linux-kernel - [PATCH 2/7] x86/bugs: Cache the value of MSR_IA32_ARCH

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Message-ID: <9592a18a814368e75f8f4b9d74d3883aa4fd1eaf.1712813475.git.jpoimboe@kernel.org>
Date: Wed, 10 Apr 2024 22:40:46 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexandre Chartre <alexandre.chartre@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	KP Singh <kpsingh@...nel.org>,
	Waiman Long <longman@...hat.com>,
	Borislav Petkov <bp@...en8.de>
Subject: [PATCH 2/7] x86/bugs: Cache the value of MSR_IA32_ARCH_CAPABILITIES

There's no need to keep reading MSR_IA32_ARCH_CAPABILITIES over and
over.  It's even read in the BHI sysfs function which is a big no-no.
Just read it once and cache it.

Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/kernel/cpu/bugs.c | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 295463707e68..27d6d64eeec3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -61,6 +61,8 @@ EXPORT_PER_CPU_SYMBOL_GPL(x86_spec_ctrl_current);
 u64 x86_pred_cmd __ro_after_init = PRED_CMD_IBPB;
 EXPORT_SYMBOL_GPL(x86_pred_cmd);
 
+static u64 __ro_after_init ia32_cap;
+
 static DEFINE_MUTEX(spec_ctrl_mutex);
 
 void (*x86_return_thunk)(void) __ro_after_init = __x86_return_thunk;
@@ -144,6 +146,8 @@ void __init cpu_select_mitigations(void)
 		x86_spec_ctrl_base &= ~SPEC_CTRL_MITIGATIONS_MASK;
 	}
 
+	ia32_cap = x86_read_arch_cap_msr();
+
 	/* Select the proper CPU mitigations before patching alternatives: */
 	spectre_v1_select_mitigation();
 	spectre_v2_select_mitigation();
@@ -301,8 +305,6 @@ static const char * const taa_strings[] = {
 
 static void __init taa_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_TAA)) {
 		taa_mitigation = TAA_MITIGATION_OFF;
 		return;
@@ -341,7 +343,6 @@ static void __init taa_select_mitigation(void)
 	 * On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode
 	 * update is required.
 	 */
-	ia32_cap = x86_read_arch_cap_msr();
 	if ( (ia32_cap & ARCH_CAP_MDS_NO) &&
 	    !(ia32_cap & ARCH_CAP_TSX_CTRL_MSR))
 		taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
@@ -401,8 +402,6 @@ static const char * const mmio_strings[] = {
 
 static void __init mmio_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
 	     boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
 	     cpu_mitigations_off()) {
@@ -413,8 +412,6 @@ static void __init mmio_select_mitigation(void)
 	if (mmio_mitigation == MMIO_MITIGATION_OFF)
 		return;
 
-	ia32_cap = x86_read_arch_cap_msr();
-
 	/*
 	 * Enable CPU buffer clear mitigation for host and VMM, if also affected
 	 * by MDS or TAA. Otherwise, enable mitigation for VMM only.
@@ -508,7 +505,7 @@ static void __init rfds_select_mitigation(void)
 	if (rfds_mitigation == RFDS_MITIGATION_OFF)
 		return;
 
-	if (x86_read_arch_cap_msr() & ARCH_CAP_RFDS_CLEAR)
+	if (ia32_cap & ARCH_CAP_RFDS_CLEAR)
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
 	else
 		rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
@@ -659,8 +656,6 @@ void update_srbds_msr(void)
 
 static void __init srbds_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_SRBDS))
 		return;
 
@@ -669,7 +664,6 @@ static void __init srbds_select_mitigation(void)
 	 * are only exposed to SRBDS when TSX is enabled or when CPU is affected
 	 * by Processor MMIO Stale Data vulnerability.
 	 */
-	ia32_cap = x86_read_arch_cap_msr();
 	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) &&
 	    !boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
 		srbds_mitigation = SRBDS_MITIGATION_TSX_OFF;
@@ -813,7 +807,7 @@ static void __init gds_select_mitigation(void)
 	/* Will verify below that mitigation _can_ be disabled */
 
 	/* No microcode */
-	if (!(x86_read_arch_cap_msr() & ARCH_CAP_GDS_CTRL)) {
+	if (!(ia32_cap & ARCH_CAP_GDS_CTRL)) {
 		if (gds_mitigation == GDS_MITIGATION_FORCE) {
 			/*
 			 * This only needs to be done on the boot CPU so do it
@@ -1908,8 +1902,6 @@ static void update_indir_branch_cond(void)
 /* Update the static key controlling the MDS CPU buffer clear in idle */
 static void update_mds_branch_idle(void)
 {
-	u64 ia32_cap = x86_read_arch_cap_msr();
-
 	/*
 	 * Enable the idle clearing if SMT is active on CPUs which are
 	 * affected only by MSBDS and not any other MDS variant.
@@ -2818,7 +2810,7 @@ static const char * const spectre_bhi_state(void)
 	else if  (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP))
 		return "; BHI: SW loop, KVM: SW loop";
 	else if (boot_cpu_has(X86_FEATURE_RETPOLINE) &&
-		 !(x86_read_arch_cap_msr() & ARCH_CAP_RRSBA))
+		 !(ia32_cap & ARCH_CAP_RRSBA))
 		return "; BHI: Retpoline";
 	else if  (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
 		return "; BHI: Syscall hardening, KVM: SW loop";
-- 
2.44.0