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    SubjectRe: [PATCH 2/3] x86/mm: Sync also unmappings in vmalloc_sync_one()
    On Wed, 17 Jul 2019, Joerg Roedel wrote:

    > From: Joerg Roedel <jroedel@suse.de>
    >
    > With huge-page ioremap areas the unmappings also need to be
    > synced between all page-tables. Otherwise it can cause data
    > corruption when a region is unmapped and later re-used.
    >
    > Make the vmalloc_sync_one() function ready to sync
    > unmappings.
    >
    > Fixes: 5d72b4fba40ef ('x86, mm: support huge I/O mapping capability I/F')
    > Signed-off-by: Joerg Roedel <jroedel@suse.de>
    > ---
    > arch/x86/mm/fault.c | 7 ++++---
    > 1 file changed, 4 insertions(+), 3 deletions(-)
    >
    > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
    > index 4a4049f6d458..d71e167662c3 100644
    > --- a/arch/x86/mm/fault.c
    > +++ b/arch/x86/mm/fault.c
    > @@ -194,11 +194,12 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
    >
    > pmd = pmd_offset(pud, address);
    > pmd_k = pmd_offset(pud_k, address);
    > - if (!pmd_present(*pmd_k))
    > - return NULL;
    >
    > - if (!pmd_present(*pmd))
    > + if (pmd_present(*pmd) ^ pmd_present(*pmd_k))
    > set_pmd(pmd, *pmd_k);
    > +
    > + if (!pmd_present(*pmd_k))
    > + return NULL;
    > else
    > BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));

    So in case of unmap, this updates only the first entry in the pgd_list
    because vmalloc_sync_all() will break out of the iteration over pgd_list
    when NULL is returned from vmalloc_sync_one().

    I'm surely missing something, but how is that supposed to sync _all_ page
    tables on unmap as the changelog claims?

    Thanks,

    tglx

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