coresight: Pass guest TRFCR value to KVM

Currently the userspace and kernel filters for guests are never set, so
no trace will be generated for them. Add support for tracing guests by
passing the desired TRFCR value to KVM so it can be applied to the
guest.

By writing either E1TRE or E0TRE, filtering on either guest kernel or
guest userspace is also supported. And if both E1TRE and E0TRE are
cleared when exclude_guest is set, that option is supported too. This
change also brings exclude_host support which is difficult to add as a
separate commit without excess churn and resulting in no trace at all.

cpu_prohibit_trace() gets moved to TRBE because the ETM driver doesn't
need the read, it already has the base TRFCR value. TRBE only needs
the read to disable it and then restore.

Testing
=======

The addresses were counted with the following:

  $ perf report -D | grep -Eo 'EL2|EL1|EL0' | sort | uniq -c

Guest kernel only:

  $ perf record -e cs_etm//Gk -a -- true
    535 EL1
      1 EL2

Guest user only (only 5 addresses because the guest runs slowly in the
model):

  $ perf record -e cs_etm//Gu -a -- true
    5 EL0

Host kernel only:

  $  perf record -e cs_etm//Hk -a -- true
   3501 EL2

Host userspace only:

  $  perf record -e cs_etm//Hu -a -- true
    408 EL0
      1 EL2

Signed-off-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20250106142446.628923-8-james.clark@linaro.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -6,6 +6,7 @@
 #include <linux/acpi.h>
 #include <linux/bitops.h>
 #include <linux/kernel.h>
+#include <linux/kvm_host.h>
 #include <linux/moduleparam.h>
 #include <linux/init.h>
 #include <linux/types.h>
@@ -268,10 +269,28 @@ struct etm4_enable_arg {
  */
 static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
 {
+	u64 trfcr;
+
 	/* If the CPU doesn't support FEAT_TRF, nothing to do */
 	if (!drvdata->trfcr)
 		return;
-	cpu_prohibit_trace();
+
+	trfcr = drvdata->trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE);
+
+	write_trfcr(trfcr);
+	kvm_tracing_set_el1_configuration(trfcr);
+}
+
+static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
+{
+	u64 trfcr = drvdata->trfcr;
+
+	if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
+		trfcr &= ~TRFCR_ELx_ExTRE;
+	if (drvdata->config.mode & ETM_MODE_EXCL_USER)
+		trfcr &= ~TRFCR_ELx_E0TRE;
+
+	return trfcr;
 }
 
 /*
@@ -286,18 +305,28 @@ static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
  */
 static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
 {
-	u64 trfcr = drvdata->trfcr;
+	u64 trfcr, guest_trfcr;
 
 	/* If the CPU doesn't support FEAT_TRF, nothing to do */
-	if (!trfcr)
+	if (!drvdata->trfcr)
 		return;
 
-	if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
-		trfcr &= ~TRFCR_ELx_ExTRE;
-	if (drvdata->config.mode & ETM_MODE_EXCL_USER)
-		trfcr &= ~TRFCR_ELx_E0TRE;
+	if (drvdata->config.mode & ETM_MODE_EXCL_HOST)
+		trfcr = drvdata->trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE);
+	else
+		trfcr = etm4x_get_kern_user_filter(drvdata);
 
 	write_trfcr(trfcr);
+
+	/* Set filters for guests and pass to KVM */
+	if (drvdata->config.mode & ETM_MODE_EXCL_GUEST)
+		guest_trfcr = drvdata->trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE);
+	else
+		guest_trfcr = etm4x_get_kern_user_filter(drvdata);
+
+	/* TRFCR_EL1 doesn't have CX so mask it out. */
+	guest_trfcr &= ~TRFCR_EL2_CX;
+	kvm_tracing_set_el1_configuration(guest_trfcr);
 }
 
 #ifdef CONFIG_ETM4X_IMPDEF_FEATURE
@@ -655,6 +684,12 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
 	if (attr->exclude_user)
 		config->mode = ETM_MODE_EXCL_USER;
 
+	if (attr->exclude_host)
+		config->mode |= ETM_MODE_EXCL_HOST;
+
+	if (attr->exclude_guest)
+		config->mode |= ETM_MODE_EXCL_GUEST;
+
 	/* Always start from the default config */
 	etm4_set_default_config(config);
 

drivers/hwtracing/coresight/coresight-etm4x.h

@@ -817,7 +817,7 @@ enum etm_impdef_type {
  * @s_ex_level: Secure ELs where tracing is supported.
  */
 struct etmv4_config {
-	u32				mode;
+	u64				mode;
 	u32				pe_sel;
 	u32				cfg;
 	u32				eventctrl0;

drivers/hwtracing/coresight/coresight-priv.h

@@ -42,6 +42,9 @@ extern const struct device_type coresight_dev_type[];
 
 #define ETM_MODE_EXCL_KERN	BIT(30)
 #define ETM_MODE_EXCL_USER	BIT(31)
+#define ETM_MODE_EXCL_HOST	BIT(32)
+#define ETM_MODE_EXCL_GUEST	BIT(33)
+
 struct cs_pair_attribute {
 	struct device_attribute attr;
 	u32 lo_off;

drivers/hwtracing/coresight/coresight-self-hosted-trace.h

@@ -21,13 +21,4 @@ static inline void write_trfcr(u64 val)
 	isb();
 }
 
-static inline u64 cpu_prohibit_trace(void)
-{
-	u64 trfcr = read_trfcr();
-
-	/* Prohibit tracing at EL0 & the kernel EL */
-	write_trfcr(trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE));
-	/* Return the original value of the TRFCR */
-	return trfcr;
-}
 #endif /*  __CORESIGHT_SELF_HOSTED_TRACE_H */

drivers/hwtracing/coresight/coresight-trbe.c

@@ -1113,6 +1113,16 @@ static bool is_perf_trbe(struct perf_output_handle *handle)
 	return true;
 }
 
+static u64 cpu_prohibit_trace(void)
+{
+	u64 trfcr = read_trfcr();
+
+	/* Prohibit tracing at EL0 & the kernel EL */
+	write_trfcr(trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE));
+	/* Return the original value of the TRFCR */
+	return trfcr;
+}
+
 static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
 {
 	struct perf_output_handle **handle_ptr = dev;