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

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Message-ID: <20251008115344.vwt3j24es7u5f6m4@hu-mojha-hyd.qualcomm.com>
Date: Wed, 8 Oct 2025 17:23:44 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Oliver Upton <oliver.upton@...ux.dev>
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

On Tue, Oct 07, 2025 at 11:31:45AM -0700, Oliver Upton wrote:
> 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.

My bad !!
will fix this

> 
> 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.

You are right, writing to SYS_PMSCR is causing an issue.

is it not the right to check if the profiling buffer is implemented
rather than just checking the version ?

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

Will correct it.

> 
> Thanks,
> Oliver

-- 
-Mukesh Ojha