x86/tsx: Add a feature bit for TSX control MSR support

commit aaa65d17eec372c6a9756833f3964ba05b05ea14 upstream.

Support for the TSX control MSR is enumerated in MSR_IA32_ARCH_CAPABILITIES.
This is different from how other CPU features are enumerated i.e. via
CPUID. Currently, a call to tsx_ctrl_is_supported() is required for
enumerating the feature. In the absence of a feature bit for TSX control,
any code that relies on checking feature bits directly will not work.

In preparation for adding a feature bit check in MSR save/restore
during suspend/resume, set a new feature bit X86_FEATURE_TSX_CTRL when
MSR_IA32_TSX_CTRL is present.

  [ bp: Remove tsx_ctrl_is_supported()]

  [Pawan: Resolved conflicts in backport; Removed parts of commit message
          referring to removed function tsx_ctrl_is_supported()]

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/de619764e1d98afbb7a5fa58424f1278ede37b45.1668539735.git.pawan.kumar.gupta@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 15 insertions, 19 deletions

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index a033fa5c596d..429e6fc5069f 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -196,6 +196,7 @@
 #define X86_FEATURE_FENCE_SWAPGS_KERNEL	( 7*32+11) /* "" LFENCE in kernel entry SWAPGS path */
 #define X86_FEATURE_RETPOLINE	( 7*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_RETPOLINE_LFENCE	( 7*32+13) /* "" Use LFENCE for Spectre variant 2 */
+#define X86_FEATURE_MSR_TSX_CTRL	( 7*32+14) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
 
 #define X86_FEATURE_MSR_SPEC_CTRL ( 7*32+16) /* "" MSR SPEC_CTRL is implemented */
 #define X86_FEATURE_SSBD	( 7*32+17) /* Speculative Store Bypass Disable */
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
index 032509adf9de..88a553ee7704 100644
--- a/arch/x86/kernel/cpu/tsx.c
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -55,24 +55,6 @@ void tsx_enable(void)
 	wrmsrl(MSR_IA32_TSX_CTRL, tsx);
 }
 
-static bool __init tsx_ctrl_is_supported(void)
-{
-	u64 ia32_cap = x86_read_arch_cap_msr();
-
-	/*
-	 * TSX is controlled via MSR_IA32_TSX_CTRL.  However, support for this
-	 * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES.
-	 *
-	 * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a
-	 * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES
-	 * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get
-	 * MSR_IA32_TSX_CTRL support even after a microcode update. Thus,
-	 * tsx= cmdline requests will do nothing on CPUs without
-	 * MSR_IA32_TSX_CTRL support.
-	 */
-	return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
-}
-
 static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
 {
 	if (boot_cpu_has_bug(X86_BUG_TAA))
@@ -86,9 +68,22 @@ void __init tsx_init(void)
 	char arg[5] = {};
 	int ret;
 
-	if (!tsx_ctrl_is_supported())
+	/*
+	 * TSX is controlled via MSR_IA32_TSX_CTRL.  However, support for this
+	 * MSR is enumerated by ARCH_CAP_TSX_MSR bit in MSR_IA32_ARCH_CAPABILITIES.
+	 *
+	 * TSX control (aka MSR_IA32_TSX_CTRL) is only available after a
+	 * microcode update on CPUs that have their MSR_IA32_ARCH_CAPABILITIES
+	 * bit MDS_NO=1. CPUs with MDS_NO=0 are not planned to get
+	 * MSR_IA32_TSX_CTRL support even after a microcode update. Thus,
+	 * tsx= cmdline requests will do nothing on CPUs without
+	 * MSR_IA32_TSX_CTRL support.
+	 */
+	if (!(x86_read_arch_cap_msr() & ARCH_CAP_TSX_CTRL_MSR))
 		return;
 
+	setup_force_cpu_cap(X86_FEATURE_MSR_TSX_CTRL);
+
 	ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg));
 	if (ret >= 0) {
 		if (!strcmp(arg, "on")) {