[PATCH 6.1 59/69] x86/bugs: Cache the value of MSR_IA32_ARCH_CAPABILITIES

Greg Kroah-Hartman
2024-04-15T14:41:17Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit cb2db5bb04d7f778fbc1a1ea2507aab436f1bff3 upstream.

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@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/9592a18a814368e75f8f4b9d74d3883aa4fd1eaf.1712813475.git.jpoimboe@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/cpu/bugs.c | 22 +++++++---------------
1 file changed, 7 insertions(+), 15 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -60,6 +60,8 @@ EXPORT_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;
@@ -143,6 +145,8 @@ 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();
@@ -300,8 +304,6 @@ 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;
@@ -340,7 +342,6 @@ static void __init taa_select_mitigation
* 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;
@@ -400,8 +401,6 @@ 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()) {
@@ -412,8 +411,6 @@ static void __init mmio_select_mitigatio
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.
@@ -507,7 +504,7 @@ static void __init rfds_select_mitigatio
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;
@@ -658,8 +655,6 @@ void update_srbds_msr(void)

static void __init srbds_select_mitigation(void)
{
- u64 ia32_cap;
-
if (!boot_cpu_has_bug(X86_BUG_SRBDS))
return;

@@ -668,7 +663,6 @@ static void __init srbds_select_mitigati
* 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;
@@ -812,7 +806,7 @@ static void __init gds_select_mitigation
/* 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
@@ -1884,8 +1878,6 @@ static void update_indir_branch_cond(voi
/* 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.
@@ -2797,7 +2789,7 @@ static const char *spectre_bhi_state(voi
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";