurate any more. Reported-by:Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Signed-off-by:
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Gustavo A. R. Silva authored
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by:Gustavo A. R. Silva <gustavoars@kernel.org> Signed-off-by:
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Gustavo A. R. Silva authored
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: -
Nicholas Piggin authored
It's not very nice to zero trap for this, because then system calls no longer have trap_is_syscall(regs) invariant, and we can't distinguish between sc and scv system calls (in a later patch). Take one last unused bit from the low bits of the pt_regs.trap word for this instead. There is not a really good reason why it should be in trap as opposed to another field, but trap has some concept of flags and it exists. Ideally I think we would move trap to 2-byte field and have 2 more bytes available independently. Add a selftests case for this, which can be seen to fail if trap_norestart() is changed to return false. Signed-off-by:
Nicholas Piggin <npiggin@gmail.com> [mpe: Make them static inlines] Signed-off-by:
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Nicholas Piggin authored
A new system call interrupt will be added with a new trap number. Hide the explicit 0xc00 test behind an accessor to reduce churn in callers. Signed-off-by:
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Nicholas Piggin authored
The pt_regs.trap field keeps 4 low bits for some metadata about the trap or how it was handled, which is masked off in order to test the architectural trap number. Add a set_trap() accessor to set this, equivalent to TRAP() for returning it. This is actually not quite the equivalent of TRAP() because it always clears the low bits, which may be harmless if it can only be updated via ptrace syscall, but it seems dangerous. In fact settting TRAP from ptrace doesn't seem like a great idea so maybe it's better deleted. Signed-off-by:
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Nicholas Piggin authored
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- 11 May, 2020 10 commits
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Christophe Leroy authored
When CONFIG_KASAN is selected, the stack usage is increased. In the same way as x86 and arm64 architectures, increase THREAD_SHIFT when CONFIG_KASAN is selected. Fixes: 2edb16ef ("powerpc/32: Add KASAN support") Reported-by: <erhard_f@mailbox.org> Signed-off-by:
Christophe Leroy <christophe.leroy@c-s.fr> Signed-off-by:
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Christophe Leroy authored
These three powerpc macros have been replaced by equivalent generic macros and are not used anymore. Remove them. Signed-off-by:
Joel Stanley <joel@jms.id.au> Signed-off-by:
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Christophe Leroy authored
_ALIGN() is specific to powerpc ALIGN() is generic and does the same Replace _ALIGN() by ALIGN() Signed-off-by:
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Christophe Leroy authored
_ALIGN_UP() is specific to powerpc ALIGN() is generic and does the same Replace _ALIGN_UP() by ALIGN() Signed-off-by:
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Christophe Leroy authored
_ALIGN_DOWN() is specific to powerpc ALIGN_DOWN() is generic and does the same Replace _ALIGN_DOWN() by ALIGN_DOWN() Signed-off-by:
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Christophe Leroy authored
_ALIGN_UP() is specific to powerpc ALIGN() is generic and does the same Replace _ALIGN_UP() by ALIGN() Signed-off-by:
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Christophe Leroy authored
Since 01 May 2020, our email adresses have changed to @csgroup.eu Update MAINTAINERS accordingly. Signed-off-by:
Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by:
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Wolfram Sang authored
My 'pengutronix' address is defunct for years. Merge the entries and use the proper contact address. Signed-off-by:
Wolfram Sang <wsa@kernel.org> Signed-off-by:
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Andrey Abramov authored
Replace relaswap with built-in one, because relaswap does a simple byte to byte swap. Since Spectre mitigations have made indirect function calls more expensive, and the default simple byte copies swap is implemented without them, an "optimized" custom swap function is now a waste of time as well as code. Signed-off-by:
Andrey Abramov <st5pub@yandex.ru> Reviewed-by:
George Spelvin <lkml@sdf.org> Signed-off-by:
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Christophe JAILLET authored
Fix a cut'n'paste error in a warning message. This should be 'cpu-idle-state-residency-ns' to match the property searched in the previous 'of_property_read_u32_array()' Fixes: 9c7b185a ("powernv/cpuidle: Parse dt idle properties into global structure") Signed-off-by:
