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    SubjectRe: [PATCH v2 1/1] mm/memory-failure: don't allow to unpoison hw corrupted page
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    On 08.06.22 10:43, zhenwei pi wrote:
    > Currently unpoison_memory(unsigned long pfn) is designed for soft
    > poison(hwpoison-inject) only. Since 17fae1294ad9d, the KPTE gets
    > cleared on a x86 platform once hardware memory corrupts.
    >
    > Unpoisoning a hardware corrupted page puts page back buddy only,
    > the kernel has a chance to access the page with *NOT PRESENT* KPTE.
    > This leads BUG during accessing on the corrupted KPTE.
    >
    > Do not allow to unpoison hardware corrupted page in unpoison_memory() to
    > avoid BUG like this:
    >
    > Unpoison: Software-unpoisoned page 0x61234
    > BUG: unable to handle page fault for address: ffff888061234000
    > #PF: supervisor write access in kernel mode
    > #PF: error_code(0x0002) - not-present page
    > PGD 2c01067 P4D 2c01067 PUD 107267063 PMD 10382b063 PTE 800fffff9edcb062
    > Oops: 0002 [#1] PREEMPT SMP NOPTI
    > CPU: 4 PID: 26551 Comm: stress Kdump: loaded Tainted: G M OE 5.18.0.bm.1-amd64 #7
    > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ...
    > RIP: 0010:clear_page_erms+0x7/0x10
    > Code: ...
    > RSP: 0000:ffffc90001107bc8 EFLAGS: 00010246
    > RAX: 0000000000000000 RBX: 0000000000000901 RCX: 0000000000001000
    > RDX: ffffea0001848d00 RSI: ffffea0001848d40 RDI: ffff888061234000
    > RBP: ffffea0001848d00 R08: 0000000000000901 R09: 0000000000001276
    > R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000001
    > R13: 0000000000000000 R14: 0000000000140dca R15: 0000000000000001
    > FS: 00007fd8b2333740(0000) GS:ffff88813fd00000(0000) knlGS:0000000000000000
    > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > CR2: ffff888061234000 CR3: 00000001023d2005 CR4: 0000000000770ee0
    > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    > PKRU: 55555554
    > Call Trace:
    > <TASK>
    > prep_new_page+0x151/0x170
    > get_page_from_freelist+0xca0/0xe20
    > ? sysvec_apic_timer_interrupt+0xab/0xc0
    > ? asm_sysvec_apic_timer_interrupt+0x1b/0x20
    > __alloc_pages+0x17e/0x340
    > __folio_alloc+0x17/0x40
    > vma_alloc_folio+0x84/0x280
    > __handle_mm_fault+0x8d4/0xeb0
    > handle_mm_fault+0xd5/0x2a0
    > do_user_addr_fault+0x1d0/0x680
    > ? kvm_read_and_reset_apf_flags+0x3b/0x50
    > exc_page_fault+0x78/0x170
    > asm_exc_page_fault+0x27/0x30
    >
    > Fixes: 847ce401df392 ("HWPOISON: Add unpoisoning support")
    > Fixes: 17fae1294ad9d ("x86/{mce,mm}: Unmap the entire page if the whole page is affected and poisoned")
    > Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
    > Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
    > ---
    > mm/memory-failure.c | 9 +++++++++
    > 1 file changed, 9 insertions(+)
    >
    > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
    > index b85661cbdc4a..da99a2b7ef35 100644
    > --- a/mm/memory-failure.c
    > +++ b/mm/memory-failure.c
    > @@ -2090,6 +2090,7 @@ int unpoison_memory(unsigned long pfn)
    > {
    > struct page *page;
    > struct page *p;
    > + pte_t *kpte;
    > int ret = -EBUSY;
    > int freeit = 0;
    > static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
    > @@ -2103,6 +2104,14 @@ int unpoison_memory(unsigned long pfn)
    >
    > mutex_lock(&mf_mutex);
    >
    > + kpte = virt_to_kpte((unsigned long)page_to_virt(p));
    >
    I'm curious whether virt_to_kpte is sane to use, especially, when having
    the direct map map PMDs and not PTEs?

    virt_to_kpte() only checks for pmd_none() -- but what if we have
    pmd_large()?

    Naive me would assume that calling virt_to_kpte() from generic code is
    broken. Only mm/highmem.c uses it, however, 32bit most probably also
    doesn't have large mappings in the page tables for the direct map.

    --
    Thanks,

    David / dhildenb

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