linux-kernel - [PATCH v2 2/2] x86: KVM: Advertise AMD's speculation control features

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Message-Id: <20241126094424.943192-3-davydov-max@yandex-team.ru>
Date: Tue, 26 Nov 2024 12:44:24 +0300
From: Maksim Davydov <davydov-max@...dex-team.ru>
To: kvm@...r.kernel.org
Cc: davydov-max@...dex-team.ru,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	babu.moger@....com,
	seanjc@...gle.com,
	mingo@...hat.com,
	bp@...en8.de,
	tglx@...utronix.de,
	dave.hansen@...ux.intel.com,
	hpa@...or.com,
	jmattson@...gle.com,
	pbonzini@...hat.com
Subject: [PATCH v2 2/2] x86: KVM: Advertise AMD's speculation control features

It seems helpful to expose to userspace some speculation control features
from 0x80000008_EBX function:
* 16 bit. IBRS always on. Indicates whether processor prefers that
  IBRS is always on. It simplifies speculation managing.
* 18 bit. IBRS is preferred over software solution. Indicates that
  software mitigations can be replaced with more performant IBRS.
* 19 bit. IBRS provides Same Mode Protection. Indicates that when IBRS
  is set indirect branch predictions are not influenced by any prior
  indirect branches.
* 29 bit. BTC_NO. Indicates that processor isn't affected by branch type
  confusion. It's used during mitigations setting up.
* 30 bit. IBPB clears return address predictor. It's used during
  mitigations setting up.

Signed-off-by: Maksim Davydov <davydov-max@...dex-team.ru>
---
 arch/x86/include/asm/cpufeatures.h | 3 +++
 arch/x86/kvm/cpuid.c               | 5 +++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index f6be4fd2ead0..ba371d364c58 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -340,7 +340,10 @@
 #define X86_FEATURE_AMD_IBPB		(13*32+12) /* Indirect Branch Prediction Barrier */
 #define X86_FEATURE_AMD_IBRS		(13*32+14) /* Indirect Branch Restricted Speculation */
 #define X86_FEATURE_AMD_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_AMD_IBRS_ALWAYS_ON	(13*32+16) /* Indirect Branch Restricted Speculation always-on preferred */
 #define X86_FEATURE_AMD_STIBP_ALWAYS_ON	(13*32+17) /* Single Thread Indirect Branch Predictors always-on preferred */
+#define X86_FEATURE_AMD_IBRS_PREFERRED	(13*32+18) /* Indirect Branch Restricted Speculation is preferred over SW solution */
+#define X86_FEATURE_AMD_IBRS_SMP	(13*32+19) /* Indirect Branch Restricted Speculation provides Same Mode Protection */
 #define X86_FEATURE_AMD_PPIN		(13*32+23) /* "amd_ppin" Protected Processor Inventory Number */
 #define X86_FEATURE_AMD_SSBD		(13*32+24) /* Speculative Store Bypass Disable */
 #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* "virt_ssbd" Virtualized Speculative Store Bypass Disable */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 30ce1bcfc47f..5b2d52913b18 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -754,8 +754,9 @@ void kvm_set_cpu_caps(void)
 	kvm_cpu_cap_mask(CPUID_8000_0008_EBX,
 		F(CLZERO) | F(XSAVEERPTR) |
 		F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) |
-		F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) |
-		F(AMD_PSFD)
+		F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_IBRS_ALWAYS_ON) |
+		F(AMD_STIBP_ALWAYS_ON) | F(AMD_IBRS_PREFERRED) |
+		F(AMD_IBRS_SMP) | F(AMD_PSFD) | F(BTC_NO) | F(AMD_IBPB_RET)
 	);
 
 	/*
-- 
2.34.1