linux-kernel - [PATCH v7 3/7] x86/cpu, kvm: Move the LFENCE_RDTSC / LFENCE always serializing feature

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Message-ID: <20230116230159.1511393-4-kim.phillips@amd.com>
Date:   Mon, 16 Jan 2023 17:01:55 -0600
From:   Kim Phillips <kim.phillips@....com>
To:     <x86@...nel.org>
CC:     Kim Phillips <kim.phillips@....com>,
        Borislav Petkov <bp@...en8.de>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Alexey Kardashevskiy" <aik@....com>, <kvm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v7 3/7] x86/cpu, kvm: Move the LFENCE_RDTSC / LFENCE always serializing feature

The LFENCE_RDTSC / LFENCE always serializing feature was a scattered bit
and open-coded for KVM in __do_cpuid_func().  Add it to its newly added
CPUID leaf 0x80000021 EAX proper, and propagate it in kvm_set_cpu_caps()
instead.  Drop the bit description comments now it's more self-describing.

Also, in amd_init(), don't bother setting DE_CFG[1] any more if we already
have the X86_FEATURE_LFENCE_RDTSC feature (set by hardware).

Whilst there, switch to using the more efficient cpu_feature_enabled()
instead of static_cpu_has().

Signed-off-by: Kim Phillips <kim.phillips@....com>
---
 arch/x86/include/asm/cpufeatures.h | 3 ++-
 arch/x86/kernel/cpu/amd.c          | 2 +-
 arch/x86/kvm/cpuid.c               | 9 ++++-----
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 8255b95a7987..b22b2e8fef00 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -97,7 +97,7 @@
 #define X86_FEATURE_SYSENTER32		( 3*32+15) /* "" sysenter in IA32 userspace */
 #define X86_FEATURE_REP_GOOD		( 3*32+16) /* REP microcode works well */
 #define X86_FEATURE_AMD_LBR_V2		( 3*32+17) /* AMD Last Branch Record Extension Version 2 */
-#define X86_FEATURE_LFENCE_RDTSC	( 3*32+18) /* "" LFENCE synchronizes RDTSC */
+/* FREE, was #define X86_FEATURE_LFENCE_RDTSC		( 3*32+18) "" LFENCE synchronizes RDTSC */
 #define X86_FEATURE_ACC_POWER		( 3*32+19) /* AMD Accumulated Power Mechanism */
 #define X86_FEATURE_NOPL		( 3*32+20) /* The NOPL (0F 1F) instructions */
 #define X86_FEATURE_ALWAYS		( 3*32+21) /* "" Always-present feature */
@@ -430,6 +430,7 @@
 
 /* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word 20 */
 #define X86_FEATURE_NO_NESTED_DATA_BP	(20*32+ 0) /* "" AMD No Nested Data Breakpoints */
+#define X86_FEATURE_LFENCE_RDTSC	(20*32+ 2) /* "" LFENCE always serializing / synchronizes RDTSC */
 
 /*
  * BUG word(s)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index f769d6d08b43..208c2ce8598a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -956,7 +956,7 @@ static void init_amd(struct cpuinfo_x86 *c)
 
 	init_amd_cacheinfo(c);
 
-	if (cpu_has(c, X86_FEATURE_XMM2)) {
+	if (!cpu_has(c, X86_FEATURE_LFENCE_RDTSC) && cpu_has(c, X86_FEATURE_XMM2)) {
 		/*
 		 * Use LFENCE for execution serialization.  On families which
 		 * don't have that MSR, LFENCE is already serializing.
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c9081e3a1b66..d7a13716b7c8 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -742,8 +742,10 @@ void kvm_set_cpu_caps(void)
 		F(SME_COHERENT));
 
 	kvm_cpu_cap_mask(CPUID_8000_0021_EAX,
-		F(NO_NESTED_DATA_BP)
+		F(NO_NESTED_DATA_BP) | F(LFENCE_RDTSC)
 	);
+	if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC))
+		kvm_cpu_cap_set(X86_FEATURE_LFENCE_RDTSC);
 
 	kvm_cpu_cap_mask(CPUID_C000_0001_EDX,
 		F(XSTORE) | F(XSTORE_EN) | F(XCRYPT) | F(XCRYPT_EN) |
@@ -1229,7 +1231,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		cpuid_entry_override(entry, CPUID_8000_0021_EAX);
 		/*
 		 * Pass down these bits:
-		 *    EAX      2      LAS, LFENCE always serializing
 		 *    EAX      6      NSCB, Null selector clear base
 		 *
 		 * Other defined bits are for MSRs that KVM does not expose:
@@ -1239,10 +1240,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		 * KVM doesn't support SMM_CTL.
 		 *   EAX       9     SMM_CTL MSR is not supported
 		 */
-		entry->eax &= BIT(2) | BIT(6);
+		entry->eax &= BIT(6);
 		entry->eax |= BIT(9);
-		if (static_cpu_has(X86_FEATURE_LFENCE_RDTSC))
-			entry->eax |= BIT(2);
 		if (!static_cpu_has_bug(X86_BUG_NULL_SEG))
 			entry->eax |= BIT(6);
 		break;
-- 
2.34.1