- 04 Feb, 2021 40 commits
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Sean Christopherson authored
Add a helper to generate the mask of reserved PA bits in the host. No functional change intended. Signed-off-by:
Sean Christopherson <seanjc@google.com> Message-Id: <20210204000117.3303214-10-seanjc@google.com> Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com>
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Sean Christopherson authored
Use reserved_gpa_bits, which accounts for exceptions to the maxphyaddr rule, e.g. SEV's C-bit, for the page {table,directory,etc...} entry (PxE) reserved bits checks. For SEV, the C-bit is ignored by hardware when walking pages tables, e.g. the APM states: Note that while the guest may choose to set the C-bit explicitly on instruction pages and page table addresses, the value of this bit is a don't-care in such situations as hardware always performs these as private accesses. Such behavior is expected to hold true for other features that repurpose GPA bits, e.g. KVM could theoretically emulate SME or MKTME, which both allow non-zero repurposed bits in the page tables. Conceptually, KVM should apply reserved GPA checks universally, and any features that do not adhere to the basic rule should be explicitly handled, i.e. if a GPA bit is repurposed but not allowed in page tables for whatever reason. Refactor __reset_rsvds_bits_mask() to take the pre-generated reserved bits mask, and opportunistically clean up its code, e.g. to align lines and comments. Practically speaking, this is change is a likely a glorified nop given the current KVM code base. SEV's C-bit is the only repurposed GPA bit, and KVM doesn't support shadowing encrypted page tables (which is theoretically possible via SEV debug APIs). Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Signed-off-by: -
Sean Christopherson authored
Rename cr3_lm_rsvd_bits to reserved_gpa_bits, and use it for all GPA legality checks. AMD's APM states: If the C-bit is an address bit, this bit is masked from the guest physical address when it is translated through the nested page tables. Thus, any access that can conceivably be run through NPT should ignore the C-bit when checking for validity. For features that KVM emulates in software, e.g. MTRRs, there is no clear direction in the APM for how the C-bit should be handled. For such cases, follow the SME behavior inasmuch as possible, since SEV is is essentially a VM-specific variant of SME. For SME, the APM states: In this case the upper physical address bits are treated as reserved when the feature is enabled except where otherwise indicated. Collecting the various relavant SME snippets in the APM and cross- referencing the omissions with Linux kernel code, this leaves MTTRs and APIC_BASE as the only flows that KVM emulates that should _not_ ignore the C-bit. Note, this means the reserved bit checks in the page tables are technically broken. This will be remedied in a future patch. Although the page table checks are technically broken, in practice, it's all but guaranteed to be irrelevant. NPT is required for SEV, i.e. shadowing page tables isn't needed in the common case. Theoretically, the checks could be in play for nested NPT, but it's extremely unlikely that anyone is running nested VMs on SEV, as doing so would require L1 to expose sensitive data to L0, e.g. the entire VMCB. And if anyone is running nested VMs, L0 can't read the guest's encrypted memory, i.e. L1 would need to put its NPT in shared memory, in which case the C-bit will never be set. Or, L1 could use shadow paging, but again, if L0 needs to read page tables, e.g. to load PDPTRs, the memory can't be encrypted if L1 has any expectation of L0 doing the right thing. Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Brijesh Singh <brijesh.singh@amd.com> Signed-off-by:
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Sean Christopherson authored
Replace an open coded check for an invalid CR3 with its equivalent helper. No functional change intended. Signed-off-by:
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Sean Christopherson authored
Replace a variety of open coded GPA checks with the recently introduced common helpers. No functional change intended. Signed-off-by:
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Sean Christopherson authored
Add a helper to genericize checking for a legal GPA that also must conform to an arbitrary alignment, and use it in the existing page_address_valid(). Future patches will replace open coded variants in VMX and SVM. Signed-off-by:
