linux-kernel - [PATCH 03/22] KVM: x86: Support IBPB

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Message-ID: <a4d62162bcb501e50b0bb19b748702aa12260615.1692580085.git.jpoimboe@kernel.org>
Date:   Sun, 20 Aug 2023 18:19:00 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, David.Kaplan@....com,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Nikolay Borisov <nik.borisov@...e.com>,
        gregkh@...uxfoundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 03/22] KVM: x86: Support IBPB_BRTYPE and SBPB

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@...nel.org>
---
 arch/x86/kvm/cpuid.c | 4 ++++
 arch/x86/kvm/x86.c   | 9 +++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d3432687c9e6..cdf703eec42d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -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);
 
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;
-		if (!data)
-			break;
 
-		wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
 		break;
 	case MSR_IA32_FLUSH_CMD:
 		if (!msr_info->host_initiated &&
-- 
2.41.0