On Wed, 17 Jul 2019, Joerg Roedel wrote:

> From: Joerg Roedel <jroe...@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 <jroe...@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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