[03/22] KVM: x86: Support IBPB_BRTYPE and SBPB
Commit Message
The IBPB_BRTYPE and SBPB CPUID bits aren't set by HW.
From the AMD SRSO whitepaper:
"Hypervisor software should synthesize the value of both the
IBPB_BRTYPE and SBPB CPUID bits on these platforms for use by guest
software."
These bits are already set during kernel boot. Manually propagate them
to the guest.
Also, propagate PRED_CMD_SBPB writes.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
arch/x86/kvm/cpuid.c | 4 ++++
arch/x86/kvm/x86.c | 9 +++++----
2 files changed, 9 insertions(+), 4 deletions(-)
Comments
On Thu, Aug 24, 2023 at 09:39:03AM -0700, Sean Christopherson wrote:
> > Also, since you're clearly more qualified to write this patch than me,
> > can I nominate you to do so? :-)
>
> Sorry, didn't mean to ghost you. I can write the patch, but I won't get to it
> before next week some time.
No worries, I'll pull in your code (with a reserved_bit fix) for my v2.
@@ -729,6 +729,10 @@ void kvm_set_cpu_caps(void)
F(NULL_SEL_CLR_BASE) | F(AUTOIBRS) | 0 /* PrefetchCtlMsr */
);
+ if (cpu_feature_enabled(X86_FEATURE_SBPB))
+ kvm_cpu_cap_set(X86_FEATURE_SBPB);
+ if (cpu_feature_enabled(X86_FEATURE_IBPB_BRTYPE))
+ kvm_cpu_cap_set(X86_FEATURE_IBPB_BRTYPE);
if (cpu_feature_enabled(X86_FEATURE_SRSO_NO))
kvm_cpu_cap_set(X86_FEATURE_SRSO_NO);
@@ -3676,12 +3676,13 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (!msr_info->host_initiated && !guest_has_pred_cmd_msr(vcpu))
return 1;
- if (!boot_cpu_has(X86_FEATURE_IBPB) || (data & ~PRED_CMD_IBPB))
+ if (boot_cpu_has(X86_FEATURE_IBPB) && data == PRED_CMD_IBPB)
+ wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
+ else if (boot_cpu_has(X86_FEATURE_SBPB) && data == PRED_CMD_SBPB)
+ wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_SBPB);
+ else if (data)
return 1;
- if (!data)
- break;
- wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
break;
case MSR_IA32_FLUSH_CMD:
if (!msr_info->host_initiated &&