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| author | Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> | 2020-05-05 12:47:13 +0530 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-05-05 21:20:14 +1000 |
| commit | 0da81b658b5bf5c16abe51eb32f1905a32322f53 (patch) | |
| tree | 3ee126bd3f0a01d50de0918909278a74f902f5c6 | |
| parent | 2f92447f9f96583112420aa3cfb400ded55f667e (diff) | |
| download | linux-0da81b658b5bf5c16abe51eb32f1905a32322f53.tar.gz linux-0da81b658b5bf5c16abe51eb32f1905a32322f53.tar.bz2 linux-0da81b658b5bf5c16abe51eb32f1905a32322f53.zip | |
powerpc/mce: Don't reload pte val in addr_to_pfn
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: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200505071729.54912-7-aneesh.kumar@linux.ibm.com
| -rw-r--r-- | arch/powerpc/kernel/mce_power.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c index 067b094bfeff..1d18991f3854 100644 --- a/arch/powerpc/kernel/mce_power.c +++ b/arch/powerpc/kernel/mce_power.c @@ -27,7 +27,7 @@ */ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr) { - pte_t *ptep; + pte_t *ptep, pte; unsigned int shift; unsigned long pfn, flags; struct mm_struct *mm; @@ -39,19 +39,23 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr) local_irq_save(flags); ptep = __find_linux_pte(mm->pgd, addr, NULL, &shift); + if (!ptep) { + pfn = ULONG_MAX; + goto out; + } + pte = READ_ONCE(*ptep); - if (!ptep || pte_special(*ptep)) { + if (!pte_present(pte) || pte_special(pte)) { pfn = ULONG_MAX; goto out; } if (shift <= PAGE_SHIFT) - pfn = pte_pfn(*ptep); + pfn = pte_pfn(pte); else { unsigned long rpnmask = (1ul << shift) - PAGE_SIZE; - pfn = pte_pfn(__pte(pte_val(*ptep) | (addr & rpnmask))); + pfn = pte_pfn(__pte(pte_val(pte) | (addr & rpnmask))); } - out: local_irq_restore(flags); return pfn; |