Re: [PATCH v6 35/44] KVM: VMX: Drop intermediate "guest" field from msr_autostore

Mi, Dapeng
2025-12-08T09:15:10Z

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@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.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@linux.intel.com>