As documented in APM[1], LBR Virtualization must be enabled for SEV-ES
guests. Although KVM currently enforces LBRV for SEV-ES guests, there
are multiple issues with it:
o MSR_IA32_DEBUGCTLMSR is still intercepted. Since MSR_IA32_DEBUGCTLMSR
interception is used to dynamically toggle LBRV for performance reasons,
this can be fatal for SEV-ES guests. For ex SEV-ES guest on Zen3:
[guest ~]# wrmsr 0x1d9 0x4
KVM: entry failed, hardware error 0xffffffff
EAX=00000004 EBX=00000000 ECX=000001d9 EDX=00000000
Fix this by never intercepting MSR_IA32_DEBUGCTLMSR for SEV-ES guests.
No additional save/restore logic is required since MSR_IA32_DEBUGCTLMSR
is of swap type A.
o KVM will disable LBRV if userspace sets MSR_IA32_DEBUGCTLMSR before the
VMSA is encrypted. Fix this by moving LBRV enablement code post VMSA
encryption.
[1]: AMD64 Architecture Programmer's Manual Pub. 40332, Rev. 4.07 - June
2023, Vol 2, 15.35.2 Enabling SEV-ES.
https://bugzilla.kernel.org/attachment.cgi?id=304653
Fixes: 376c6d285017 ("KVM: SVM: Provide support for SEV-ES vCPU creation/loading")
Co-developed-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
---
arch/x86/kvm/svm/sev.c | 13 ++++++++-----
arch/x86/kvm/svm/svm.c | 8 +++++++-
arch/x86/kvm/svm/svm.h | 3 ++-
3 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 8345a5098ab7..7d401f8a3001 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -851,6 +851,14 @@ static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu,
*/
fpstate_set_confidential(&vcpu->arch.guest_fpu);
vcpu->arch.guest_state_protected = true;
+
+ /*
+ * SEV-ES guest mandates LBR Virtualization to be _always_ ON. Enable it
+ * only after setting guest_state_protected because KVM_SET_MSRS allows
+ * dynamic toggling of LBRV (for performance reason) on write access to
+ * MSR_IA32_DEBUGCTLMSR when guest_state_protected is not set.
+ */
+ svm_enable_lbrv(vcpu);
return 0;
}
@@ -4279,7 +4287,6 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
struct kvm_vcpu *vcpu = &svm->vcpu;
svm->vmcb->control.nested_ctl |= SVM_NESTED_CTL_SEV_ES_ENABLE;
- svm->vmcb->control.virt_ext |= LBR_CTL_ENABLE_MASK;
/*
* An SEV-ES guest requires a VMSA area that is a separate from the
@@ -4331,10 +4338,6 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
/* Clear intercepts on selected MSRs */
set_msr_interception(vcpu, svm->msrpm, MSR_EFER, 1, 1);
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_CR_PAT, 1, 1);
- set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHFROMIP, 1, 1);
- set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHTOIP, 1, 1);
- set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTFROMIP, 1, 1);
- set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTTOIP, 1, 1);
}
void sev_init_vmcb(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index cadf3085f183..bff08729c0e9 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -99,6 +99,7 @@ static const struct svm_direct_access_msrs {
{ .index = MSR_IA32_SPEC_CTRL, .always = false },
{ .index = MSR_IA32_PRED_CMD, .always = false },
{ .index = MSR_IA32_FLUSH_CMD, .always = false },
+ { .index = MSR_IA32_DEBUGCTLMSR, .always = false },
{ .index = MSR_IA32_LASTBRANCHFROMIP, .always = false },
{ .index = MSR_IA32_LASTBRANCHTOIP, .always = false },
{ .index = MSR_IA32_LASTINTFROMIP, .always = false },
@@ -990,7 +991,7 @@ void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
vmcb_mark_dirty(to_vmcb, VMCB_LBR);
}
-static void svm_enable_lbrv(struct kvm_vcpu *vcpu)
+void svm_enable_lbrv(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -1000,6 +1001,9 @@ static void svm_enable_lbrv(struct kvm_vcpu *vcpu)
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTFROMIP, 1, 1);
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTTOIP, 1, 1);
+ if (sev_es_guest(vcpu->kvm))
+ set_msr_interception(vcpu, svm->msrpm, MSR_IA32_DEBUGCTLMSR, 1, 1);
+
/* Move the LBR msrs to the vmcb02 so that the guest can see them. */
if (is_guest_mode(vcpu))
svm_copy_lbrs(svm->vmcb, svm->vmcb01.ptr);
@@ -1009,6 +1013,8 @@ static void svm_disable_lbrv(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
+ KVM_BUG_ON(sev_es_guest(vcpu->kvm), vcpu->kvm);
+
svm->vmcb->control.virt_ext &= ~LBR_CTL_ENABLE_MASK;
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHFROMIP, 0, 0);
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHTOIP, 0, 0);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 2d6c19c55b1a..3424a9577872 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -30,7 +30,7 @@
#define IOPM_SIZE PAGE_SIZE * 3
#define MSRPM_SIZE PAGE_SIZE * 2
-#define MAX_DIRECT_ACCESS_MSRS 47
+#define MAX_DIRECT_ACCESS_MSRS 48
#define MSRPM_OFFSETS 32
extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
extern bool npt_enabled;
@@ -583,6 +583,7 @@ u32 *svm_vcpu_alloc_msrpm(void);
void svm_vcpu_init_msrpm(struct kvm_vcpu *vcpu, u32 *msrpm);
void svm_vcpu_free_msrpm(u32 *msrpm);
void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb);
+void svm_enable_lbrv(struct kvm_vcpu *vcpu);
void svm_update_lbrv(struct kvm_vcpu *vcpu);
int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
--
2.45.1SEV-ES and thus SNP guest mandates LBR Virtualization to be _always_ ON.
