linux-kernel - Re: [PATCH v3 4/6] KVM: SVM: Don't advise the user to do force

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Message-ID: <75n6j3eu6hlfkeug46ekp2po24hiuoia7sju32h73gt4hwjzgk@ddb7t6npdddg>
Date: Fri, 19 Sep 2025 15:56:01 +0530
From: Naveen N Rao <naveen@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/6] KVM: SVM: Don't advise the user to do
 force_avic=y (when x2AVIC is detected)

On Thu, Sep 18, 2025 at 05:21:34PM -0700, Sean Christopherson wrote:
> Don't advise the end user to try to force enable AVIC when x2AVIC is
> reported as supported in CPUID,
			in CPUID but AVIC isn't,

> as forcefully enabling AVIC isn't something
> that should be done lightly.  E.g. some Zen4 client systems hide AVIC but
> leave x2AVIC behind, and while such a configuration is indeed due to buggy
> firmware in the sense the reporting x2AVIC without AVIC is nonsensical,
			^^ that

> KVM has no idea _why_ firmware disabled AVIC in the first place.
> 
> Suggesting that the user try to run with force_avic=y is sketchy even if
> the user explicitly tries to enable AVIC, and will be downright
> irresponsible once KVM starts enabling AVIC by default.  Alternatively,
> KVM could print the message only when the user explicitly asks for AVIC,
> but running with force_avic=y isn't something that should be encouraged
> for random users.  force_avic is a useful knob for developers and perhaps
> even advanced users, but isn't something that KVM should advertise broadly.
> 
> Opportunistically append a newline to the pr_warn() so that it prints out
> immediately, and tweak the message to say that AVIC is unsupported instead
> of disabled (disabled suggests that the kernel/KVM is somehow responsible).
> 
> Suggested-by: Naveen N Rao <naveen@...nel.org>

Suggested-by: Naveen N Rao (AMD) <naveen@...nel.org>

> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/avic.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

Reviewed-by: Naveen N Rao (AMD) <naveen@...nel.org>


- Naveen