Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 updates from Will Deacon:
 "Here's the usual mixed bag of arm64 updates, also including some
  related EFI changes (Acked by Matt) and the MMU gather range cleanup
  (Acked by you).

  Changes include:
   - support for alternative instruction patching from Andre
   - seccomp from Akashi
   - some AArch32 instruction emulation, required by the Android folks
   - optimisations for exception entry/exit code, cmpxchg, pcpu atomics
   - mmu_gather range calculations moved into core code
   - EFI updates from Ard, including long-awaited SMBIOS support
   - /proc/cpuinfo fixes to align with the format used by arch/arm/
   - a few non-critical fixes across the architecture"

* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (70 commits)
  arm64: remove the unnecessary arm64_swiotlb_init()
  arm64: add module support for alternatives fixups
  arm64: perf: Prevent wraparound during overflow
  arm64/include/asm: Fixed a warning about 'struct pt_regs'
  arm64: Provide a namespace to NCAPS
  arm64: bpf: lift restriction on last instruction
  arm64: Implement support for read-mostly sections
  arm64: compat: align cacheflush syscall with arch/arm
  arm64: add seccomp support
  arm64: add SIGSYS siginfo for compat task
  arm64: add seccomp syscall for compat task
  asm-generic: add generic seccomp.h for secure computing mode 1
  arm64: ptrace: allow tracer to skip a system call
  arm64: ptrace: add NT_ARM_SYSTEM_CALL regset
  arm64: Move some head.text functions to executable section
  arm64: jump labels: NOP out NOP -> NOP replacement
  arm64: add support to dump the kernel page tables
  arm64: Add FIX_HOLE to permanent fixed addresses
  arm64: alternatives: fix pr_fmt string for consistency
  arm64: vmlinux.lds.S: don't discard .exit.* sections at link-time
  ...

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index aa29ecb4f800..25a5308744b1 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -169,8 +169,14 @@ armpmu_event_set_period(struct perf_event *event,
 		ret = 1;
 	}
 
-	if (left > (s64)armpmu->max_period)
-		left = armpmu->max_period;
+	/*
+	 * Limit the maximum period to prevent the counter value
+	 * from overtaking the one we are about to program. In
+	 * effect we are reducing max_period to account for
+	 * interrupt latency (and we are being very conservative).
+	 */
+	if (left > (armpmu->max_period >> 1))
+		left = armpmu->max_period >> 1;
 
 	local64_set(&hwc->prev_count, (u64)-left);