Although commit b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization
to the processor") did the correct change for SEV-ES guests, it missed
the SNP. Fix it.
Reported-by: Srikanth Aithal <sraithal@amd.com>
Fixes: b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization to the processor")
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
---
- SNP support was not present while I prepared the original patches and
that lead to this confusion. Sorry about that.
arch/x86/kvm/svm/sev.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7d401f8a3001..57291525e084 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2395,6 +2395,14 @@ static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
}
svm->vcpu.arch.guest_state_protected = true;
+ /*
+ * SEV-ES (and thus SNP) guest mandates LBR Virtualization to
+ * be _always_ ON. Enable it only after setting
+ * guest_state_protected because KVM_SET_MSRS allows dynamic
+ * toggling of LBRV (for performance reason) on write access to
+ * MSR_IA32_DEBUGCTLMSR when guest_state_protected is not set.
+ */
+ svm_enable_lbrv(vcpu);
}
return 0;
--
2.45.1
On 6/5/2024 5:18 PM, Ravi Bangoria wrote:
> SEV-ES and thus SNP guest mandates LBR Virtualization to be _always_ ON.
> Although commit b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization
> to the processor") did the correct change for SEV-ES guests, it missed
> the SNP. Fix it.
>
> Reported-by: Srikanth Aithal <sraithal@amd.com>
> Fixes: b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization to the processor")
> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
> ---
> - SNP support was not present while I prepared the original patches and
> that lead to this confusion. Sorry about that.
>
> arch/x86/kvm/svm/sev.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 7d401f8a3001..57291525e084 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2395,6 +2395,14 @@ static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
> }
>
> svm->vcpu.arch.guest_state_protected = true;
> + /*
> + * SEV-ES (and thus SNP) guest mandates LBR Virtualization to
> + * be _always_ ON. Enable it only after setting
> + * guest_state_protected because KVM_SET_MSRS allows dynamic
> + * toggling of LBRV (for performance reason) on write access to
> + * MSR_IA32_DEBUGCTLMSR when guest_state_protected is not set.
> + */
> + svm_enable_lbrv(vcpu);
> }
>
> return 0;
Tested-by: Srikanth Aithal <sraithal@amd.com>
On Wed, Jun 5, 2024 at 1:49 PM Ravi Bangoria <ravi.bangoria@amd.com> wrote:
>
> SEV-ES and thus SNP guest mandates LBR Virtualization to be _always_ ON.
> Although commit b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization
> to the processor") did the correct change for SEV-ES guests, it missed
> the SNP. Fix it.
>
> Reported-by: Srikanth Aithal <sraithal@amd.com>
> Fixes: b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization to the processor")
> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
> ---
> - SNP support was not present while I prepared the original patches and
> that lead to this confusion. Sorry about that.
No problem, this is a semantic conflict and your original patches will
go in 6.10. Applied to kvm/next.
Paolo
> arch/x86/kvm/svm/sev.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 7d401f8a3001..57291525e084 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2395,6 +2395,14 @@ static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
> }
>
> svm->vcpu.arch.guest_state_protected = true;
> + /*
> + * SEV-ES (and thus SNP) guest mandates LBR Virtualization to
> + * be _always_ ON. Enable it only after setting
> + * guest_state_protected because KVM_SET_MSRS allows dynamic
> + * toggling of LBRV (for performance reason) on write access to
> + * MSR_IA32_DEBUGCTLMSR when guest_state_protected is not set.
> + */
> + svm_enable_lbrv(vcpu);
> }
>
> return 0;
> --
> 2.45.1
>
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