linux-kernel - Re: [PATCH] KVM: arm64: Check cpu_has_spe() before initializing PMSCR

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Message-ID: <aOVckTSJET5ORY1n@linux.dev>
Date: Tue, 7 Oct 2025 11:31:45 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
Cc: maz@...nel.org, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, catalin.marinas@....com, will@...nel.org,
	alexandru.elisei@....com, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Check cpu_has_spe() before initializing
 PMSCR_EL1 in VHE

Hi Mukesh,

I find it a bit odd to refer to cpu_has_spe() in the shortlog, which
doesn't exist prior to this patch.

On Tue, Oct 07, 2025 at 11:53:56PM +0530, Mukesh Ojha wrote:
> commit efad60e46057 ("KVM: arm64: Initialize PMSCR_EL1 when in VHE")
> initializes PMSCR_EL1 to 0 which is making the boot up stuck when KVM
> runs in VHE mode and reverting the change is fixing the issue.
> 
> [    2.967447] RPC: Registered tcp NFSv4.1 backchannel transport module.
> [    2.974061] PCI: CLS 0 bytes, default 64
> [    2.978171] Unpacking initramfs...
> [    2.982889] kvm [1]: nv: 568 coarse grained trap handlers
> [    2.988573] kvm [1]: IPA Size Limit: 40 bits
> 
> Lets guard the change with cpu_has_spe() check so that it only affects
> the cpu which has SPE feature supported.

This could benefit from being spelled out a bit more. In both cases we
check for the presence of FEAT_SPE, however I believe the issue you
observe is EL3 hasn't delegated ownership of the Profiling Buffer to
Non-secure nor does it reinject an UNDEF in response to the sysreg trap.

I agree that the change is correct but the rationale needs to be clear.

Thanks,
Oliver