linux-kernel - Re: [PATCH rc v2 1/4] iommu/arm-smmu-v3: Add ignored bits to fix STE update sequence

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Message-ID: <60060fca-b1e7-43d9-b1de-27bc9ec2f43f@linux.alibaba.com>
Date: Mon, 8 Dec 2025 10:33:01 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
To: Nicolin Chen <nicolinc@...dia.com>, jgg@...dia.com, will@...nel.org,
 robin.murphy@....com
Cc: joro@...tes.org, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 skolothumtho@...dia.com, praan@...gle.com
Subject: Re: [PATCH rc v2 1/4] iommu/arm-smmu-v3: Add ignored bits to fix STE
 update sequence



在 2025/12/8 04:49, Nicolin Chen 写道:
> From: Jason Gunthorpe <jgg@...dia.com>
> 
> C_BAD_STE was observed when updating nested STE from an S1-bypass mode to
> an S1DSS-bypass mode. As both modes enabled S2, the used bit is slightly
> different than the normal S1-bypass and S1DSS-bypass modes. As a result,
> fields like MEV and EATS in S2's used list marked the word1 as a critical
> word that requested a STE.V=0. This breaks a hitless update.
> 
> However, both MEV and EATS aren't critical in terms of STE update. One
> controls the merge of the events and the other controls the ATS that is
> managed by the driver at the same time via pci_enable_ats().
> 
> Add an arm_smmu_get_ste_ignored() to allow STE update algorithm to ignore
> those fields, avoiding the STE update breakages.
> 
> Note that this change is required by both MEV and EATS fields, which were
> introduced in different kernel versions. So add this get_ignored() first.
> The MEV and EATS will be added in arm_smmu_get_ste_ignored() separately.
> 
> Fixes: 1e8be08d1c91 ("iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---

Reviewed-by: Shuai Xue <xueshuai@...ux.alibaba.com>

Thanks.
Shuai