linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Disallow dirty tracking if incoherent page walk

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Message-ID: <485b2ba8-273d-494b-a778-c5dd7fd0631b@linux.intel.com>
Date: Fri, 26 Sep 2025 10:42:16 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Kevin Tian <kevin.tian@...el.com>,
 Jason Gunthorpe <jgg@...dia.com>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Disallow dirty tracking if incoherent
 page walk

On 9/24/25 16:34, Lu Baolu wrote:
> Dirty page tracking relies on the IOMMU atomically updating the dirty bit
> in the paging-structure entry. For this operation to succeed, the paging-
> structure memory must be coherent between the IOMMU and the CPU. In
> another word, if the iommu page walk is incoherent, dirty page tracking
> doesn't work.
> 
> The Intel VT-d specification, Section 3.10 "Snoop Behavior" states:
> 
> "Remapping hardware encountering the need to atomically update A/EA/D bits
>   in a paging-structure entry that is not snooped will result in a non-
>   recoverable fault."
> 
> To prevent an IOMMU from being incorrectly configured for dirty page
> tracking when it is operating in an incoherent mode, mark SSADS as
> supported only when both ecap_slads and ecap_smpwc are supported.
> 
> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
> ---
>   drivers/iommu/intel/iommu.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

Queued for v6.18-rc1.