Commit 691e95fd authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Michael Ellerman

powerpc/mm/thp: Make page table walk safe against thp split/collapse

We can disable a THP split or a hugepage collapse by disabling irq.
We do send IPI to all the cpus in the early part of split/collapse,
and disabling local irq ensure we don't make progress with
split/collapse. If the THP is getting split we return NULL from
find_linux_pte_or_hugepte(). For all the current callers it should be ok.
We need to be careful if we want to use returned pte_t pointer outside
the irq disabled region. W.r.t to THP split, the pfn remains the same,
but then a hugepage collapse will result in a pfn change. There are
few steps we can take to avoid a hugepage collapse.One way is to take page
reference inside the irq disable region. Other option is to take
mmap_sem so that a parallel collapse will not happen. We can also
disable collapse by taking pmd_lock. Another method used by kvm
subsystem is to check whether we had a mmu_notifer update in between
using mmu_notifier_retry().
Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent dac56570
......@@ -247,8 +247,17 @@ extern int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
#define pmd_large(pmd) 0
#define has_transparent_hugepage() 0
#endif
pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
unsigned *shift);
static inline pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
unsigned *shift)
{
if (!arch_irqs_disabled()) {
pr_info("%s called with irq enabled\n", __func__);
dump_stack();
}
return __find_linux_pte_or_hugepte(pgdir, ea, shift);
}
#endif /* __ASSEMBLY__ */
#endif /* __KERNEL__ */
......
......@@ -334,9 +334,11 @@ static inline unsigned long eeh_token_to_phys(unsigned long token)
int hugepage_shift;
/*
* We won't find hugepages here, iomem
* We won't find hugepages here(this is iomem). Hence we are not
* worried about _PAGE_SPLITTING/collapse. Also we will not hit
* page table free, because of init_mm.
*/
ptep = find_linux_pte_or_hugepte(init_mm.pgd, token, &hugepage_shift);
ptep = __find_linux_pte_or_hugepte(init_mm.pgd, token, &hugepage_shift);
if (!ptep)
return token;
WARN_ON(hugepage_shift);
......
......@@ -71,15 +71,15 @@ struct iowa_bus *iowa_mem_find_bus(const PCI_IO_ADDR addr)
vaddr = (unsigned long)PCI_FIX_ADDR(addr);
if (vaddr < PHB_IO_BASE || vaddr >= PHB_IO_END)
return NULL;
ptep = find_linux_pte_or_hugepte(init_mm.pgd, vaddr,
/*
* We won't find huge pages here (iomem). Also can't hit
* a page table free due to init_mm
*/
ptep = __find_linux_pte_or_hugepte(init_mm.pgd, vaddr,
&hugepage_shift);
if (ptep == NULL)
paddr = 0;
else {
/*
* we don't have hugepages backing iomem
*/
WARN_ON(hugepage_shift);
paddr = pte_pfn(*ptep) << PAGE_SHIFT;
}
......
......@@ -539,12 +539,13 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
if (!writing && hpte_is_writable(r)) {
unsigned int hugepage_shift;
pte_t *ptep, pte;
unsigned long flags;
/*
* We need to protect against page table destruction
* while looking up and updating the pte.
*/
rcu_read_lock_sched();
local_irq_save(flags);
ptep = find_linux_pte_or_hugepte(current->mm->pgd,
hva, &hugepage_shift);
if (ptep) {
......@@ -553,7 +554,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
if (pte_write(pte))
write_ok = 1;
}
rcu_read_unlock_sched();
local_irq_restore(flags);
}
}
......
......@@ -26,11 +26,14 @@ static void *real_vmalloc_addr(void *x)
{
unsigned long addr = (unsigned long) x;
pte_t *p;
p = find_linux_pte_or_hugepte(swapper_pg_dir, addr, NULL);
/*
* assume we don't have huge pages in vmalloc space...
* So don't worry about THP collapse/split. Called
* Only in realmode, hence won't need irq_save/restore.
*/
p = __find_linux_pte_or_hugepte(swapper_pg_dir, addr, NULL);
if (!p || !pte_present(*p))
return NULL;
/* assume we don't have huge pages in vmalloc space... */
addr = (pte_pfn(*p) << PAGE_SHIFT) | (addr & ~PAGE_MASK);
return __va(addr);
}
......@@ -153,7 +156,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
pte_t *ptep;
unsigned int writing;
unsigned long mmu_seq;
unsigned long rcbits;
unsigned long rcbits, irq_flags = 0;
psize = hpte_page_size(pteh, ptel);
if (!psize)
......@@ -189,7 +192,16 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
/* Translate to host virtual address */
hva = __gfn_to_hva_memslot(memslot, gfn);
ptep = find_linux_pte_or_hugepte(pgdir, hva, &hpage_shift);
/*
* If we had a page table table change after lookup, we would
* retry via mmu_notifier_retry.
*/
if (realmode)
ptep = __find_linux_pte_or_hugepte(pgdir, hva, &hpage_shift);
else {
local_irq_save(irq_flags);
ptep = find_linux_pte_or_hugepte(pgdir, hva, &hpage_shift);
}
if (ptep) {
pte_t pte;
unsigned int host_pte_size;
......@@ -202,9 +214,11 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
* We should always find the guest page size
* to <= host page size, if host is using hugepage
*/
if (host_pte_size < psize)
if (host_pte_size < psize) {
if (!realmode)
local_irq_restore(flags);
return H_PARAMETER;
}
pte = kvmppc_read_update_linux_pte(ptep, writing, hpage_shift);
if (pte_present(pte) && !pte_protnone(pte)) {
if (writing && !pte_write(pte))
......@@ -216,6 +230,8 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
pa |= gpa & ~PAGE_MASK;
}
}
if (!realmode)
local_irq_restore(irq_flags);
ptel &= ~(HPTE_R_PP0 - psize);
ptel |= pa;
......
