linux-kernel - Re: [PATCH v2 2/4] KVM: arm64: Don't WARN from __pkvm_host_share

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Message-ID: <87jz9d299h.wl-maz@kernel.org>
Date: Tue, 25 Feb 2025 18:02:02 +0000
From: Marc Zyngier <maz@...nel.org>
To: Quentin Perret <qperret@...gle.com>
Cc: Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] KVM: arm64: Don't WARN from __pkvm_host_share_guest()

On Tue, 25 Feb 2025 01:53:25 +0000,
Quentin Perret <qperret@...gle.com> wrote:
> 
> We currently WARN() if the host attempts to share a page that is not in
> an acceptable state with a guest. This isn't strictly necessary and
> makes testing much harder, so drop the WARN and fix the error code.

Are you really fixing the error code? You still seem to return a
-EPERM. I guess this was never reachable thanks to WARN() being a
panic with pKVM?

	M.

> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 19c3c631708c..ae39abc7e604 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -912,7 +912,6 @@ int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu,
>  		if (page->host_share_guest_count)
>  			break;
>  		/* Only host to np-guest multi-sharing is tolerated */
> -		WARN_ON(1);
>  		fallthrough;
>  	default:
>  		ret = -EPERM;
> -- 
> 2.48.1.658.g4767266eb4-goog
> 
> 

-- 
Without deviation from the norm, progress is not possible.