[Xen-devel] [PATCH] xen: debug_registers_trap, perf_counters_trap, and "static_partitioning"

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Introduce two global parameters to disable debug registers trapping and
perf counters trapping. They are only safe to use in static partitiong
scenarios where sched=null is used -- vcpu cannot be migrated from one
pcpu to the next.

Introduce a new simple umbrella command line option
"static_partitioning" that enables vwfi=native, sched=null, and also
sets debug_registers_trap and perf_counters_trap to false.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
CC: Dario Faggioli <dfaggioli@xxxxxxxx>
---
This is not ideal. The best course of action would be to implement
proper context switching of all the necessary debug and perf counters
registers. This is an imperfect shortcut, which could reasonably be left
out of the upstream tree but I shared it with others for their
convenience.
---
 xen/arch/arm/traps.c    | 26 +++++++++++++++++++++++++-
 xen/common/schedule.c   |  2 +-
 xen/include/xen/sched.h |  1 +
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 5c18e918b0..d6eaffde23 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -118,6 +118,28 @@ static int __init parse_vwfi(const char *s)
 }
 custom_param("vwfi", parse_vwfi);
 
+static bool debug_registers_trap = true;
+static bool perf_counters_trap = true;
+
+static int __init opt_static_partitioning(const char *s)
+{
+    if ( strcmp(s, "true") && 
+         strcmp(s, "True") &&
+         strcmp(s, "1") )
+        return 0;
+
+    vwfi = NATIVE;
+    debug_registers_trap = false;
+    perf_counters_trap = false;
+    memcpy(opt_sched, "null", 5);
+
+    /* Disable Trap Debug and Performance Monitor now for CPU0 */
+    WRITE_SYSREG(HDCR_TDRA, MDCR_EL2);
+
+    return 0;
+}
+custom_param("static_partitioning", opt_static_partitioning);
+
 register_t get_default_hcr_flags(void)
 {
     return  (HCR_PTW|HCR_BSU_INNER|HCR_AMO|HCR_IMO|HCR_FMO|HCR_VM|
@@ -165,7 +187,9 @@ void init_traps(void)
     WRITE_SYSREG((vaddr_t)hyp_traps_vector, VBAR_EL2);
 
     /* Trap Debug and Performance Monitor accesses */
-    WRITE_SYSREG(HDCR_TDRA|HDCR_TDOSA|HDCR_TDA|HDCR_TPM|HDCR_TPMCR,
+    WRITE_SYSREG(HDCR_TDRA |
+                 (debug_registers_trap ? HDCR_TDOSA|HDCR_TDA : 0) |
+                 (perf_counters_trap ? HDCR_TPM|HDCR_TPMCR : 0),
                  MDCR_EL2);
 
     /* Trap CP15 c15 used for implementation defined registers */
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 049f93f7aa..51eb3d770b 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -39,7 +39,7 @@
 #include <xen/err.h>
 
 /* opt_sched: scheduler - default to configured value */
-static char __initdata opt_sched[10] = CONFIG_SCHED_DEFAULT;
+char __initdata opt_sched[10] = CONFIG_SCHED_DEFAULT;
 string_param("sched", opt_sched);
 
 /* if sched_smt_power_savings is set,
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index b73ccbdf3a..c40a1b5dbc 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -906,6 +906,7 @@ static inline bool is_vcpu_online(const struct vcpu *v)
 }
 
 extern bool sched_smt_power_savings;
+extern char opt_sched[10];
 
 extern enum cpufreq_controller {
     FREQCTL_none, FREQCTL_dom0_kernel, FREQCTL_xen
-- 
2.17.1


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