Messages in this thread | | | Date | Mon, 24 Jul 2023 21:50:20 +0800 | Subject | Re: [PATCH v4 10/20] KVM:x86: Make guest supervisor states as non-XSAVE managed | From | "Yang, Weijiang" <> |
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On 7/24/2023 4:26 PM, Chao Gao wrote: > On Thu, Jul 20, 2023 at 11:03:42PM -0400, Yang Weijiang wrote: >> +static void kvm_save_cet_supervisor_ssp(struct kvm_vcpu *vcpu) >> +{ >> + preempt_disable(); > what's the purpose of disabling preemption?
Thanks!
These preempt_disable/enable() becomes unnecessary due to the PLx_SSP handling
in sched_in/out(). Will remove them.
> >> + if (unlikely(guest_can_use(vcpu, X86_FEATURE_SHSTK))) { >> + rdmsrl(MSR_IA32_PL0_SSP, vcpu->arch.cet_s_ssp[0]); >> + rdmsrl(MSR_IA32_PL1_SSP, vcpu->arch.cet_s_ssp[1]); >> + rdmsrl(MSR_IA32_PL2_SSP, vcpu->arch.cet_s_ssp[2]); >> + /* >> + * Omit reset to host PL{1,2}_SSP because Linux will never use >> + * these MSRs. >> + */ >> + wrmsrl(MSR_IA32_PL0_SSP, 0); > You don't need to reset the MSR because current host doesn't enable SSS > and leaving guest value in the MSR won't affect host behavior.
Yes, I just want to make the host PLx_SSPs as clean as possible.
> >> + } >> + preempt_enable(); >> +} >> + >> +static void kvm_reload_cet_supervisor_ssp(struct kvm_vcpu *vcpu) >> +{ >> + preempt_disable(); >> + if (unlikely(guest_can_use(vcpu, X86_FEATURE_SHSTK))) { >> + wrmsrl(MSR_IA32_PL0_SSP, vcpu->arch.cet_s_ssp[0]); >> + wrmsrl(MSR_IA32_PL1_SSP, vcpu->arch.cet_s_ssp[1]); >> + wrmsrl(MSR_IA32_PL2_SSP, vcpu->arch.cet_s_ssp[2]); >> + } >> + preempt_enable(); >> +} > save/load PLx_SSP in kvm_sched_in/out() and in VCPU_RUN ioctl is sub-optimal. > > How about: > 1. expose kvm_save/reload_cet_supervisor_ssp() > 2. reload guest PLx_SSP in {vmx,svm}_prepare_switch_to_guest() > 3. save guest PLx_SSP in vmx_prepare_switch_to_host() and > svm_prepare_host_switch()? > > this way existing svm/vmx->guest_state_loaded can help to reduce a lot of > unnecessary PLx_SSP MSR accesses.
Nice suggestion! It looks workable. I'll try this, thanks!
> >> + >> int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) >> { >> struct kvm_queued_exception *ex = &vcpu->arch.exception; >> @@ -11222,6 +11249,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) >> kvm_sigset_activate(vcpu); >> kvm_run->flags = 0; >> kvm_load_guest_fpu(vcpu); >> + kvm_reload_cet_supervisor_ssp(vcpu); >> >> kvm_vcpu_srcu_read_lock(vcpu); >> if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) { >> @@ -11310,6 +11338,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) >> r = vcpu_run(vcpu); >> >> out: >> + kvm_save_cet_supervisor_ssp(vcpu); >> kvm_put_guest_fpu(vcpu); >> if (kvm_run->kvm_valid_regs) >> store_regs(vcpu); >> @@ -12398,9 +12427,17 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) >> pmu->need_cleanup = true; >> kvm_make_request(KVM_REQ_PMU, vcpu); >> } >> + >> + kvm_reload_cet_supervisor_ssp(vcpu); >> + >> static_call(kvm_x86_sched_in)(vcpu, cpu); >> } >> >> +void kvm_arch_sched_out(struct kvm_vcpu *vcpu, int cpu) >> +{ > @cpu its meaning isn't clear and isn't used and ... Yes, I should have removed it. > >> + kvm_save_cet_supervisor_ssp(vcpu); >> +} >> + >> void kvm_arch_free_vm(struct kvm *kvm) >> { >> kfree(to_kvm_hv(kvm)->hv_pa_pg); >> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >> index d90331f16db1..b3032a5f0641 100644 >> --- a/include/linux/kvm_host.h >> +++ b/include/linux/kvm_host.h >> @@ -1423,6 +1423,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu, >> int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu); >> >> void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu); >> +void kvm_arch_sched_out(struct kvm_vcpu *vcpu, int cpu); >> >> void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu); >> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu); >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 66c1447d3c7f..42f28e8905e1 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -5885,6 +5885,7 @@ static void kvm_sched_out(struct preempt_notifier *pn, >> { >> struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); >> >> + kvm_arch_sched_out(vcpu, 0); > passing 0 always looks problematic. Can you elaborate? I have no intent to use @cpu now. >> if (current->on_rq) { >> WRITE_ONCE(vcpu->preempted, true); >> WRITE_ONCE(vcpu->ready, true); >> -- >> 2.27.0 >>
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