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Date: Mon, 14 Dec 2020 16:33:38 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v5 07/34] KVM: SVM: Add required changes to support
intercepts under SEV-ES
On 10/12/20 18:09, Tom Lendacky wrote:
> @@ -2797,7 +2838,27 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
>
> static int wrmsr_interception(struct vcpu_svm *svm)
> {
> - return kvm_emulate_wrmsr(&svm->vcpu);
> + u32 ecx;
> + u64 data;
> +
> + if (!sev_es_guest(svm->vcpu.kvm))
> + return kvm_emulate_wrmsr(&svm->vcpu);
> +
> + ecx = kvm_rcx_read(&svm->vcpu);
> + data = kvm_read_edx_eax(&svm->vcpu);
> + if (kvm_set_msr(&svm->vcpu, ecx, data)) {
> + trace_kvm_msr_write_ex(ecx, data);
> + ghcb_set_sw_exit_info_1(svm->ghcb, 1);
> + ghcb_set_sw_exit_info_2(svm->ghcb,
> + X86_TRAP_GP |
> + SVM_EVTINJ_TYPE_EXEPT |
> + SVM_EVTINJ_VALID);
> + return 1;
> + }
> +
> + trace_kvm_msr_write(ecx, data);
> +
> + return kvm_skip_emulated_instruction(&svm->vcpu);
> }
>
> static int msr_interception(struct vcpu_svm *svm)
This code duplication is ugly, and does not work with userspace MSR
filters too.
But we can instead trap the completion of the MSR read/write to use
ghcb_set_sw_exit_info_1 instead of kvm_inject_gp, with a callback like
static int svm_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
{
if (!sev_es_guest(svm->vcpu.kvm) || !err)
return kvm_complete_insn_gp(&svm->vcpu, err);
ghcb_set_sw_exit_info_1(svm->ghcb, 1);
ghcb_set_sw_exit_info_2(svm->ghcb,
X86_TRAP_GP |
SVM_EVTINJ_TYPE_EXEPT |
SVM_EVTINJ_VALID);
return 1;
}
...
.complete_emulated_msr = svm_complete_emulated_msr,
> @@ -2827,7 +2888,14 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
> static int pause_interception(struct vcpu_svm *svm)
> {
> struct kvm_vcpu *vcpu = &svm->vcpu;
> - bool in_kernel = (svm_get_cpl(vcpu) == 0);
> + bool in_kernel;
> +
> + /*
> + * CPL is not made available for an SEV-ES guest, so just set in_kernel
> + * to true.
> + */
> + in_kernel = (sev_es_guest(svm->vcpu.kvm)) ? true
> + : (svm_get_cpl(vcpu) == 0);
>
> if (!kvm_pause_in_guest(vcpu->kvm))
> grow_ple_window(vcpu);
See below.
> @@ -3273,6 +3351,13 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
> struct vcpu_svm *svm = to_svm(vcpu);
> struct vmcb *vmcb = svm->vmcb;
>
> + /*
> + * SEV-ES guests to not expose RFLAGS. Use the VMCB interrupt mask
> + * bit to determine the state of the IF flag.
> + */
> + if (sev_es_guest(svm->vcpu.kvm))
> + return !(vmcb->control.int_state & SVM_GUEST_INTERRUPT_MASK);
This seems wrong, you have to take into account
SVM_INTERRUPT_SHADOW_MASK as well. Also, even though GIF is not really
used by SEV-ES guests, I think it's nicer to put this check afterwards.
That is:
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 4372e45c8f06..2dd9c9698480 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3247,7 +3247,14 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
if (!gif_set(svm))
return true;
- if (is_guest_mode(vcpu)) {
+ if (sev_es_guest(svm->vcpu.kvm)) {
+ /*
+ * SEV-ES guests to not expose RFLAGS. Use the VMCB interrupt mask
+ * bit to determine the state of the IF flag.
+ */
+ if (!(vmcb->control.int_state & SVM_GUEST_INTERRUPT_MASK))
+ return true;
+ } else if (is_guest_mode(vcpu)) {
/* As long as interrupts are being delivered... */
if ((svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK)
? !(svm->nested.hsave->save.rflags & X86_EFLAGS_IF)
> if (!gif_set(svm))
> return true;
>
> @@ -3458,6 +3543,12 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
> svm->vcpu.arch.nmi_injected = true;
> break;
> case SVM_EXITINTINFO_TYPE_EXEPT:
> + /*
> + * Never re-inject a #VC exception.
> + */
> + if (vector == X86_TRAP_VC)
> + break;
> +
> /*
> * In case of software exceptions, do not reinject the vector,
> * but re-execute the instruction instead. Rewind RIP first
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a3fdc16cfd6f..b6809a2851d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4018,7 +4018,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> {
> int idx;
>
> - if (vcpu->preempted)
> + if (vcpu->preempted && !vcpu->arch.guest_state_protected)
> vcpu->arch.preempted_in_kernel = !kvm_x86_ops.get_cpl(vcpu);
This has to be true, otherwise no directed yield will be done at all:
if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
!kvm_arch_vcpu_in_kernel(vcpu))
continue;
Or more easily, just use in_kernel == false in pause_interception, like
+ /*
+ * CPL is not made available for an SEV-ES guest, therefore
+ * vcpu->arch.preempted_in_kernel can never be true. Just
+ * set in_kernel to false as well.
+ */
+ in_kernel = !sev_es_guest(svm->vcpu.kvm) && svm_get_cpl(vcpu) == 0;
>
> /*
> @@ -8161,7 +8161,9 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu)
> {
> struct kvm_run *kvm_run = vcpu->run;
>
> - kvm_run->if_flag = (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
> + kvm_run->if_flag = (vcpu->arch.guest_state_protected)
> + ? kvm_arch_interrupt_allowed(vcpu)
> + : (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
Here indeed you only want the interrupt allowed bit, not the interrupt
window. But we can just be bold and always set it to true.
- for userspace irqchip, kvm_run->ready_for_interrupt_injection is set
just below and it will always be false if kvm_arch_interrupt_allowed is
false
- for in-kernel APIC, if_flag is documented to be invalid (though it
actually is valid). For split irqchip, they can just use
kvm_run->ready_for_interrupt_injection; for entirely in-kernel interrupt
handling, userspace does not need if_flag at all.
Paolo
> kvm_run->flags = is_smm(vcpu) ? KVM_RUN_X86_SMM : 0;
> kvm_run->cr8 = kvm_get_cr8(vcpu);
> kvm_run->apic_base = kvm_get_apic_base(vcpu);
>
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