Re: Re: [PATCH v2 1/1] mm/memory-failure: don't allow to unpoison hw corrupted page

[zhenwei pi]

On 6/8/22 17:30, David Hildenbrand wrote:
> 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@xxxxxxx>
> > Signed-off-by: zhenwei pi <pizhenwei@xxxxxxxxxxxxx>
> > ---
> >   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.

Hi,

I dived into this part and noticed that both pmd_off_k() and 
virt_to_kpte() are broken.

For example, on a x86 platform, if the CPU has feature 'pdpe1gb', the 
kernel prefers 1G map. (cat /proc/meminfo | grep DirectMap to show the 
current mapping)

static inline pmd_t *pmd_off_k(unsigned long va)
{
        return pmd_offset(pud_offset(p4d_offset(pgd_offset_k(va), va), 
va), va);
}

There is no pud_none() & pud_large()(of cause, we can't use pud_large() 
here) to test *PUD* valid or not.

So I'm going to do:
- in pmd_off_k(), use pud_none() and pud_bad() to test *PUD*, if failed, 
BUG().
- in virt_to_kpte(), use pmd_none() & pmd_bad() to test *PMD*, if 
failed, BUG().
- rework KPTE test in unpoison_memory(), walk page table instead of 
useing virt_to_kpte().

Do you have any suggestions?

--
zhenwei pi