[PATCH -fixes] drivers: perf: Fix panic in riscv SBI mmap support

Alexandre Ghiti
2023-10-06T08:20:45Z

The following panic can happen when mmap is called before the pmu add
callback which sets the hardware counter index: this happens for example
with the following command `perf record --no-bpf-event -n kill`.

[ 99.461486] CPU: 1 PID: 1259 Comm: perf Tainted: G E 6.6.0-rc4ubuntu-defconfig #2
[ 99.461669] Hardware name: riscv-virtio,qemu (DT)
[ 99.461748] epc : pmu_sbi_set_scounteren+0x42/0x44
[ 99.462337] ra : smp_call_function_many_cond+0x126/0x5b0
[ 99.462369] epc : ffffffff809f9d24 ra : ffffffff800f93e0 sp : ff60000082153aa0
[ 99.462407] gp : ffffffff82395c98 tp : ff6000009a218040 t0 : ff6000009ab3a4f0
[ 99.462425] t1 : 0000000000000004 t2 : 0000000000000100 s0 : ff60000082153ab0
[ 99.462459] s1 : 0000000000000000 a0 : ff60000098869528 a1 : 0000000000000000
[ 99.462473] a2 : 000000000000001f a3 : 0000000000f00000 a4 : fffffffffffffff8
[ 99.462488] a5 : 00000000000000cc a6 : 0000000000000000 a7 : 0000000000735049
[ 99.462502] s2 : 0000000000000001 s3 : ffffffff809f9ce2 s4 : ff60000098869528
[ 99.462516] s5 : 0000000000000002 s6 : 0000000000000004 s7 : 0000000000000001
[ 99.462530] s8 : ff600003fec98bc0 s9 : ffffffff826c5890 s10: ff600003fecfcde0
[ 99.462544] s11: ff600003fec98bc0 t3 : ffffffff819e2558 t4 : ff1c000004623840
[ 99.462557] t5 : 0000000000000901 t6 : ff6000008feeb890
[ 99.462570] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
[ 99.462658] [<ffffffff809f9d24>] pmu_sbi_set_scounteren+0x42/0x44
[ 99.462979] Code: 1060 4785 97bb 00d7 8fd9 9073 1067 6422 0141 8082 (9002) 0013
[ 99.463335] Kernel BUG [#2]

To circumvent this, try to enable userspace access to the hardware counter
when it is selected in addition to when the event is mapped. And vice-versa
when the event is stopped/unmapped.

Fixes: cc4c07c89aad ("drivers: perf: Implement perf event mmap support in the SBI backend")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
drivers/perf/riscv_pmu.c | 3 ++-
drivers/perf/riscv_pmu_sbi.c | 16 ++++++++++------
2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index 1f9a35f724f5..0dda70e1ef90 100644
--- a/drivers/perf/riscv_pmu.c
+++ b/drivers/perf/riscv_pmu.c
@@ -23,7 +23,8 @@ static bool riscv_perf_user_access(struct perf_event *event)
return ((event->attr.type == PERF_TYPE_HARDWARE) ||
(event->attr.type == PERF_TYPE_HW_CACHE) ||
(event->attr.type == PERF_TYPE_RAW)) &&
- !!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
+ !!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT) &&
+ (event->hw.idx != -1);
}

void arch_perf_update_userpage(struct perf_event *event,
diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 9a51053b1f99..96c7f670c8f0 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -510,16 +510,18 @@ static void pmu_sbi_set_scounteren(void *arg)
{
struct perf_event *event = (struct perf_event *)arg;

- csr_write(CSR_SCOUNTEREN,
- csr_read(CSR_SCOUNTEREN) | (1 << pmu_sbi_csr_index(event)));
+ if (event->hw.idx != -1)
+ csr_write(CSR_SCOUNTEREN,
+ csr_read(CSR_SCOUNTEREN) | (1 << pmu_sbi_csr_index(event)));
}

static void pmu_sbi_reset_scounteren(void *arg)
{
struct perf_event *event = (struct perf_event *)arg;

- csr_write(CSR_SCOUNTEREN,
- csr_read(CSR_SCOUNTEREN) & ~(1 << pmu_sbi_csr_index(event)));
+ if (event->hw.idx != -1)
+ csr_write(CSR_SCOUNTEREN,
+ csr_read(CSR_SCOUNTEREN) & ~(1 << pmu_sbi_csr_index(event)));
}

static void pmu_sbi_ctr_start(struct perf_event *event, u64 ival)
@@ -541,7 +543,8 @@ static void pmu_sbi_ctr_start(struct perf_event *event, u64 ival)

if ((hwc->flags & PERF_EVENT_FLAG_USER_ACCESS) &&
(hwc->flags & PERF_EVENT_FLAG_USER_READ_CNT))
- pmu_sbi_set_scounteren((void *)event);
+ on_each_cpu_mask(mm_cpumask(event->owner->mm),
+ pmu_sbi_set_scounteren, (void *)event, 1);
}

static void pmu_sbi_ctr_stop(struct perf_event *event, unsigned long flag)
@@ -551,7 +554,8 @@ static void pmu_sbi_ctr_stop(struct perf_event *event, unsigned long flag)

if ((hwc->flags & PERF_EVENT_FLAG_USER_ACCESS) &&
(hwc->flags & PERF_EVENT_FLAG_USER_READ_CNT))
- pmu_sbi_reset_scounteren((void *)event);
+ on_each_cpu_mask(mm_cpumask(event->owner->mm),
+ pmu_sbi_reset_scounteren, (void *)event, 1);

ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, hwc->idx, 1, flag, 0, 0, 0);
if (ret.error && (ret.error != SBI_ERR_ALREADY_STOPPED) &&
--
2.39.2

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