3 files changed, 72 insertions, 0 deletions

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 61a027b694a3..3eccc42e2d88 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3361,6 +3361,13 @@ static void intel_snb_check_microcode(void)
 	}
 }
 
+static bool is_lbr_from(unsigned long msr)
+{
+	unsigned long lbr_from_nr = x86_pmu.lbr_from + x86_pmu.lbr_nr;
+
+	return x86_pmu.lbr_from <= msr && msr < lbr_from_nr;
+}
+
 /*
  * Under certain circumstances, access certain MSR may cause #GP.
  * The function tests if the input MSR can be safely accessed.
@@ -3381,13 +3388,24 @@ static bool check_msr(unsigned long msr, u64 mask)
 	 * Only change the bits which can be updated by wrmsrl.
 	 */
 	val_tmp = val_old ^ mask;
+
+	if (is_lbr_from(msr))
+		val_tmp = lbr_from_signext_quirk_wr(val_tmp);
+
 	if (wrmsrl_safe(msr, val_tmp) ||
 	    rdmsrl_safe(msr, &val_new))
 		return false;
 
+	/*
+	 * Quirk only affects validation in wrmsr(), so wrmsrl()'s value
+	 * should equal rdmsrl()'s even with the quirk.
+	 */
 	if (val_new != val_tmp)
 		return false;
 
+	if (is_lbr_from(msr))
+		val_old = lbr_from_signext_quirk_wr(val_old);
+
 	/* Here it's sure that the MSR can be safely accessed.
 	 * Restore the old value and return.
 	 */
diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 2dca66cec617..88093e0915a9 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -81,6 +81,8 @@ static enum {
 #define LBR_FROM_FLAG_IN_TX    (1ULL << 62)
 #define LBR_FROM_FLAG_ABORT    (1ULL << 61)
 
+#define LBR_FROM_SIGNEXT_2MSB	(BIT_ULL(60) | BIT_ULL(59))
+
 /*
  * x86control flow change classification
  * x86control flow changes include branches, interrupts, traps, faults
@@ -235,6 +237,53 @@ enum {
 	LBR_VALID,
 };
 
+/*
+ * For formats with LBR_TSX flags (e.g. LBR_FORMAT_EIP_FLAGS2), bits 61:62 in
+ * MSR_LAST_BRANCH_FROM_x are the TSX flags when TSX is supported, but when
+ * TSX is not supported they have no consistent behavior:
+ *
+ *   - For wrmsr(), bits 61:62 are considered part of the sign extension.
+ *   - For HW updates (branch captures) bits 61:62 are always OFF and are not
+ *     part of the sign extension.
+ *
+ * Therefore, if:
+ *
+ *   1) LBR has TSX format
+ *   2) CPU has no TSX support enabled
+ *
+ * ... then any value passed to wrmsr() must be sign extended to 63 bits and any
+ * value from rdmsr() must be converted to have a 61 bits sign extension,
+ * ignoring the TSX flags.
+ */
+static inline bool lbr_from_signext_quirk_needed(void)
+{
+	int lbr_format = x86_pmu.intel_cap.lbr_format;
+	bool tsx_support = boot_cpu_has(X86_FEATURE_HLE) ||
+			   boot_cpu_has(X86_FEATURE_RTM);
+
+	return !tsx_support && (lbr_desc[lbr_format] & LBR_TSX);
+}
+
+DEFINE_STATIC_KEY_FALSE(lbr_from_quirk_key);
+
+/* If quirk is enabled, ensure sign extension is 63 bits: */
+inline u64 lbr_from_signext_quirk_wr(u64 val)
+{
+	if (static_branch_unlikely(&lbr_from_quirk_key)) {
+		/*
+		 * Sign extend into bits 61:62 while preserving bit 63.
+		 *
+		 * Quirk is enabled when TSX is disabled. Therefore TSX bits
+		 * in val are always OFF and must be changed to be sign
+		 * extension bits. Since bits 59:60 are guaranteed to be
+		 * part of the sign extension bits, we can just copy them
+		 * to 61:62.
+		 */
+		val |= (LBR_FROM_SIGNEXT_2MSB & val) << 2;
+	}
+	return val;
+}
+
 static void __intel_pmu_lbr_restore(struct x86_perf_task_context *task_ctx)
 {
 	int i;
@@ -1007,6 +1056,9 @@ void intel_pmu_lbr_init_hsw(void)
 
 	x86_pmu.lbr_sel_mask = LBR_SEL_MASK;
 	x86_pmu.lbr_sel_map  = hsw_lbr_sel_map;
+
+	if (lbr_from_signext_quirk_needed())
+		static_branch_enable(&lbr_from_quirk_key);
 }
 
 /* skylake */
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index e2d7285a2dac..8c4a47706296 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -902,6 +902,8 @@ void intel_ds_init(void);
 
 void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in);
 
+u64 lbr_from_signext_quirk_wr(u64 val);
+
 void intel_pmu_lbr_reset(void);
 
 void intel_pmu_lbr_enable(struct perf_event *event);