Christophe JAILLET <christophe.jaillet@wanadoo.fr> Reviewed-by:
Gautham R. Shenoy <ego@linux.vnet.ibm.com> Signed-off-by:
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- 06 May, 2020 1 commit
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Michael Ellerman authored
This merges the lockless page table walk rework series from Aneesh. Because it touches powerpc KVM code we are sharing it with the kvm-ppc tree in our topic/ppc-kvm branch. This is the cover letter from Aneesh: Avoid IPI while updating page table entries. Problem Summary: Slow termination of KVM guest with large guest RAM config due to a large number of IPIs that were caused by clearing level 1 PTE entries (THP) entries. This is shown in the stack trace below. - qemu-system-ppc [kernel.vmlinux] [k] smp_call_function_many - smp_call_function_many - 36.09% smp_call_function_many serialize_against_pte_lookup radix__pmdp_huge_get_and_clear zap_huge_pmd unmap_page_range unmap_vmas unmap_region __do_munmap __vm_munmap sys_munmap system_call __munmap qemu_ram_munmap qemu_anon_ram_free reclaim_ramblock call_rcu_thread qemu_thread_start start_thread __clone Why we need to do IPI when clearing PMD entries: This was added as part of commit: 13bd817b ("powerpc/thp: Serialize pmd clear against a linux page table walk") serialize_against_pte_lookup makes sure that all parallel lockless page table walk completes before we convert a PMD pte entry to regular pmd entry. We end up doing that conversion in the below scenarios 1) __split_huge_zero_page_pmd 2) do_huge_pmd_wp_page_fallback 3) MADV_DONTNEED running parallel to page faults. local_irq_disable and lockless page table walk: The lockless page table walk work with the assumption that we can dereference the page table contents without holding a lock. For this to work, we need to make sure we read the page table contents atomically and page table pages are not going to be freed/released while we are walking the table pages. We can achieve by using a rcu based freeing for page table pages or if the architecture implements broadcast tlbie, we can block the IPI as we walk the page table pages. To support both the above framework, lockless page table walk is done with irq disabled instead of rcu_read_lock() We do have two interface for lockless page table walk, gup fast and __find_linux_pte. This patch series makes __find_linux_pte table walk safe against the conversion of PMD PTE to regular PMD. gup fast: gup fast is already safe against THP split because kernel now differentiate between a pmd split and a compound page split. gup fast can run parallel to a pmd split and we prevent a parallel gup fast to a hugepage split, by freezing the page refcount and failing the speculative page ref increment. Similar to how gup is safe against parallel pmd split, this patch series updates the __find_linux_pte callers to be safe against a parallel pmd split. We do that by enforcing the following rules. 1) Don't reload the pte value, because that can be updated in parallel. 2) Code should be able to work with a stale PTE value and not the recent one. ie, the pte value that we are looking at may not be the latest value in the page table. 3) Before looking at pte value check for _PAGE_PTE bit. We now do this as part of pte_present() check. Performance: This speeds up Qemu guest RAM del/unplug time as below 128 core, 496GB guest: Without patch: munmap start: timer = 13162 ms, PID=7684 munmap finish: timer = 95312 ms, PID=7684 - delta = 82150 ms With patch (upto removing IPI) munmap start: timer = 196449 ms, PID=6681 munmap finish: timer = 196488 ms, PID=6681 - delta = 39ms With patch (with adding the tlb invalidate in pmdp_huge_get_and_clear_full) munmap start: timer = 196345 ms, PID=6879 munmap finish: timer = 196714 ms, PID=6879 - delta = 369ms Link: https://lore.kernel.org/r/20200505071729.54912-1-aneesh.kumar@linux.ibm.com
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- 05 May, 2020 16 commits
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Aneesh Kumar K.V authored
MADV_DONTNEED holds mmap_sem in read mode and that implies a parallel page fault is possible and the kernel can end up with a level 1 PTE entry (THP entry) converted to a level 0 PTE entry without flushing the THP TLB entry. Most architectures including POWER have issues with kernel instantiating a level 0 PTE entry while holding level 1 TLB entries. The code sequence I am looking at is down_read(mmap_sem) down_read(mmap_sem) zap_pmd_range() zap_huge_pmd() pmd lock held pmd_cleared table details added to mmu_gather pmd_unlock() insert a level 0 PTE entry() tlb_finish_mmu(). Fix this by forcing a tlb flush before releasing pmd lock if this is not a fullmm invalidate. We can safely skip this invalidate for task exit case (fullmm invalidate) because in that case we are sure there can be no parallel fault handlers. This do change the Qemu guest RAM del/unplug time as below 128 core, 496GB guest: Without patch: munmap start: timer = 196449 ms, PID=6681 munmap finish: timer = 196488 ms, PID=6681 - delta = 39ms With patch: munmap start: timer = 196345 ms, PID=6879 munmap finish: timer = 196714 ms, PID=6879 - delta = 369ms Signed-off-by: -
