Re: [PATCH v7 4/5] x86: perf: Refactor misc flag assignments

[Colton Lewis]

Peter Zijlstra <pet...@infradead.org> writes:

On Thu, Nov 07, 2024 at 07:03:35PM +0000, Colton Lewis wrote:

Break the assignment logic for misc flags into their own respective
functions to reduce the complexity of the nested logic.

Signed-off-by: Colton Lewis <coltonle...@google.com>
Reviewed-by: Oliver Upton <oliver.up...@linux.dev>
---
  arch/x86/events/core.c            | 32 +++++++++++++++++++++++--------
  arch/x86/include/asm/perf_event.h |  2 ++
  2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d19e939f3998..9fdc5fa22c66 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c

@@ -3011,16 +3011,35 @@ unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)

        return regs->ip + code_segment_base(regs);
  }

+static unsigned long common_misc_flags(struct pt_regs *regs)
+{
+       if (regs->flags & PERF_EFLAGS_EXACT)
+               return PERF_RECORD_MISC_EXACT_IP;
+
+       return 0;
+}
+
+unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
+{
+       unsigned long guest_state = perf_guest_state();
+       unsigned long flags = common_misc_flags(regs);

This is double common_misc and makes no sense

I'm confused what you mean. Are you referring to starting with
common_misc_flags in both perf_arch_misc_flags and
perf_arch_guest_misc_flags so possibly the common_msic_flags are set
twice?

That seems like a good thing that common flags are set wherever they
apply. You can't guarantee where perf_arch_guest_misc_flags may be
called in the future.

+
+       if (!(guest_state & PERF_GUEST_ACTIVE))
+               return flags;
+
+       if (guest_state & PERF_GUEST_USER)
+               return flags & PERF_RECORD_MISC_GUEST_USER;
+       else
+               return flags & PERF_RECORD_MISC_GUEST_KERNEL;

And this is just broken garbage, right?

+}

Did you mean to write:

unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
{
        unsigned long guest_state = perf_guest_state();
        unsigned long flags = 0;

        if (guest_state & PERF_GUEST_ACTIVE) {
                if (guest_state & PERF_GUEST_USER)
                        flags |= PERF_RECORD_MISC_GUEST_USER;
                else
                        flags |= PERF_RECORD_MISC_GUEST_KERNEL;
        }

        return flags;
}

Ok, my mistake was using & instead of |, but the branches are
functionally the same.

I'll use something closer to your suggestion.

  unsigned long perf_arch_misc_flags(struct pt_regs *regs)
  {
        unsigned int guest_state = perf_guest_state();
-       int misc = 0;
+       unsigned long misc = common_misc_flags(regs);

Because here you do the common thing..

        if (guest_state) {
-               if (guest_state & PERF_GUEST_USER)
-                       misc |= PERF_RECORD_MISC_GUEST_USER;
-               else
-                       misc |= PERF_RECORD_MISC_GUEST_KERNEL;
+               misc |= perf_arch_guest_misc_flags(regs);

And here you mix in the guest things.

        } else {
                if (user_mode(regs))
                        misc |= PERF_RECORD_MISC_USER;