[PATCH 1/2] powerpc/perf: Add mtmmcr0(FC) after ppc_set_pmu_inuse(1)

[PATCH 1/2] powerpc/perf: Add mtmmcr0(FC) after ppc_set_pmu_inuse(1)

[Madhavan Srinivasan]

pmu_inuse flag is part of lppaca struct which notifies the hypervisor
whether guest/partition is using PMUs. This provides a hint incase of
save/restore of PMU registers. And in power_pmu_enable(), linux sets
the pmu_inuse flag and then updates the PMU registers. Current sequence
in power_pmu_enable() is 1) update pmc_inuse flag 2)update MMCRA, MMCR1,
MMCR0 and so on. But with this sequence, there is a window where when
updating MMCRA, hypersior could load stale value to MMCR0 which could
cause a PMI exception. Patch add a mtmmcr0 with freeze counter bit set
right after updating the pmu_inuse flag to avoid any overflow scenarios.
---
 arch/powerpc/perf/core-book3s.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 3fb6d265ed17..f455e274281a 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1351,6 +1351,7 @@ static void power_pmu_enable(struct pmu *pmu)
 	 * Then unfreeze the events.
 	 */
 	ppc_set_pmu_inuse(1);
+	mtspr(SPRN_MMCR0, MMCR0_FC);
 	mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
 	mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
 	mtspr(SPRN_MMCR0, (cpuhw->mmcr[0] & ~(MMCR0_PMC1CE | MMCR0_PMCjCE))
-- 
2.21.0

[PATCH 2/2] powerpc/perf: Check pmus_inuse flag in perf_event_print_debug()

[Madhavan Srinivasan]

pmu_inuse flag is part of lppaca struct which notifies the hypervisor
whether guest/partition is using PMUs. This provides a hint for
save/restore of PMU registers. Currently perf_event_print_debug()
does not check for pmu_inuse flag and it is not safe to use it to
dump PMU SPRs in a CONFIG_PSERIES.

Patch adds two things here. 1) An inline ppc_get_pmu_inuse() to get
the pmu_inuse value and 2)check in perf_event_print_debug() before
dumping the PMU SPRs.

ppc_get_pmu_inuse() is based on ppc_set_pmu_inuse() and includes same
CONFIG_ checks.
---
 arch/powerpc/include/asm/pmc.h  | 15 +++++++++++++++
 arch/powerpc/perf/core-book3s.c |  9 +++++++++
 2 files changed, 24 insertions(+)

diff --git a/arch/powerpc/include/asm/pmc.h b/arch/powerpc/include/asm/pmc.h
index c6bbe9778d3c..35179d218e2e 100644
--- a/arch/powerpc/include/asm/pmc.h
+++ b/arch/powerpc/include/asm/pmc.h
@@ -34,11 +34,26 @@ static inline void ppc_set_pmu_inuse(int inuse)
 #endif
 }
 
+static inline u8 ppc_get_pmu_inuse(void)
+{
+#if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_BOOK3S_HV_POSSIBLE)
+	if (firmware_has_feature(FW_FEATURE_LPAR)) {
+#ifdef CONFIG_PPC_PSERIES
+		return get_lppaca()->pmcregs_in_use;
+#endif
+	}
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+	return get_paca()->pmcregs_in_use;
+#endif
+#endif
+}
+
 extern void power4_enable_pmcs(void);
 
 #else /* CONFIG_PPC64 */
 
 static inline void ppc_set_pmu_inuse(int inuse) { }
+static inline u8 ppc_get_pmu_inuse(void) { }
 
 #endif
 
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index f455e274281a..855a5f9589ef 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -816,6 +816,15 @@ void perf_event_print_debug(void)
 	if (!ppmu->n_counter)
 		return;
 
+	/*
+	 * Check pmu_inuse flag. As per PAPR spec, hypersivor
+	 * will save/restore the PMU regs only if pmu_inuse is
+	 * set. If its not enable, values dumped from these SPRs
+	 * may not be valid or useful.
+	 */
+	if (!ppc_get_pmu_inuse())
+		return;
+
 	local_irq_save(flags);
 
 	pr_info("CPU: %d PMU registers, ppmu = %s n_counters = %d",
-- 
2.21.0

Re: [PATCH 2/2] powerpc/perf: Check pmus_inuse flag in perf_event_print_debug()

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1748 bytes --]

Hi Madhavan,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on powerpc/next]
[also build test WARNING on v5.4-rc7 next-20191111]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Madhavan-Srinivasan/powerpc-perf-Add-mtmmcr0-FC-after-ppc_set_pmu_inuse-1/20191109-143451
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
config: powerpc-pmac32_defconfig (attached as .config)
compiler: powerpc-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=powerpc 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from arch/powerpc/oprofile/common.c:17:0:
   arch/powerpc/include/asm/pmc.h: In function 'ppc_get_pmu_inuse':
>> arch/powerpc/include/asm/pmc.h:56:1: warning: no return statement in function returning non-void [-Wreturn-type]
    static inline u8 ppc_get_pmu_inuse(void) { }
    ^~~~~~

vim +56 arch/powerpc/include/asm/pmc.h

    54	
    55	static inline void ppc_set_pmu_inuse(int inuse) { }
  > 56	static inline u8 ppc_get_pmu_inuse(void) { }
    57	

---
0-DAY kernel test infrastructure                 Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 24436 bytes --]