[PATCH 11/15] x86/bugs: Cache the value of MSR_IA32_ARCH_CAPABILITIES

[Yuxuan Luo]

From: Josh Poimboeuf <jpoimboe at kernel.org>

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 at kernel.org>
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Reviewed-by: Nikolay Borisov <nik.borisov at suse.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Sean Christopherson <seanjc at google.com>
Link: https://lore.kernel.org/r/9592a18a814368e75f8f4b9d74d3883aa4fd1eaf.1712813475.git.jpoimboe@kernel.org
(backported from commit cb2db5bb04d7f778fbc1a1ea2507aab436f1bff3)
[yuxuan.luo: The conflict around rfds_mitigations is caused by missing
 8076fcde016c (“x86/rfds: Mitigate Register File Data Sampling (RFDS)”).
 Since it’s a huge feature patch and is out of the scope of this CVE,
 ignore this conflict.
]
CVE-2024-2201
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 arch/x86/kernel/cpu/bugs.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index cd69490b65722..476ee30222578 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -54,6 +54,8 @@ EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
 DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
 EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
 
+static u64 __ro_after_init ia32_cap;
+
 static DEFINE_MUTEX(spec_ctrl_mutex);
 
 /* Update SPEC_CTRL MSR and its cached copy unconditionally */
@@ -131,6 +133,8 @@ 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();
@@ -281,8 +285,6 @@ 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;
@@ -321,7 +323,6 @@ 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;
@@ -381,8 +382,6 @@ 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()) {
@@ -393,8 +392,6 @@ 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.
@@ -563,8 +560,6 @@ void update_srbds_msr(void)
 
 static void __init srbds_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_SRBDS))
 		return;
 
@@ -573,7 +568,6 @@ 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;
@@ -689,7 +683,7 @@ 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
@@ -1652,8 +1646,6 @@ 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.
@@ -2356,7 +2348,7 @@ 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";
-- 
2.34.1