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Sean Christopherson authored
Add a helper to check for a legal GPA, and use it to consolidate code in existing, related helpers. Future patches will extend usage to VMX and SVM code, properly handle exceptions to the maxphyaddr rule, and add more helpers. No functional change intended. Signed-off-by:
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Sean Christopherson authored
Don't clear the SME C-bit when reading a guest PDPTR, as the GPA (CR3) is in the guest domain. Barring a bizarre paravirtual use case, this is likely a benign bug. SME is not emulated by KVM, loading SEV guest PDPTRs is doomed as KVM can't use the correct key to read guest memory, and setting guest MAXPHYADDR higher than the host, i.e. overlapping the C-bit, would cause faults in the guest. Note, for SEV guests, stripping the C-bit is technically aligned with CPU behavior, but for KVM it's the greater of two evils. Because KVM doesn't have access to the guest's encryption key, ignoring the C-bit would at best result in KVM reading garbage. By keeping the C-bit, KVM will fail its read (unless userspace creates a memslot with the C-bit set). The guest will still undoubtedly die, as KVM will use '0' for the PDPTR value, but that's preferable to interpreting encrypted data as a PDPTR. Fixes: d0ec49d4 ("kvm/x86/svm: Support Secure Memory Encryption within KVM") Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Brijesh Singh <brijesh.singh@amd.com> Signed-off-by:
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Sean Christopherson authored
Set cr3_lm_rsvd_bits, which is effectively an invalid GPA mask, at vCPU reset. The reserved bits check needs to be done even if userspace never configures the guest's CPUID model. Cc: stable@vger.kernel.org Fixes: 0107973a ("KVM: x86: Introduce cr3_lm_rsvd_bits in kvm_vcpu_arch") Signed-off-by:
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David Woodhouse authored
Signed-off-by:David Woodhouse <dwmw@amazon.co.uk>
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David Woodhouse authored
Instead of adding a plethora of new KVM_CAP_XEN_FOO capabilities, just add bits to the return value of KVM_CAP_XEN_HVM. Signed-off-by: -
David Woodhouse authored
It turns out that we can't handle event channels *entirely* in userspace by delivering them as ExtINT, because KVM is a bit picky about when it accepts ExtINT interrupts from a legacy PIC. The in-kernel local APIC has to have LVT0 configured in APIC_MODE_EXTINT and unmasked, which isn't necessarily the case for Xen guests especially on secondary CPUs. To cope with this, add kvm_xen_get_interrupt() which checks the evtchn_pending_upcall field in the Xen vcpu_info, and delivers the Xen upcall vector (configured by KVM_XEN_ATTR_TYPE_UPCALL_VECTOR) if it's set regardless of LAPIC LVT0 configuration. This gives us the minimum support we need for completely userspace-based implementation of event channels. This does mean that vcpu_enter_guest() needs to check for the evtchn_pending_upcall flag being set, because it can't rely on someone having set KVM_REQ_EVENT unless we were to add some way for userspace to do so manually. Signed-off-by: -
Joao Martins authored
Allow the Xen emulated guest the ability to register secondary vcpu time information. On Xen guests this is used in order to be mapped to userspace and hence allow vdso gettimeofday to work. Signed-off-by:
Joao Martins <joao.m.martins@oracle.com> Signed-off-by:
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Joao Martins authored
Parameterise kvm_setup_pvclock_page() a little bit so that it can be invoked for different gfn_to_hva_cache structures, and with different offsets. Then we can invoke it for the normal KVM pvclock and also for the Xen one in the vcpu_info. Signed-off-by:
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Joao Martins authored
The vcpu info supersedes the per vcpu area of the shared info page and the guest vcpus will use this instead. Signed-off-by:
Ankur Arora <ankur.a.arora@oracle.com> Signed-off-by:
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David Woodhouse authored
This will be used for per-vCPU setup such as runstate and vcpu_info. Signed-off-by: -
Joao Martins authored
Wallclock on Xen is written in the shared_info page. To that purpose, export kvm_write_wall_clock() and pass on the GPA of its location to populate the shared_info wall clock data. Signed-off-by:
