From: Ravi Bangoria ravi.bangoria@amd.com

mainline inclusion from mainline-v6.1-rc6v6.1 commit baa014b9543c8e5e94f5d15b66abfe60750b8284 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9MMNG

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

--------------------------------

amd_pmu_enable_all() does:

if (!test_bit(idx, cpuc->active_mask)) continue;

amd_pmu_enable_event(cpuc->events[idx]);

A perf NMI of another event can come between these two steps. Perf NMI handler internally disables and enables _all_ events, including the one which nmi-intercepted amd_pmu_enable_all() was in process of enabling. If that unintentionally enabled event has very low sampling period and causes immediate successive NMI, causing the event to be throttled, cpuc->events[idx] and cpuc->active_mask gets cleared by x86_pmu_stop(). This will result in amd_pmu_enable_event() getting called with event=NULL when amd_pmu_enable_all() resumes after handling the NMIs. This causes a kernel crash:

BUG: kernel NULL pointer dereference, address: 0000000000000198 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page [...] Call Trace: <TASK> amd_pmu_enable_all+0x68/0xb0 ctx_resched+0xd9/0x150 event_function+0xb8/0x130 ? hrtimer_start_range_ns+0x141/0x4a0 ? perf_duration_warn+0x30/0x30 remote_function+0x4d/0x60 __flush_smp_call_function_queue+0xc4/0x500 flush_smp_call_function_queue+0x11d/0x1b0 do_idle+0x18f/0x2d0 cpu_startup_entry+0x19/0x20 start_secondary+0x121/0x160 secondary_startup_64_no_verify+0xe5/0xeb </TASK>

amd_pmu_disable_all()/amd_pmu_enable_all() calls inside perf NMI handler were recently added as part of BRS enablement but I'm not sure whether we really need them. We can just disable BRS in the beginning and enable it back while returning from NMI. This will solve the issue by not enabling those events whose active_masks are set but are not yet enabled in hw pmu.

Fixes: ada543459cab ("perf/x86/amd: Add AMD Fam19h Branch Sampling support") Reported-by: Linux Kernel Functional Testing lkft@linaro.org Signed-off-by: Ravi Bangoria ravi.bangoria@amd.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20221114044029.373-1-ravi.bangoria@amd.com

Signed-off-by: Luo Gengkun luogengkun2@huawei.com --- arch/x86/events/amd/core.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c index 2c082abb930b..3127519281f5 100644 --- a/arch/x86/events/amd/core.c +++ b/arch/x86/events/amd/core.c @@ -900,8 +900,7 @@ static int amd_pmu_handle_irq(struct pt_regs *regs) pmu_enabled = cpuc->enabled; cpuc->enabled = 0;

- /* stop everything (includes BRS) */ - amd_pmu_disable_all(); + amd_brs_disable_all();

/* Drain BRS is in use (could be inactive) */ if (cpuc->lbr_users) @@ -912,7 +911,7 @@ static int amd_pmu_handle_irq(struct pt_regs *regs)

cpuc->enabled = pmu_enabled; if (pmu_enabled) - amd_pmu_enable_all(0); + amd_brs_enable_all();

return amd_pmu_adjust_nmi_window(handled); }