linux-kernel - Re: [PATCH v6 35/44] KVM: VMX: Drop intermediate "guest" field from msr

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Message-ID: <0237b3eb-87f5-4758-b704-9f8d525f1f15@linux.intel.com>
Date: Mon, 8 Dec 2025 17:14:56 +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 35/44] KVM: VMX: Drop intermediate "guest" field from
 msr_autostore


On 12/6/2025 8:17 AM, Sean Christopherson wrote:
> Drop the intermediate "guest" field from vcpu_vmx.msr_autostore as the
> value saved on VM-Exit isn't guaranteed to be the guest's value, it's
> purely whatever is in hardware at the time of VM-Exit.  E.g. KVM's only
> use of the store list at the momemnt is to snapshot TSC at VM-Exit, and
> the value saved is always the raw TSC even if TSC-offseting and/or
> TSC-scaling is enabled for the guest.
>
> And unlike msr_autoload, there is no need differentiate between "on-entry"
> and "on-exit".
>
> No functional change intended.
>
> Cc: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 10 +++++-----
>  arch/x86/kvm/vmx/vmx.c    |  2 +-
>  arch/x86/kvm/vmx/vmx.h    |  4 +---
>  3 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 729cc1f05ac8..486789dac515 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -1076,11 +1076,11 @@ static bool nested_vmx_get_vmexit_msr_value(struct kvm_vcpu *vcpu,
>  	 * VM-exit in L0, use the more accurate value.
>  	 */
>  	if (msr_index == MSR_IA32_TSC) {
> -		int i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
> +		int i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore,
>  						    MSR_IA32_TSC);
>  
>  		if (i >= 0) {
> -			u64 val = vmx->msr_autostore.guest.val[i].value;
> +			u64 val = vmx->msr_autostore.val[i].value;
>  
>  			*data = kvm_read_l1_tsc(vcpu, val);
>  			return true;
> @@ -1167,7 +1167,7 @@ static void prepare_vmx_msr_autostore_list(struct kvm_vcpu *vcpu,
>  					   u32 msr_index)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> -	struct vmx_msrs *autostore = &vmx->msr_autostore.guest;
> +	struct vmx_msrs *autostore = &vmx->msr_autostore;
>  	bool in_vmcs12_store_list;
>  	int msr_autostore_slot;
>  	bool in_autostore_list;
> @@ -2366,7 +2366,7 @@ static void prepare_vmcs02_constant_state(struct vcpu_vmx *vmx)
>  	 * addresses are constant (for vmcs02), the counts can change based
>  	 * on L2's behavior, e.g. switching to/from long mode.
>  	 */
> -	vmcs_write64(VM_EXIT_MSR_STORE_ADDR, __pa(vmx->msr_autostore.guest.val));
> +	vmcs_write64(VM_EXIT_MSR_STORE_ADDR, __pa(vmx->msr_autostore.val));
>  	vmcs_write64(VM_EXIT_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.host.val));
>  	vmcs_write64(VM_ENTRY_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.guest.val));
>  
> @@ -2704,7 +2704,7 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
>  	 */
>  	prepare_vmx_msr_autostore_list(&vmx->vcpu, MSR_IA32_TSC);
>  
> -	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, vmx->msr_autostore.guest.nr);
> +	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, vmx->msr_autostore.nr);
>  	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.host.nr);
>  	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
>  
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 62ba2a2b9e98..23c92c41fd83 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6567,7 +6567,7 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
>  	if (vmcs_read32(VM_ENTRY_MSR_LOAD_COUNT) > 0)
>  		vmx_dump_msrs("guest autoload", &vmx->msr_autoload.guest);
>  	if (vmcs_read32(VM_EXIT_MSR_STORE_COUNT) > 0)
> -		vmx_dump_msrs("guest autostore", &vmx->msr_autostore.guest);
> +		vmx_dump_msrs("autostore", &vmx->msr_autostore);
>  
>  	if (vmentry_ctl & VM_ENTRY_LOAD_CET_STATE)
>  		pr_err("S_CET = 0x%016lx, SSP = 0x%016lx, SSP TABLE = 0x%016lx\n",
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index d7a96c84371f..4ce653d729ca 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -245,9 +245,7 @@ struct vcpu_vmx {
>  		struct vmx_msrs host;
>  	} msr_autoload;
>  
> -	struct msr_autostore {
> -		struct vmx_msrs guest;
> -	} msr_autostore;
> +	struct vmx_msrs msr_autostore;
>  
>  	struct {
>  		int vm86_active;

LGTM.

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