Re: [PATCH] iommu/amd: Fix domain flush size when syncing iotlb

[Vasant Hegde <vasant.hegde@amd.com>]

On 4/27/2023 2:02 AM, Jon Pan-Doh wrote:
> When running on an AMD vIOMMU, we observed multiple invalidations (of
> decreasing power of 2 aligned sizes) when unmapping a single page.
> 
> Domain flush takes gather bounds (end-start) as size param. However,
> gather->end is defined as the last inclusive address (start + size - 1).
> This leads to an off by 1 error.
> 
> With this patch, verified that 1 invalidation occurs when unmapping a
> single page.
> 
> Fixes: a270be1b3fdf ("iommu/amd: Use only natural aligned flushes in a VM")
> Signed-off-by: Jon Pan-Doh <pandoh@google.com>
> Tested-by: Sudheer Dantuluri <dantuluris@google.com>
> Suggested-by: Gary Zibrat <gzibrat@google.com>

Thanks!

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>

-Vasant


> ---
>  drivers/iommu/amd/iommu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 5a505ba5467e..da45b1ab042d 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2378,7 +2378,7 @@ static void amd_iommu_iotlb_sync(struct iommu_domain *domain,
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&dom->lock, flags);
> -	domain_flush_pages(dom, gather->start, gather->end - gather->start, 1);
> +	domain_flush_pages(dom, gather->start, gather->end - gather->start + 1, 1);
>  	amd_iommu_domain_flush_complete(dom);
>  	spin_unlock_irqrestore(&dom->lock, flags);
>  }