Aneesh Kumar K.V authored
Now that all the lockless page table walk is careful w.r.t the PTE address returned, we can now revert commit: 13bd817b ("powerpc/thp: Serialize pmd clear against a linux page table walk.") We also drop the equivalent IPI from other pte updates routines. We still keep IPI in hash pmdp collapse and that is to take care of parallel hash page table insert. The radix pmdp collapse flush can possibly be removed once I am sure generic code doesn't have the any expectations around parallel gup walk. This speeds up Qemu guest RAM del/unplug time as below 128 core, 496GB guest: Without patch: munmap start: timer = 13162 ms, PID=7684 munmap finish: timer = 95312 ms, PID=7684 - delta = 82150 ms With patch: munmap start: timer = 196449 ms, PID=6681 munmap finish: timer = 196488 ms, PID=6681 - delta = 39ms Signed-off-by:
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Aneesh Kumar K.V authored
This adds _PAGE_PTE check and makes sure we validate the pte value returned via find_kvm_host_pte. NOTE: this also considers _PAGE_INVALID to the software valid bit. Signed-off-by:
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Aneesh Kumar K.V authored
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Aneesh Kumar K.V authored
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Aneesh Kumar K.V authored
We now depend on kvm->mmu_lock Signed-off-by:
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Aneesh Kumar K.V authored
Current code just hold rmap lock to ensure parallel page table update is prevented. That is not sufficient. The kernel should also check whether a mmu_notifer callback was running in parallel. Signed-off-by:
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Aneesh Kumar K.V authored
Since kvmppc_do_h_enter can get called in realmode use low level arch_spin_lock which is safe to be called in realmode. Signed-off-by:
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Aneesh Kumar K.V authored
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Aneesh Kumar K.V authored
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Aneesh Kumar K.V authored
update kvmppc_hv_handle_set_rc to use find_kvm_nested_guest_pte and find_kvm_secondary_pte Signed-off-by:
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Aneesh Kumar K.V authored
The locking rules for walking nested shadow linux page table is different from process scoped table. Hence add a helper for nested page table walk and also add check whether we are holding the right locks. Signed-off-by:
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Aneesh Kumar K.V authored
The locking rules for walking partition scoped table is different from process scoped table. Hence add a helper for secondary linux page table walk and also add check whether we are holding the right locks. Signed-off-by:
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Aneesh Kumar K.V authored
These functions can get called in realmode. Hence use low level arch_spin_lock which is safe to be called in realmode. Signed-off-by:
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Aneesh Kumar K.V authored
read_user_stack_slow is called with interrupts soft disabled and it copies contents from the page which we find mapped to a specific address. To convert userspace address to pfn, the kernel now uses lockless page table walk. The kernel needs to make sure the pfn value read remains stable and is not released and reused for another process while the contents are read from the page. This can only be achieved by holding a page reference. One of the first approaches I tried was to check the pte value after the kernel copies the contents from the page. But as shown below we can still get it wrong CPU0 CPU1 pte = READ_ONCE(*ptep); pte_clear(pte); put_page(page); page = alloc_page(); memcpy(page_address(page), "secret password", nr); memcpy(buf, kaddr + offset, nb); put_page(page); handle_mm_fault() page = alloc_page(); set_pte(pte, page); if (pte_val(pte) != pte_val(*ptep)) Hence switch to __get_user_pages_fast. Signed-off-by: -
Aneesh Kumar K.V authored
A lockless page table walk should be safe against parallel THP collapse, THP split and madvise(MADV_DONTNEED)/parallel fault. This patch makes sure kernel won't reload the pteval when checking for different conditions. The patch also added a check for pte_present to make sure the kernel is indeed operating on a PTE and not a pointer to level 0 table page. The pfn value we find here can be different from the actual pfn on which machine check happened. This can happen if we raced with a parallel update of the page table. In such a scenario we end up isolating a wrong pfn. But that doesn't have any other side effect. Signed-off-by:
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