linux-kernel - Re: [PATCH v5 4/4] iommu/amd: Skip enabling command/event buffers for kdump

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Message-ID: <7deb2d90-8a42-480b-b4e2-f784927160f8@amd.com>
Date: Thu, 21 Aug 2025 17:02:17 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, joro@...tes.org,
 suravee.suthikulpanit@....com, thomas.lendacky@....com,
 Sairaj.ArunKodilkar@....com, herbert@...dor.apana.org.au
Cc: seanjc@...gle.com, pbonzini@...hat.com, will@...nel.org,
 robin.murphy@....com, john.allen@....com, davem@...emloft.net,
 michael.roth@....com, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 linux-crypto@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v5 4/4] iommu/amd: Skip enabling command/event buffers for
 kdump



On 7/31/2025 3:26 AM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> After a panic if SNP is enabled in the previous kernel then the kdump
> kernel boots with IOMMU SNP enforcement still enabled.
> 
> IOMMU command buffers and event buffer registers remain locked and
> exclusive to the previous kernel. Attempts to enable command and event
> buffers in the kdump kernel will fail, as hardware ignores writes to
> the locked MMIO registers as per AMD IOMMU spec Section 2.12.2.1.
> 
> Skip enabling command buffers and event buffers for kdump boot as they
> are already enabled in the previous kernel.
> 
> Tested-by: Sairaj Kodilkar <sarunkod@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>

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


-Vasant