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

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Message-ID: <4b87dee3-fbdf-6057-f2b3-71376a13a742@amd.com>
Date:   Fri, 28 Apr 2023 10:50:39 +0530
From:   Vasant Hegde <vasant.hegde@....com>
To:     Jon Pan-Doh <pandoh@...gle.com>, Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Nadav Amit <namit@...are.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Sudheer Dantuluri <dantuluris@...gle.com>,
        Gary Zibrat <gzibrat@...gle.com>
Subject: Re: [PATCH] iommu/amd: Fix domain flush size when syncing iotlb

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@...gle.com>
> Tested-by: Sudheer Dantuluri <dantuluris@...gle.com>
> Suggested-by: Gary Zibrat <gzibrat@...gle.com>

Thanks!

Reviewed-by: Vasant Hegde <vasant.hegde@....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);
>  }