Messages in this thread Patch in this message |  | | From | Paolo Bonzini <> | | Subject | [PATCH 7/7] KVM: VMX: replace vmx_spec_ctrl_restore_host with RESTORE_HOST_SPEC_CTRL_BODY | | Date | Wed, 8 Apr 2026 14:22:13 -0400 |
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Reuse the same assembly as SVM, just with alternatives instead of cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS).
Due to the dearth of registers in 32-bit x86, save/restore %eax across the restoring sequence, keeping it simple; the main alternative would be to leave vmx and flags on the stack, avoiding the need to read flags from %ebx. It's not really measurable difference.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- arch/x86/kvm/vmenter.h | 4 ++-- arch/x86/kvm/vmx/vmenter.S | 25 +++++++++++++++---------- arch/x86/kvm/vmx/vmx.c | 25 ------------------------- arch/x86/kvm/vmx/vmx.h | 1 - 4 files changed, 17 insertions(+), 38 deletions(-)
diff --git a/arch/x86/kvm/vmenter.h b/arch/x86/kvm/vmenter.h index e746e1328d3f..d822dafc75f7 100644 --- a/arch/x86/kvm/vmenter.h +++ b/arch/x86/kvm/vmenter.h @@ -55,7 +55,7 @@ #ifdef CONFIG_X86_64 mov PER_CPU_VAR(x86_spec_ctrl_current), %rdx cmp \guest_spec_ctrl, %rdx - je \label + ALTERNATIVE "", __stringify(je \label), X86_FEATURE_KERNEL_IBRS movl %edx, %eax shr $32, %rdx #else @@ -66,7 +66,7 @@ mov 4 + \guest_spec_ctrl, %edi xor %edx, %edi or %edi, %esi - je \label + ALTERNATIVE "", __stringify(je \label), X86_FEATURE_KERNEL_IBRS #endif wrmsr .endm diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S index f3240a3ff8f5..c0574d68ff45 100644 --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -105,9 +105,9 @@ SYM_FUNC_START(__vmx_vcpu_run) * Unlike AMD there's no V_SPEC_CTRL here, so do not leave the body * out of line. Clobbers RAX, RCX, RDX, RSI. */ - ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL - RESTORE_GUEST_SPEC_CTRL_BODY VMX_spec_ctrl(%_ASM_DI), .Lspec_ctrl_done -.Lspec_ctrl_done: + ALTERNATIVE "jmp .Lspec_ctrl_guest_done", "", X86_FEATURE_MSR_SPEC_CTRL + RESTORE_GUEST_SPEC_CTRL_BODY VMX_spec_ctrl(%_ASM_DI), .Lspec_ctrl_guest_done +.Lspec_ctrl_guest_done: /* * Since vmentry is serializing on affected CPUs, there's no need for @@ -252,16 +252,21 @@ SYM_INNER_LABEL_ALIGN(vmx_vmexit, SYM_L_GLOBAL) FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT,\ X86_FEATURE_RSB_VMEXIT_LITE - pop %_ASM_ARG2 /* @flags */ - pop %_ASM_ARG1 /* @vmx */ - - call vmx_spec_ctrl_restore_host - - CLEAR_BRANCH_HISTORY_VMEXIT - /* Put return value in AX */ mov %_ASM_BX, %_ASM_AX + pop %_ASM_BX /* @flags */ + pop %_ASM_DI /* @vmx */ + + /* Clobbers RAX, RCX, RDX, RSI. */ + ALTERNATIVE "jmp .Lspec_ctrl_host_done", "", X86_FEATURE_MSR_SPEC_CTRL + push %_ASM_AX + RESTORE_HOST_SPEC_CTRL_BODY VMX_spec_ctrl(%_ASM_DI), %ebx, .Lspec_ctrl_host_done + pop %_ASM_AX +.Lspec_ctrl_host_done: + + CLEAR_BRANCH_HISTORY_VMEXIT + pop %_ASM_BX #ifdef CONFIG_X86_64 pop %r12 diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index ef0de3cc0bc2..84a5441142fc 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7497,31 +7497,6 @@ void noinstr vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp) } } -void noinstr vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx, - unsigned int flags) -{ - u64 hostval = this_cpu_read(x86_spec_ctrl_current); - - if (!cpu_feature_enabled(X86_FEATURE_MSR_SPEC_CTRL)) - return; - - if (flags & KVM_ENTER_SAVE_SPEC_CTRL) - vmx->spec_ctrl = native_rdmsrq(MSR_IA32_SPEC_CTRL); - - /* - * If the guest/host SPEC_CTRL values differ, restore the host value. - * - * For legacy IBRS, the IBRS bit always needs to be written after - * transitioning from a less privileged predictor mode, regardless of - * whether the guest/host values differ. - */ - if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) || - vmx->spec_ctrl != hostval) - native_wrmsrq(MSR_IA32_SPEC_CTRL, hostval); - - barrier_nospec(); -} - static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu, bool force_immediate_exit) { diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index 9cb5a205f19d..fec85c739fad 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -370,7 +370,6 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu); struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr); void pt_update_intercept_for_msr(struct kvm_vcpu *vcpu); void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp); -void vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx, unsigned int flags); unsigned int __vmx_vcpu_enter_flags(struct vcpu_vmx *vmx); bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned int flags); void vmx_ept_load_pdptrs(struct kvm_vcpu *vcpu); -- 2.52.0
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