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David Woodhouse authored
Xen added this in 2015 (Xen 4.6). On x86_64 and Arm it fills what was previously a 32-bit hole in the generic shared_info structure; on i386 it had to go at the end of struct arch_shared_info. Signed-off-by: -
Joao Martins authored
Add KVM_XEN_ATTR_TYPE_SHARED_INFO to allow hypervisor to know where the guest's shared info page is. Signed-off-by:
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David Woodhouse authored
There aren't a lot of differences for the things that the kernel needs to care about, but there are a few. Signed-off-by: -
David Woodhouse authored
Signed-off-by: -
Joao Martins authored
This will be used to set up shared info pages etc. Signed-off-by:
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David Woodhouse authored
The code paths for Xen support are all fairly lightweight but if we hide them behind this, they're even *more* lightweight for any system which isn't actually hosting Xen guests. Signed-off-by: -
David Woodhouse authored
This is already more complex than the simple memcpy it originally had. Move it to xen.c with the rest of the Xen support. Signed-off-by: -
Joao Martins authored
Disambiguate Xen vs. Hyper-V calls by adding 'orl $0x80000000, %eax' at the start of the Hyper-V hypercall page when Xen hypercalls are also enabled. That bit is reserved in the Hyper-V ABI, and those hypercall numbers will never be used by Xen (because it does precisely the same trick). Switch to using kvm_vcpu_write_guest() while we're at it, instead of open-coding it. Signed-off-by: -
Joao Martins authored
Add a new exit reason for emulator to handle Xen hypercalls. Since this means KVM owns the ABI, dispense with the facility for the VMM to provide its own copy of the hypercall pages; just fill them in directly using VMCALL/VMMCALL as we do for the Hyper-V hypercall page. This behaviour is enabled by a new INTERCEPT_HCALL flag in the KVM_XEN_HVM_CONFIG ioctl structure, and advertised by the same flag being returned from the KVM_CAP_XEN_HVM check. Rename xen_hvm_config() to kvm_xen_write_hypercall_page() and move it to the nascent xen.c while we're at it, and add a test case. Signed-off-by:
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David Woodhouse authored
The address we give to memdup_user() isn't correctly tagged as __user. This is harmless enough as it's a one-off use and we're doing exactly the right thing, but fix it anyway to shut the checker up. Otherwise it'll whine when the (now legacy) code gets moved around in a later patch. Signed-off-by: -
Joao Martins authored
Xen usually places its MSR at 0x40000000 or 0x40000200 depending on whether it is running in viridian mode or not. Note that this is not ABI guaranteed, so it is possible for Xen to advertise the MSR some place else. Given the way xen_hvm_config() is handled, if the former address is selected, this will conflict with Hyper-V's MSR (HV_X64_MSR_GUEST_OS_ID) which unconditionally uses the same address. Given that the MSR location is arbitrary, move the xen_hvm_config() handling to the top of kvm_set_msr_common() before falling through. Signed-off-by:
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Ben Gardon authored
Make the last few changes necessary to enable the TDP MMU to handle page faults in parallel while holding the mmu_lock in read mode. Reviewed-by:
Peter Feiner <pfeiner@google.com> Signed-off-by:
Ben Gardon <bgardon@google.com> Message-Id: <20210202185734.1680553-24-bgardon@google.com> Signed-off-by:
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Ben Gardon authored
When clearing TDP MMU pages what have been disconnected from the paging structure root, set the SPTEs to a special non-present value which will not be overwritten by other threads. This is needed to prevent races in which a thread is clearing a disconnected page table, but another thread has already acquired a pointer to that memory and installs a mapping in an already cleared entry. This can lead to memory leaks and accounting errors. Reviewed-by:
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Ben Gardon authored
When the TDP MMU is allowed to handle page faults in parallel there is the possiblity of a race where an SPTE is cleared and then imediately replaced with a present SPTE pointing to a different PFN, before the TLBs can be flushed. This race would violate architectural specs. Ensure that the TLBs are flushed properly before other threads are allowed to install any present value for the SPTE. Reviewed-by:
