linux-kernel - [PATCH] x86: KVM: Add common feature flag for AMD's PSFD

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Date:   Tue, 24 Jan 2023 19:45:19 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: [PATCH] x86: KVM: Add common feature flag for AMD's PSFD

Use a common X86_FEATURE_* flag for AMD's PSFD, and suppress it from
/proc/cpuinfo via the standard method of an empty string instead of
hacking in a one-off "private" #define in KVM.  The request that led to
KVM defining its own flag was really just that the feature not show up
in /proc/cpuinfo, and additional patches+discussions in the interim have
clarified that defining flags in cpufeatures.h purely so that KVM can
advertise features to userspace is ok so long as the kernel already uses
a word to track the associated CPUID leaf.

No functional change intended.

Link: https://lore.kernel.org/all/d1b1e0da-29f0-c443-6c86-9549bbe1c79d@redhat.como
Link: https://lore.kernel.org/all/YxGZH7aOXQF7Pu5q@nazgul.tnic
Link: https://lore.kernel.org/all/Y3O7UYWfOLfJkwM%2F@zn.tnic
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kvm/cpuid.c               | 8 +-------
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 61012476d66e..2acaebc7bb76 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -330,6 +330,7 @@
 #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
 #define X86_FEATURE_AMD_SSB_NO		(13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
 #define X86_FEATURE_CPPC		(13*32+27) /* Collaborative Processor Performance Control */
+#define X86_FEATURE_AMD_PSFD            (13*32+28) /* "" Predictive Store Forwarding Disable */
 #define X86_FEATURE_BTC_NO		(13*32+29) /* "" Not vulnerable to Branch Type Confusion */
 #define X86_FEATURE_BRS			(13*32+31) /* Branch Sampling available */
 
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2a9f1e200dbc..fb2b0e3ecce1 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -59,12 +59,6 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
 	return ret;
 }
 
-/*
- * This one is tied to SSB in the user API, and not
- * visible in /proc/cpuinfo.
- */
-#define KVM_X86_FEATURE_AMD_PSFD	(13*32+28) /* Predictive Store Forwarding Disable */
-
 #define F feature_bit
 
 /* Scattered Flag - For features that are scattered by cpufeatures.h. */
@@ -710,7 +704,7 @@ void kvm_set_cpu_caps(void)
 		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) |
-		__feature_bit(KVM_X86_FEATURE_AMD_PSFD)
+		F(AMD_PSFD)
 	);
 
 	/*

base-commit: 7cb79f433e75b05d1635aefaa851cfcd1cb7dc4f
-- 
2.39.1.456.gfc5497dd1b-goog