linux-kernel - Re: [PATCH v6 40/44] KVM: VMX: Set MSR index auto-load entry if and only if entry is "new"

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Message-ID: <c2562f0b-9d73-479d-acaf-27da2fbe0c1e@linux.intel.com>
Date: Mon, 8 Dec 2025 17:35:13 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oupton@...nel.org>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
 Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
 Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Xin Li <xin@...or.com>, "H. Peter Anvin" <hpa@...or.com>,
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
 kvm@...r.kernel.org, loongarch@...ts.linux.dev,
 kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Mingwei Zhang <mizhang@...gle.com>, Xudong Hao <xudong.hao@...el.com>,
 Sandipan Das <sandipan.das@....com>,
 Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
 Manali Shukla <manali.shukla@....com>, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v6 40/44] KVM: VMX: Set MSR index auto-load entry if and
 only if entry is "new"

On 12/6/2025 8:17 AM, Sean Christopherson wrote:
> When adding an MSR to the auto-load lists, update the MSR index in the
> list entry if and only if a new entry is being inserted, as 'i' can only
> be non-negative if vmx_find_loadstore_msr_slot() found an entry with the
> MSR's index.  Unnecessarily setting the index is benign, but it makes it
> harder to see that updating the value is necessary even when an existing
> entry for the MSR was found.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 2c50ebf4ff1b..be2a2580e8f1 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1141,16 +1141,16 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  
>  	if (i < 0) {
>  		i = m->guest.nr++;
> +		m->guest.val[i].index = msr;
>  		vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->guest.nr);
>  	}
> -	m->guest.val[i].index = msr;
>  	m->guest.val[i].value = guest_val;
>  
>  	if (j < 0) {
>  		j = m->host.nr++;
> +		m->host.val[j].index = msr;
>  		vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->host.nr);
>  	}
> -	m->host.val[j].index = msr;
>  	m->host.val[j].value = host_val;
>  }
>  

Reviewed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>