Re: [PATCH v5] mm/hugetlb: fix a addressing exception caused by huge_pte_offset

[Jason Gunthorpe]

On Mon, Apr 13, 2020 at 09:03:42AM +0800, Longpeng(Mike) wrote:
> From: Longpeng <longpeng2@xxxxxxxxxx>
> 
> Our machine encountered a panic(addressing exception) after run
> for a long time and the calltrace is:
> RIP: 0010:[<ffffffff9dff0587>]  [<ffffffff9dff0587>] hugetlb_fault+0x307/0xbe0
> RSP: 0018:ffff9567fc27f808  EFLAGS: 00010286
> RAX: e800c03ff1258d48 RBX: ffffd3bb003b69c0 RCX: e800c03ff1258d48
> RDX: 17ff3fc00eda72b7 RSI: 00003ffffffff000 RDI: e800c03ff1258d48
> RBP: ffff9567fc27f8c8 R08: e800c03ff1258d48 R09: 0000000000000080
> R10: ffffaba0704c22a8 R11: 0000000000000001 R12: ffff95c87b4b60d8
> R13: 00005fff00000000 R14: 0000000000000000 R15: ffff9567face8074
> FS:  00007fe2d9ffb700(0000) GS:ffff956900e40000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffd3bb003b69c0 CR3: 000000be67374000 CR4: 00000000003627e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  [<ffffffff9df9b71b>] ? unlock_page+0x2b/0x30
>  [<ffffffff9dff04a2>] ? hugetlb_fault+0x222/0xbe0
>  [<ffffffff9dff1405>] follow_hugetlb_page+0x175/0x540
>  [<ffffffff9e15b825>] ? cpumask_next_and+0x35/0x50
>  [<ffffffff9dfc7230>] __get_user_pages+0x2a0/0x7e0
>  [<ffffffff9dfc648d>] __get_user_pages_unlocked+0x15d/0x210
>  [<ffffffffc068cfc5>] __gfn_to_pfn_memslot+0x3c5/0x460 [kvm]
>  [<ffffffffc06b28be>] try_async_pf+0x6e/0x2a0 [kvm]
>  [<ffffffffc06b4b41>] tdp_page_fault+0x151/0x2d0 [kvm]
>  ...
>  [<ffffffffc06a6f90>] kvm_arch_vcpu_ioctl_run+0x330/0x490 [kvm]
>  [<ffffffffc068d919>] kvm_vcpu_ioctl+0x309/0x6d0 [kvm]
>  [<ffffffff9deaa8c2>] ? dequeue_signal+0x32/0x180
>  [<ffffffff9deae34d>] ? do_sigtimedwait+0xcd/0x230
>  [<ffffffff9e03aed0>] do_vfs_ioctl+0x3f0/0x540
>  [<ffffffff9e03b0c1>] SyS_ioctl+0xa1/0xc0
>  [<ffffffff9e53879b>] system_call_fastpath+0x22/0x27
> 
> For 1G hugepages, huge_pte_offset() wants to return NULL or pudp, but it
> may return a wrong 'pmdp' if there is a race. Please look at the following
> code snippet:
>     ...
>     pud = pud_offset(p4d, addr);
>     if (sz != PUD_SIZE && pud_none(*pud))
>         return NULL;
>     /* hugepage or swap? */
>     if (pud_huge(*pud) || !pud_present(*pud))
>         return (pte_t *)pud;
> 
>     pmd = pmd_offset(pud, addr);
>     if (sz != PMD_SIZE && pmd_none(*pmd))
>         return NULL;
>     /* hugepage or swap? */
>     if (pmd_huge(*pmd) || !pmd_present(*pmd))
>         return (pte_t *)pmd;
>     ...
> 
> The following sequence would trigger this bug:
> 1. CPU0: sz = PUD_SIZE and *pud = 0 , continue
> 1. CPU0: "pud_huge(*pud)" is false
> 2. CPU1: calling hugetlb_no_page and set *pud to xxxx8e7(PRESENT)
> 3. CPU0: "!pud_present(*pud)" is false, continue
> 4. CPU0: pmd = pmd_offset(pud, addr) and maybe return a wrong pmdp
> However, we want CPU0 to return NULL or pudp in this case.
> 
> We must make sure there is exactly one dereference of pud and pmd.
> 
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Longpeng <longpeng2@xxxxxxxxxx>
> ---
> v4 -> v5:
>   fix a bug of on i386
> v3 -> v4:
>   fix a typo s/p4g/p4d.  [Jason]
> v2 -> v3:
>   make sure p4d/pud/pmd be dereferenced once. [Jason]
> 
> ---
>  mm/hugetlb.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>

Jason