Move KVM's swapping of PKRU outside of the fastpath loop, as there is no KVM code anywhere in the fastpath that accesses guest/userspace memory, i.e. that can consume protection keys. As documented by commit 1be0e61c1f25 ("KVM, pkeys: save/restore PKRU when guest/host switches"), KVM just needs to ensure the host's PKRU is loaded when KVM (or the kernel at-large) may access userspace memory. And at the time of commit 1be0e61c1f25, KVM didn't have a fastpath, and PKU was strictly contained to VMX, i.e. there was no reason to swap PKRU outside of vmx_vcpu_run(). Over time, the "need" to swap PKRU close to VM-Enter was likely falsely solidified by the association with XFEATUREs in commit 37486135d3a7 ("KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c"), and XFEATURE swapping was in turn moved close to VM-Enter/VM-Exit as a KVM hack-a-fix ution for an #MC handler bug by commit 1811d979c716 ("x86/kvm: move kvm_load/put_guest_xcr0 into atomic context"). Deferring the PKRU loads shaves ~40 cycles off the fastpath for Intel, and ~60 cycles for AMD. E.g. using INVD in KVM-Unit-Test's vmexit.c, with extra hacks to enable CR4.PKE and PKRU=(-1u & ~0x3), latency numbers for AMD Turin go from ~1560 => ~1500, and for Intel Emerald Rapids, go from ~810 => ~770. Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/svm.c | 2 -- arch/x86/kvm/vmx/vmx.c | 4 ---- arch/x86/kvm/x86.c | 14 ++++++++++---- arch/x86/kvm/x86.h | 2 -- 4 files changed, 10 insertions(+), 12 deletions(-) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index e8b158f73c79..e1fb853c263c 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4260,7 +4260,6 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) svm_set_dr6(vcpu, DR6_ACTIVE_LOW); clgi(); - kvm_load_guest_xsave_state(vcpu); /* * Hardware only context switches DEBUGCTL if LBR virtualization is @@ -4303,7 +4302,6 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) vcpu->arch.host_debugctl != svm->vmcb->save.dbgctl) update_debugctlmsr(vcpu->arch.host_debugctl); - kvm_load_host_xsave_state(vcpu); stgi(); /* Any pending NMI will happen here */ diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 123dae8cf46b..55d637cea84a 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7465,8 +7465,6 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) vmx_set_interrupt_shadow(vcpu, 0); - kvm_load_guest_xsave_state(vcpu); - pt_guest_enter(vmx); atomic_switch_perf_msrs(vmx); @@ -7510,8 +7508,6 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags) pt_guest_exit(vmx); - kvm_load_host_xsave_state(vcpu); - if (is_guest_mode(vcpu)) { /* * Track VMLAUNCH/VMRESUME that have made past guest state diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b5c2879e3330..6924006f0796 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1233,7 +1233,7 @@ static void kvm_load_host_xfeatures(struct kvm_vcpu *vcpu) } } -void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu) +static void kvm_load_guest_pkru(struct kvm_vcpu *vcpu) { if (vcpu->arch.guest_state_protected) return; @@ -1244,9 +1244,8 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu) kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) wrpkru(vcpu->arch.pkru); } -EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_load_guest_xsave_state); -void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu) +static void kvm_load_host_pkru(struct kvm_vcpu *vcpu) { if (vcpu->arch.guest_state_protected) return; @@ -1259,7 +1258,6 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu) wrpkru(vcpu->arch.host_pkru); } } -EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_load_host_xsave_state); #ifdef CONFIG_X86_64 static inline u64 kvm_guest_supported_xfd(struct kvm_vcpu *vcpu) @@ -11331,6 +11329,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) guest_timing_enter_irqoff(); + /* + * Swap PKRU with hardware breakpoints disabled to minimize the number + * of flows where non-KVM code can run with guest state loaded. + */ + kvm_load_guest_pkru(vcpu); + for (;;) { /* * Assert that vCPU vs. VM APICv state is consistent. An APICv @@ -11359,6 +11363,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) ++vcpu->stat.exits; } + kvm_load_host_pkru(vcpu); + /* * Do this here before restoring debug registers on the host. And * since we do this before handling the vmexit, a DR access vmexit diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index f3dc77f006f9..24c754b0db2e 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -622,8 +622,6 @@ static inline void kvm_machine_check(void) #endif } -void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu); -void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu); int kvm_spec_ctrl_test_value(u64 value); int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r, struct x86_exception *e); -- 2.51.1.930.gacf6e81ea2-goog