......@@ -338,6 +338,7 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
pte_t *ptep;
unsigned int wimg = 0;
pgd_t *pgdir;
unsigned long flags;
/* used to check for invalidations in progress */
mmu_seq = kvm->mmu_notifier_seq;
......@@ -468,14 +469,23 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
pgdir = vcpu_e500->vcpu.arch.pgdir;
/*
* We are just looking at the wimg bits, so we don't
* care much about the trans splitting bit.
* We are holding kvm->mmu_lock so a notifier invalidate
* can't run hence pfn won't change.
*/
local_irq_save(flags);
ptep = find_linux_pte_or_hugepte(pgdir, hva, NULL);
if (ptep) {
pte_t pte = READ_ONCE(*ptep);
if (pte_present(pte))
if (pte_present(pte)) {
wimg = (pte_val(pte) >> PTE_WIMGE_SHIFT) &
MAS2_WIMGE_MASK;
else {
local_irq_restore(flags);
} else {
local_irq_restore(flags);
pr_err_ratelimited("%s: pte not present: gfn %lx,pfn %lx\n",
__func__, (long)gfn, pfn);
ret = -EINVAL;
......
......@@ -1066,7 +1066,7 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea,
#endif /* CONFIG_PPC_64K_PAGES */
/* Get PTE and page size from page tables */
ptep = find_linux_pte_or_hugepte(pgdir, ea, &hugeshift);
ptep = __find_linux_pte_or_hugepte(pgdir, ea, &hugeshift);
if (ptep == NULL || !pte_present(*ptep)) {
DBG_LOW(" no PTE !\n");
rc = 1;
......
......@@ -109,7 +109,7 @@ int pgd_huge(pgd_t pgd)
pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
{
/* Only called for hugetlbfs pages, hence can ignore THP */
return find_linux_pte_or_hugepte(mm->pgd, addr, NULL);
return __find_linux_pte_or_hugepte(mm->pgd, addr, NULL);
}
static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
......@@ -682,28 +682,35 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb,
} while (addr = next, addr != end);
}
/*
* We are holding mmap_sem, so a parallel huge page collapse cannot run.
* To prevent hugepage split, disable irq.
*/
struct page *
follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
{
pte_t *ptep;
struct page *page;
unsigned shift;
unsigned long mask;
unsigned long mask, flags;
/*
* Transparent hugepages are handled by generic code. We can skip them
* here.
*/
local_irq_save(flags);
ptep = find_linux_pte_or_hugepte(mm->pgd, address, &shift);
/* Verify it is a huge page else bail. */
if (!ptep || !shift || pmd_trans_huge(*(pmd_t *)ptep))
if (!ptep || !shift || pmd_trans_huge(*(pmd_t *)ptep)) {
local_irq_restore(flags);
return ERR_PTR(-EINVAL);
}
mask = (1UL << shift) - 1;
page = pte_page(*ptep);
if (page)
page += (address & mask) / PAGE_SIZE;
local_irq_restore(flags);
return page;
}
......@@ -950,9 +957,12 @@ void flush_dcache_icache_hugepage(struct page *page)
*
* So long as we atomically load page table pointers we are safe against teardown,
* we can follow the address down to the the page and take a ref on it.
* This function need to be called with interrupts disabled. We use this variant
* when we have MSR[EE] = 0 but the paca->soft_enabled = 1
*/
pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift)
pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
unsigned *shift)
{
pgd_t pgd, *pgdp;
pud_t pud, *pudp;
......@@ -1031,7 +1041,7 @@ pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift
*shift = pdshift;
return ret_pte;
}
EXPORT_SYMBOL_GPL(find_linux_pte_or_hugepte);
EXPORT_SYMBOL_GPL(__find_linux_pte_or_hugepte);
int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
......
......@@ -111,41 +111,45 @@ perf_callchain_kernel(struct perf_callchain_entry *entry, struct pt_regs *regs)
* interrupt context, so if the access faults, we read the page tables
* to find which page (if any) is mapped and access it directly.
*/
static int read_user_stack_slow(void __user *ptr, void *ret, int nb)
static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
{
int ret = -EFAULT;
pgd_t *pgdir;
pte_t *ptep, pte;
unsigned shift;
unsigned long addr = (unsigned long) ptr;
unsigned long offset;
unsigned long pfn;
unsigned long pfn, flags;
void *kaddr;
pgdir = current->mm->pgd;
if (!pgdir)
return -EFAULT;
local_irq_save(flags);
ptep = find_linux_pte_or_hugepte(pgdir, addr, &shift);
if (!ptep)
goto err_out;
if (!shift)
shift = PAGE_SHIFT;
/* align address to page boundary */
offset = addr & ((1UL << shift) - 1);
addr -= offset;
if (ptep == NULL)
return -EFAULT;
pte = *ptep;
pte = READ_ONCE(*ptep);
if (!pte_present(pte) || !(pte_val(pte) & _PAGE_USER))
return -EFAULT;
goto err_out;
pfn = pte_pfn(pte);
if (!page_is_ram(pfn))
return -EFAULT;
goto err_out;
/* no highmem to worry about here */
kaddr = pfn_to_kaddr(pfn);
memcpy(ret, kaddr + offset, nb);
return 0;
memcpy(buf, kaddr + offset, nb);
ret = 0;
err_out:
local_irq_restore(flags);
return ret;
}
static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
......
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