[PATCH v2 0/2] Check enumeration before MSR save/restore

[PATCH v2 0/2] Check enumeration before MSR save/restore

[Pawan Gupta]

v2:
- Dropped patch for X86_FEATURE_AMD64_LS_CFG, using X86_FEATURE_AMD64_LS_CFG_SSBD instead.
- Commit message updated.

v1: https://lore.kernel.org/lkml/cover.1663025154.git.pawan.kumar.gupta@linux.intel.com/

Hi,

This patchset is to fix the "unchecked MSR access error" [1] during S3
resume. Patch 1/3 adds a feature bit for MSR_IA32_TSX_CTRL.

Patch 2/3 adds a feature bit for MSR_AMD64_LS_CFG.

Patch 3/3 adds check for feature bit before adding any speculation
control MSR to the list of MSRs to save/restore.

[1] https://lore.kernel.org/lkml/20220906201743.436091-1-hdegoede@redhat.com/

Thanks,
Pawan

Pawan Gupta (2):
  x86/tsx: Add feature bit for TSX control MSR support
  x86/pm: Add enumeration check before spec MSRs save/restore setup

 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/kernel/cpu/tsx.c          | 30 +++++++++++++++---------------
 arch/x86/power/cpu.c               | 23 ++++++++++++++++-------
 3 files changed, 32 insertions(+), 22 deletions(-)

-- 
2.37.3

[PATCH v2 1/2] x86/tsx: Add feature bit for TSX control MSR support

[Pawan Gupta]

Support for 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 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. Also make tsx_ctrl_is_supported() use the
new feature bit to avoid any overhead of reading the MSR.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/kernel/cpu/tsx.c          | 30 +++++++++++++++---------------
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index b71f4f2ecdd5..3cda06ebe046 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -304,6 +304,7 @@
 #define X86_FEATURE_UNRET		(11*32+15) /* "" AMD BTB untrain return */
 #define X86_FEATURE_USE_IBPB_FW		(11*32+16) /* "" Use IBPB during runtime firmware calls */
 #define X86_FEATURE_RSB_VMEXIT_LITE	(11*32+17) /* "" Fill RSB on VM exit when EIBRS is enabled */
+#define X86_FEATURE_MSR_TSX_CTRL	(11*32+18) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
index ec7bbac3a9f2..9fe488dbed15 100644
--- a/arch/x86/kernel/cpu/tsx.c
+++ b/arch/x86/kernel/cpu/tsx.c
@@ -60,20 +60,7 @@ static void tsx_enable(void)
 
 static bool 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);
+	return cpu_feature_enabled(X86_FEATURE_MSR_TSX_CTRL);
 }
 
 static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
@@ -191,7 +178,20 @@ void __init tsx_init(void)
 		return;
 	}
 
-	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) {
+		setup_force_cpu_cap(X86_FEATURE_MSR_TSX_CTRL);
+	} else {
 		tsx_ctrl_state = TSX_CTRL_NOT_SUPPORTED;
 		return;
 	}
-- 
2.37.3

[PATCH v2 2/2] x86/pm: Add enumeration check before spec MSRs save/restore setup

[Pawan Gupta]

pm_save_spec_msr() keeps a list of all the MSRs which _might_ need to be
saved and restored at hibernate?? and resume??.  However, it has zero
awareness of CPU support for these MSRs.  It mostly works by
unconditionally attempting to manipulate these MSRs and relying on
rdmsrl_safe() being able to handle a #GP on CPUs where the support is
unavailable.

However, it's possible for reads (RDMSR) to be supported for a given MSR
while writes (WRMSR) are not.  In this case, msr_build_context() sees a
successful read (RDMSR) and marks the MSR as 'valid'.  Then, later, a
write (WRMSR) fails, producing a nasty (but harmless) error message.
This causes restore_processor_state() to try and restore it, but writing
this MSR is not allowed on the Intel Atom N2600 leading to:

  unchecked MSR access error: WRMSR to 0x122 (tried to write 0x0000000000000002) \
     at rIP: 0xffffffff8b07a574 (native_write_msr+0x4/0x20)
  Call Trace:
   <TASK>
   restore_processor_state
   x86_acpi_suspend_lowlevel
   acpi_suspend_enter
   suspend_devices_and_enter
   pm_suspend.cold
   state_store
   kernfs_fop_write_iter
   vfs_write
   ksys_write
   do_syscall_64
   ? do_syscall_64
   ? up_read
   ? lock_is_held_type
   ? asm_exc_page_fault
   ? lockdep_hardirqs_on
   entry_SYSCALL_64_after_hwframe

To fix this, add the corresponding X86_FEATURE bit for each MSR.  Avoid
trying to manipulate the MSR when the feature bit is clear. This
required adding a X86_FEATURE bit for MSRs that do not have one already,
but it's a small price to pay.

Fixes: 73924ec4d560 ("x86/pm: Save the MSR validity status at context setup")
Reported-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 arch/x86/power/cpu.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index bb176c72891c..0d97c25551f0 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -511,17 +511,26 @@ static int pm_cpu_check(const struct x86_cpu_id *c)
 	return ret;
 }
 
+struct msr_enumeration {
+	u32 msr_no;
+	u32 feature;
+};
+
 static void pm_save_spec_msr(void)
 {
-	u32 spec_msr_id[] = {
-		MSR_IA32_SPEC_CTRL,
-		MSR_IA32_TSX_CTRL,
-		MSR_TSX_FORCE_ABORT,
-		MSR_IA32_MCU_OPT_CTRL,
-		MSR_AMD64_LS_CFG,
+	struct msr_enumeration msr_enum[] = {
+		{MSR_IA32_SPEC_CTRL,	X86_FEATURE_MSR_SPEC_CTRL},
+		{MSR_IA32_TSX_CTRL,	X86_FEATURE_MSR_TSX_CTRL},
+		{MSR_TSX_FORCE_ABORT,	X86_FEATURE_TSX_FORCE_ABORT},
+		{MSR_IA32_MCU_OPT_CTRL,	X86_FEATURE_SRBDS_CTRL},
+		{MSR_AMD64_LS_CFG,	X86_FEATURE_LS_CFG_SSBD},
 	};
+	int i;
 
-	msr_build_context(spec_msr_id, ARRAY_SIZE(spec_msr_id));
+	for (i = 0; i < ARRAY_SIZE(msr_enum); i++) {
+		if (boot_cpu_has(msr_enum[i].feature))
+			msr_build_context(&msr_enum[i].msr_no, 1);
+	}
 }
 
 static int pm_check_save_msr(void)
-- 
2.37.3