linux-kernel - Re: [PATCH v4 2/4] iommu/amd: Reuse device table for kdump

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Message-ID: <90529f27-6e64-4756-9999-b572621b8d6d@amd.com>
Date: Fri, 25 Jul 2025 15:59:37 +0530
From: Sairaj Kodilkar <sarunkod@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, <joro@...tes.org>,
	<suravee.suthikulpanit@....com>, <thomas.lendacky@....com>,
	<Sairaj.ArunKodilkar@....com>, <Vasant.Hegde@....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 v4 2/4] iommu/amd: Reuse device table for kdump



On 7/22/2025 3:23 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 device table register is locked and exclusive to the previous
> kernel. Attempts to copy old device table from the previous kernel
> fails in kdump kernel as hardware ignores writes to the locked device
> table base address register as per AMD IOMMU spec Section 2.12.2.1.
> 
> This results in repeated "Completion-Wait loop timed out" errors and a
> second kernel panic: "Kernel panic - not syncing: timer doesn't work
> through Interrupt-remapped IO-APIC".
> 
> Reuse device table instead of copying device table in case of kdump
> boot and remove all copying device table code.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>

Tested-by: Sairaj Kodilkar <sarunkod@....com>