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    Subject[PATCH 5.6 100/167] mm/hugetlb: fix a addressing exception caused by huge_pte_offset
    Date
    From: Longpeng <longpeng2@huawei.com>

    commit 3c1d7e6ccb644d517a12f73a7ff200870926f865 upstream.

    Our machine encountered a panic(addressing exception) after run for a
    long time and the calltrace is:

    RIP: 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:
    follow_hugetlb_page+0x175/0x540
    __get_user_pages+0x2a0/0x7e0
    __get_user_pages_unlocked+0x15d/0x210
    __gfn_to_pfn_memslot+0x3c5/0x460 [kvm]
    try_async_pf+0x6e/0x2a0 [kvm]
    tdp_page_fault+0x151/0x2d0 [kvm]
    ...
    kvm_arch_vcpu_ioctl_run+0x330/0x490 [kvm]
    kvm_vcpu_ioctl+0x309/0x6d0 [kvm]
    do_vfs_ioctl+0x3f0/0x540
    SyS_ioctl+0xa1/0xc0
    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:

    - CPU0: sz = PUD_SIZE and *pud = 0 , continue
    - CPU0: "pud_huge(*pud)" is false
    - CPU1: calling hugetlb_no_page and set *pud to xxxx8e7(PRESENT)
    - CPU0: "!pud_present(*pud)" is false, continue
    - 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.

    Signed-off-by: Longpeng <longpeng2@huawei.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
    Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Sean Christopherson <sean.j.christopherson@intel.com>
    Cc: <stable@vger.kernel.org>
    Link: http://lkml.kernel.org/r/20200413010342.771-1-longpeng2@huawei.com
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/hugetlb.c | 14 ++++++++------
    1 file changed, 8 insertions(+), 6 deletions(-)

    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -4910,8 +4910,8 @@ pte_t *huge_pte_offset(struct mm_struct
    {
    pgd_t *pgd;
    p4d_t *p4d;
    - pud_t *pud;
    - pmd_t *pmd;
    + pud_t *pud, pud_entry;
    + pmd_t *pmd, pmd_entry;

    pgd = pgd_offset(mm, addr);
    if (!pgd_present(*pgd))
    @@ -4921,17 +4921,19 @@ pte_t *huge_pte_offset(struct mm_struct
    return NULL;

    pud = pud_offset(p4d, addr);
    - if (sz != PUD_SIZE && pud_none(*pud))
    + pud_entry = READ_ONCE(*pud);
    + if (sz != PUD_SIZE && pud_none(pud_entry))
    return NULL;
    /* hugepage or swap? */
    - if (pud_huge(*pud) || !pud_present(*pud))
    + if (pud_huge(pud_entry) || !pud_present(pud_entry))
    return (pte_t *)pud;

    pmd = pmd_offset(pud, addr);
    - if (sz != PMD_SIZE && pmd_none(*pmd))
    + pmd_entry = READ_ONCE(*pmd);
    + if (sz != PMD_SIZE && pmd_none(pmd_entry))
    return NULL;
    /* hugepage or swap? */
    - if (pmd_huge(*pmd) || !pmd_present(*pmd))
    + if (pmd_huge(pmd_entry) || !pmd_present(pmd_entry))
    return (pte_t *)pmd;

    return NULL;

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