linux-kernel - Re: [PATCH] iommu/vt-d: Flush cache for PASID table before using it

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Message-ID: <f6fce114-ef7f-4541-8cc0-01c906c71a7c@linux.intel.com>
Date: Sun, 21 Dec 2025 16:11:01 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Dmytro Maluka <dmaluka@...omium.org>,
 David Woodhouse <dwmw2@...radead.org>, iommu@...ts.linux.dev
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org,
 "Vineeth Pillai (Google)" <vineeth@...byteword.org>,
 Aashish Sharma <aashish@...hishsharma.net>,
 Grzegorz Jaszczyk <jaszczyk@...omium.org>,
 Chuanxiao Dong <chuanxiao.dong@...el.com>, Kevin Tian <kevin.tian@...el.com>
Subject: Re: [PATCH] iommu/vt-d: Flush cache for PASID table before using it

On 12/21/25 08:17, Dmytro Maluka wrote:
> When writing the address of a freshly allocated zero-initialized PASID
> table to a PASID directory entry, do that after the CPU cache flush for
> this PASID table, not before it, to avoid the time window when this
> PASID table may be already used by non-coherent IOMMU hardware while
> its contents in RAM is still some random old data, not zero-initialized.
> 

Fixes: 194b3348bdbb ("iommu/vt-d: Fix PASID directory pointer coherency")

> Signed-off-by: Dmytro Maluka <dmaluka@...omium.org>
> ---
>   drivers/iommu/intel/pasid.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index 3e2255057079..77b9b147ab50 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -153,6 +153,9 @@ static struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid)
>   		if (!entries)
>   			return NULL;
>   
> +		if (!ecap_coherent(info->iommu->ecap))
> +			clflush_cache_range(entries, VTD_PAGE_SIZE);
> +
>   		/*
>   		 * The pasid directory table entry won't be freed after
>   		 * allocation. No worry about the race with free and
> @@ -165,10 +168,8 @@ static struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid)
>   			iommu_free_pages(entries);
>   			goto retry;
>   		}
> -		if (!ecap_coherent(info->iommu->ecap)) {
> -			clflush_cache_range(entries, VTD_PAGE_SIZE);
> +		if (!ecap_coherent(info->iommu->ecap))
>   			clflush_cache_range(&dir[dir_index].val, sizeof(*dir));
> -		}
>   	}
>   
>   	return &entries[index];

Thanks,
baolu