On Wed, Nov 08, 2023 at 10:29:49AM -0800, Xin Li wrote: >Switch MSR_IA32_FRED_RSP0 between host and guest in >vmx_prepare_switch_to_{host,guest}(). > >MSR_IA32_FRED_RSP0 is used during ring 3 event delivery only, thus >KVM, running on ring 0, can run safely with guest FRED RSP0, i.e., >no need to switch between host/guest FRED RSP0 during VM entry and >exit. > >KVM should switch to host FRED RSP0 before returning to user level, >and switch to guest FRED RSP0 before entering guest mode. > >Tested-by: Shan Kang <shan.kang@xxxxxxxxx> >Signed-off-by: Xin Li <xin3.li@xxxxxxxxx> >--- > arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++++++ > arch/x86/kvm/vmx/vmx.h | 2 ++ > 2 files changed, 19 insertions(+) > >diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >index 41772ecdd368..d00ab9d4c93e 100644 >--- a/arch/x86/kvm/vmx/vmx.c >+++ b/arch/x86/kvm/vmx/vmx.c >@@ -1344,6 +1344,17 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) > } > > wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base); >+ >+ if (cpu_feature_enabled(X86_FEATURE_FRED) && >+ guest_cpuid_has(vcpu, X86_FEATURE_FRED)) { >+ /* >+ * MSR_IA32_FRED_RSP0 is top of task stack, which never changes. >+ * Thus it should be initialized only once. >+ */ >+ if (unlikely(vmx->msr_host_fred_rsp0 == 0)) >+ vmx->msr_host_fred_rsp0 = read_msr(MSR_IA32_FRED_RSP0); >+ wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_guest_fred_rsp0); >+ } > #else > savesegment(fs, fs_sel); > savesegment(gs, gs_sel); >@@ -1388,6 +1399,12 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx) > invalidate_tss_limit(); > #ifdef CONFIG_X86_64 > wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base); >+ >+ if (cpu_feature_enabled(X86_FEATURE_FRED) && >+ guest_cpuid_has(&vmx->vcpu, X86_FEATURE_FRED)) { IIUC, vmx_prepare_switch_to_host() is called from IRQ-disabled context. using guest_cpuid_has() in this context is not desired, see lockdep_assert_irqs_enabled() in cpuid_entry2_find(). >+ vmx->msr_guest_fred_rsp0 = read_msr(MSR_IA32_FRED_RSP0); >+ wrmsrl(MSR_IA32_FRED_RSP0, vmx->msr_host_fred_rsp0); >+ } > #endif > load_fixmap_gdt(raw_smp_processor_id()); > vmx->guest_state_loaded = false; >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h >index f8c02bd37069..328a3447f064 100644 >--- a/arch/x86/kvm/vmx/vmx.h >+++ b/arch/x86/kvm/vmx/vmx.h >@@ -276,6 +276,8 @@ struct vcpu_vmx { > #ifdef CONFIG_X86_64 > u64 msr_host_kernel_gs_base; > u64 msr_guest_kernel_gs_base; >+ u64 msr_host_fred_rsp0; >+ u64 msr_guest_fred_rsp0; resetting guest fred rsp0 to 0 during vcpu reset is missing. > #endif > > u64 spec_ctrl; >-- >2.42.0 > >