linux-kernel - [PATCH 7/7] KVM: x86: add SPEC_CTRL and IBPB

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Date:   Mon,  8 Jan 2018 19:08:45 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     jmattson@...gle.com, aliguori@...zon.com, thomas.lendacky@....com,
        dwmw@...zon.co.uk, bp@...en8.de
Subject: [PATCH 7/7] KVM: x86: add SPEC_CTRL and IBPB_SUPPORT to MSR and CPUID lists

Expose them to userspace, now that guests can use them.
I am not adding cpufeatures here to avoid having a kernel
that shows spec_ctrl in /proc/cpuinfo and actually has no
support whatsoever for IBRS/IBPB.  Keep the ugly special-casing
for now, and clean it up once the generic arch/x86/ code
learns about them.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/cpuid.c | 24 +++++++++++++++++++++---
 arch/x86/kvm/x86.c   |  1 +
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 767af697c20c..5f43a5940275 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -397,7 +397,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	/* cpuid 7.0.edx*/
 	const u32 kvm_cpuid_7_0_edx_x86_features =
-		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS);
+		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS) |
+		KF(SPEC_CTRL) | KF(STIBP);
+
+	/* cpuid 0x80000008.edx */
+	const u32 kvm_cpuid_80000008_ebx_x86_features =
+		KF(IBPB_SUPPORT);
 
 	/* all calls to cpuid_count() should be made on the same cpu */
 	get_cpu();
@@ -483,7 +488,14 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 			if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
 				entry->ecx &= ~F(PKU);
 			entry->edx &= kvm_cpuid_7_0_edx_x86_features;
-			entry->edx &= get_scattered_cpuid_leaf(7, 0, CPUID_EDX);
+			/*
+			 * FIXME: the special casing of SPEC_CTRL and STIBP
+			 * can be removed once they become regular
+			 * cpufeatures.
+			 */
+			entry->edx &= (
+				get_scattered_cpuid_leaf(7, 0, CPUID_EDX) |
+				KF(SPEC_CTRL) | KF(STIBP));
 		} else {
 			entry->ebx = 0;
 			entry->ecx = 0;
@@ -651,7 +663,13 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		if (!g_phys_as)
 			g_phys_as = phys_as;
 		entry->eax = g_phys_as | (virt_as << 8);
-		entry->ebx = entry->edx = 0;
+		/*
+		 * FIXME: mask against cpufeatures, with
+		 * get_scattered_cpuid_leaf(0x80000008, 0, CPUID_EBX),
+		 * once IBPB_SUPPORT becomes a regular cpufeature.
+		 */
+		entry->ebx &= kvm_cpuid_80000008_ebx_x86_features;
+		entry->edx = 0;
 		break;
 	}
 	case 0x80000019:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index daa1918031df..4abb37d9f4d8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1032,6 +1032,7 @@ unsigned int kvm_get_pt_addr_cnt(void)
 	MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
 	MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
 	MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
+	MSR_IA32_SPEC_CTRL,
 };
 
 static unsigned num_msrs_to_save;
-- 
1.8.3.1