On 09/09/2020 17:05, Suzuki K Poulose wrote:

On 09/09/2020 08:56 AM, Jonathan Zhou wrote:

quoted

Hi Suzuki

Thanks for your review.

On 08/09/2020 17:56, Suzuki K Poulose wrote:

quoted

On 08/31/2020 09:02 AM, Jonathan Zhou wrote:

quoted

ARMv8.4 architecture extension introduces ARMv8.4-Trace, Armv8.4
Self-hosted Trace Extensions. It provides control of exception
levels and security states. Let's add this feature detection and
enable E1TRE and E0TRE in TRFCR_EL1 if Self-hosted Trace is
supported.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Shaokun Zhang <redacted>
Signed-off-by: Jonathan Zhou <redacted>
---
   arch/arm64/include/asm/sysreg.h               |  8 ++++++++
   drivers/hwtracing/coresight/coresight-etm4x.c | 23
+++++++++++++++++++++++
   2 files changed, 31 insertions(+)

diff --git a/arch/arm64/include/asm/sysreg.h

b/arch/arm64/include/asm/sysreg.h
index 554a7e8ecb07..53da5f326667 100644

--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h

@@ -184,6 +184,13 @@

     #define SYS_ZCR_EL1            sys_reg(3, 0, 1, 2, 0)
   +/* Trace Filter control */
+#define SYS_TRFCR_EL1            sys_reg(3, 0, 1, 2, 1)

quoted

+/* Trace is allowed at EL0 */
+#define SYS_TRFCR_EL1_E0TRE        BIT(0)
+/* Trace is allowed at EL1 */
+#define SYS_TRFCR_EL1_E1TRE        BIT(1)
+

Please drop SYS suffix for the fields.

Thanks, I will fix this.

quoted

quoted

   #define SYS_TTBR0_EL1            sys_reg(3, 0, 2, 0, 0)
   #define SYS_TTBR1_EL1            sys_reg(3, 0, 2, 0, 1)
   #define SYS_TCR_EL1            sys_reg(3, 0, 2, 0, 2)

@@ -772,6 +779,7 @@

   #define ID_AA64MMFR2_CNP_SHIFT        0
     /* id_aa64dfr0 */
+#define ID_AA64DFR0_SELF_HOSTED_SHIFT    40
   #define ID_AA64DFR0_DOUBLELOCK_SHIFT    36
   #define ID_AA64DFR0_PMSVER_SHIFT    32
   #define ID_AA64DFR0_CTX_CMPS_SHIFT    28

diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c

b/drivers/hwtracing/coresight/coresight-etm4x.c
index 96425e818fc2..f72b457c2bad 100644

--- a/drivers/hwtracing/coresight/coresight-etm4x.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x.c

@@ -28,6 +28,7 @@

   #include <linux/perf_event.h>
   #include <linux/pm_runtime.h>
   #include <linux/property.h>
+#include <asm/sysreg.h>
   #include <asm/sections.h>
   #include <asm/local.h>
   #include <asm/virt.h>

@@ -785,6 +786,24 @@ static void etm4_init_arch_data(void *info)

       CS_LOCK(drvdata->base);
   }
   +static void etm4_init_sysctrl(void *info)
+{
+    u64 sys_trfcr_el1, dfr0;
+    int trace_filt;
+
+    dfr0 = read_sysreg(id_aa64dfr0_el1);
+
+    trace_filt = cpuid_feature_extract_unsigned_field(dfr0,
+                    ID_AA64DFR0_SELF_HOSTED_SHIFT);
+    /* if selfhosted trace implemented, enable trace EL0 as
default. */

What about EL1 ? We do support kernel tracing. I believe we need to do
this every time when we enable etm4, based on the selected config.

I don't know if it's possible to run trace sessions in a guest OS, so I
left the EL1 and EL2 trace disabled. And it's right. We need to provide
an interface to select these configs include the CX and TS feilds of
TRFCR_EL2. How about a sysfs interface?

No, you don't need any additional interfaces. The etm4_config should
tell us, if the ETM4 is supposed to filter events for kernel/userspace.
We don't have virtualization support yet, so we could ignore the
TRFCR_EL2, for now.

Thanks, virtualization is really something out of my mind.

Either we :

1) Unconditionally enable EL1 & EL0 tracing on each ETMv4 instance
at probe time and leave the trace exclusion by EL to deal with the
kernel/userspace filtering.

OR

2) For each session of ETMv4 tracing, program the EL1 and EL0 trace
in TRFCR_EL1 based on the exclusion requested by ELs in the configs.

I prefer (1). Also, we must enable CX for TRFCR_EL2, if we are in VHE
to allow contextid tracing.

Yes, (1) seems to be better. Programming TRFCR_ELx based on the ETM
viewinst ELs' configs looks a little strange, for they are filters on
different level. I will apply this in PATCH V3.

Regards.
Jonathan

TS could be set to 0b01 in either case, to use the virtual timestamp.

Suzuki

quoted

Regards.
Jonathan.

quoted

Suzuki
.

.

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