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Ben Gardon authored
To prepare for handling page faults in parallel, change the TDP MMU page fault handler to use atomic operations to set SPTEs so that changes are not lost if multiple threads attempt to modify the same SPTE. Reviewed-by:
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Ben Gardon authored
Move the work of adding and removing TDP MMU pages to/from "secondary" data structures to helper functions. These functions will be built on in future commits to enable MMU operations to proceed (mostly) in parallel. No functional change expected. Signed-off-by:
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Ben Gardon authored
Add a read / write lock to be used in place of the MMU spinlock on x86. The rwlock will enable the TDP MMU to handle page faults, and other operations in parallel in future commits. Reviewed-by:
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Ben Gardon authored
Safely rescheduling while holding a spin lock is essential for keeping long running kernel operations running smoothly. Add the facility to cond_resched rwlocks. CC: Ingo Molnar <mingo@redhat.com> CC: Will Deacon <will@kernel.org> Acked-by:
Peter Zijlstra <peterz@infradead.org> Acked-by:
Davidlohr Bueso <dbueso@suse.de> Acked-by:
Waiman Long <longman@redhat.com> Acked-by:
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Ben Gardon authored
Contention awareness while holding a spin lock is essential for reducing latency when long running kernel operations can hold that lock. Add the same contention detection interface for read/write spin locks. CC: Ingo Molnar <mingo@redhat.com> CC: Will Deacon <will@kernel.org> Acked-by:
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Ben Gardon authored
rwlocks do not currently have any facility to detect contention like spinlocks do. In order to allow users of rwlocks to better manage latency, add contention detection for queued rwlocks. CC: Ingo Molnar <mingo@redhat.com> CC: Will Deacon <will@kernel.org> Acked-by:
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Ben Gardon authored
In order to enable concurrent modifications to the paging structures in the TDP MMU, threads must be able to safely remove pages of page table memory while other threads are traversing the same memory. To ensure threads do not access PT memory after it is freed, protect PT memory with RCU. Protecting concurrent accesses to page table memory from use-after-free bugs could also have been acomplished using walk_shadow_page_lockless_begin/end() and READING_SHADOW_PAGE_TABLES, coupling with the barriers in a TLB flush. The use of RCU for this case has several distinct advantages over that approach. 1. Disabling interrupts for long running operations is not desirable. Future commits will allow operations besides page faults to operate without the exclusive protection of the MMU lock and those operations are too long to disable iterrupts for their duration. 2. The use of RCU here avoids long blocking / spinning operations in perfromance critical paths. By freeing memory with an asynchronous RCU API we avoid the longer wait times TLB flushes experience when overlapping with a thread in walk_shadow_page_lockless_begin/end(). 3. RCU provides a separation of concerns when removing memory from the paging structure. Because the RCU callback to free memory can be scheduled immediately after a TLB flush, there's no need for the thread to manually free a queue of pages later, as commit_zap_pages does. Fixes: 95fb5b02 ("kvm: x86/mmu: Support MMIO in the TDP MMU") Reviewed-by:
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Ben Gardon authored
In clear_dirty_pt_masked, the loop is intended to exit early after processing each of the GFNs with corresponding bits set in mask. This does not work as intended if another thread has already cleared the dirty bit or writable bit on the SPTE. In that case, the loop would proceed to the next iteration early and the bit in mask would not be cleared. As a result the loop could not exit early and would proceed uselessly. Move the unsetting of the mask bit before the check for a no-op SPTE change. Fixes: a6a0b05d ("kvm: x86/mmu: Support dirty logging for the TDP MMU") Suggested-by:
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Ben Gardon authored
Skip setting SPTEs if no change is expected. Reviewed-by:
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