2024-03-26 08:12:39

by Ravi Bangoria

Subject: [PATCH] KVM: SEV-ES: Don't intercept MSR_IA32_DEBUGCTLMSR for SEV-ES guests

Currently, LBR Virtualization is dynamically enabled and disabled for
a vcpu by intercepting writes to MSR_IA32_DEBUGCTLMSR. This helps by
avoiding unnecessary save/restore of LBR MSRs when nobody is using it
in the guest. However, SEV-ES guest mandates LBR Virtualization to be
_always_ ON[1] and thus this dynamic toggling doesn't work for SEV-ES
guest, in fact it results into fatal error:

SEV-ES guest on Zen3, kvm-amd.ko loaded with lbrv=1

[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.

[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")
Signed-off-by: Ravi Bangoria <[email protected]>
---
arch/x86/kvm/svm/sev.c | 1 +
arch/x86/kvm/svm/svm.c | 1 +
arch/x86/kvm/svm/svm.h | 2 +-
3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index a8ce5226b3b5..ef932a7ff9bd 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3073,6 +3073,7 @@ 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_DEBUGCTLMSR, 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);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e90b429c84f1..5a82135ae84e 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 },
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 8ef95139cd24..7a1b60bcebff 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;
--
2.44.0

2024-03-26 09:12:23

by Nikunj A. Dadhania

Subject: Re: [PATCH] KVM: SEV-ES: Don't intercept MSR_IA32_DEBUGCTLMSR for SEV-ES guests

On 3/26/2024 1:41 PM, Ravi Bangoria wrote:
> Currently, LBR Virtualization is dynamically enabled and disabled for
> a vcpu by intercepting writes to MSR_IA32_DEBUGCTLMSR. This helps by
> avoiding unnecessary save/restore of LBR MSRs when nobody is using it
> in the guest. However, SEV-ES guest mandates LBR Virtualization to be
> _always_ ON[1] and thus this dynamic toggling doesn't work for SEV-ES
> guest, in fact it results into fatal error:
>
> SEV-ES guest on Zen3, kvm-amd.ko loaded with lbrv=1
>
> [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.
>
> [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")
> Signed-off-by: Ravi Bangoria <[email protected]>

Reviewed-by: Nikunj A Dadhania <[email protected]>

> ---
> arch/x86/kvm/svm/sev.c | 1 +
> arch/x86/kvm/svm/svm.c | 1 +
> arch/x86/kvm/svm/svm.h | 2 +-
> 3 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a8ce5226b3b5..ef932a7ff9bd 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3073,6 +3073,7 @@ 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_DEBUGCTLMSR, 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);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index e90b429c84f1..5a82135ae84e 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 },
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 8ef95139cd24..7a1b60bcebff 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;

2024-03-26 13:02:49

by Tom Lendacky

Subject: Re: [PATCH] KVM: SEV-ES: Don't intercept MSR_IA32_DEBUGCTLMSR for SEV-ES guests

On 3/26/24 03:11, Ravi Bangoria wrote:
> Currently, LBR Virtualization is dynamically enabled and disabled for
> a vcpu by intercepting writes to MSR_IA32_DEBUGCTLMSR. This helps by
> avoiding unnecessary save/restore of LBR MSRs when nobody is using it
> in the guest. However, SEV-ES guest mandates LBR Virtualization to be
> _always_ ON[1] and thus this dynamic toggling doesn't work for SEV-ES
> guest, in fact it results into fatal error:
>
> SEV-ES guest on Zen3, kvm-amd.ko loaded with lbrv=1
>
> [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.

Adding something to the commit message that this MSR is fully virtualized
(swap type A) would be good to have. Aside from that.

Reviewed-by: Tom Lendacky <[email protected]>

>
> [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")
> Signed-off-by: Ravi Bangoria <[email protected]>
> ---
> arch/x86/kvm/svm/sev.c | 1 +
> arch/x86/kvm/svm/svm.c | 1 +
> arch/x86/kvm/svm/svm.h | 2 +-
> 3 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a8ce5226b3b5..ef932a7ff9bd 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3073,6 +3073,7 @@ 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_DEBUGCTLMSR, 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);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index e90b429c84f1..5a82135ae84e 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 },
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 8ef95139cd24..7a1b60bcebff 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;