Messages in this thread | | | Date | Mon, 21 Aug 2023 10:34:38 +0100 | From | Andrew Cooper <> | Subject | Re: [PATCH 03/22] KVM: x86: Support IBPB_BRTYPE and SBPB |
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On 21/08/2023 2:19 am, Josh Poimboeuf wrote: > The IBPB_BRTYPE and SBPB CPUID bits aren't set by HW.
"Current hardware".
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c381770bcbf1..dd7472121142 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -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;
SBPB | IBPB is an explicitly permitted combination, but will be rejected by this logic.
FWIW, my patch to Xen went something like:
---8<--- if ( !cp->feat.ibrsb && !cp->extd.ibpb ) goto gp_fault; /* MSR available? */ - if ( val & ~PRED_CMD_IBPB ) + rsvd = ~(PRED_CMD_IBPB | + (cp->extd.sbpb ? PRED_CMD_SBPB : 0)); + + if ( val & rsvd ) goto gp_fault; /* Rsvd bit set? */ if ( v == curr ) ---8<---
~Andrew
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