Re: [Xen-devel] [PATCH for-4.12] amd/iommu: fix present bit checking when clearing PTE

["Woods, Brian" <Brian.Woods@xxxxxxx>]

On 1/23/19 3:47 AM, Roger Pau Monne wrote:
> The current check for the present bit is wrong, since the present bit
> is located in the low part of the entry.
> 
> Fixes: e8afe1124cc1 ("iommu: elide flushing for higher order map/unmap 
> operations")
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Brian Woods <brian.woods@xxxxxxx>

> ---
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> Cc: Brian Woods <brian.woods@xxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
>   xen/drivers/passthrough/amd/iommu_map.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/xen/drivers/passthrough/amd/iommu_map.c 
> b/xen/drivers/passthrough/amd/iommu_map.c
> index 99ac0a6862..67329b0c95 100644
> --- a/xen/drivers/passthrough/amd/iommu_map.c
> +++ b/xen/drivers/passthrough/amd/iommu_map.c
> @@ -39,15 +39,13 @@ static unsigned int clear_iommu_pte_present(unsigned long 
> l1_mfn,
>                                               unsigned long dfn)
>   {
>       uint64_t *table, *pte;
> -    uint32_t entry;
>       unsigned int flush_flags;
>   
>       table = map_domain_page(_mfn(l1_mfn));
>   
>       pte = (table + pfn_to_pde_idx(dfn, 1));
> -    entry = *pte >> 32;
>   
> -    flush_flags = get_field_from_reg_u32(entry, IOMMU_PTE_PRESENT_MASK,
> +    flush_flags = get_field_from_reg_u32(*pte, IOMMU_PTE_PRESENT_MASK,
>                                            IOMMU_PTE_PRESENT_SHIFT) ?
>                                            IOMMU_FLUSHF_modified : 0;
>   
> 

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