Re: [PATCH v4 4/4] iommu/amd: Skip enabling command/event buffers for kdump

[Sairaj Kodilkar]

On 7/22/2025 3:23 AM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
>
> 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.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Tested-by: Sairaj Kodilkar <sarunkod@xxxxxxx>