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Subject[PATCH 4/9] x86, perf: Explicitly optimize vm86 handling in code_segment_base
Date
There's no point in checking the VM bit on 64-bit, and, since we're
explicitly checking it, we can use user_mode_ignore_vm86 after the
check.

While we're at it, rearrange the ifdef slightly to make the code
flow a bit clearer.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/kernel/cpu/perf_event.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 979963bb3977..56f7e60ad732 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2147,18 +2147,19 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
static unsigned long code_segment_base(struct pt_regs *regs)
{
/*
+ * For IA32 we look at the GDT/LDT segment base to convert the
+ * effective IP to a linear address.
+ */
+
+#ifdef CONFIG_X86_32
+ /*
* If we are in VM86 mode, add the segment offset to convert to a
* linear address.
*/
if (regs->flags & X86_VM_MASK)
return 0x10 * regs->cs;

- /*
- * For IA32 we look at the GDT/LDT segment base to convert the
- * effective IP to a linear address.
- */
-#ifdef CONFIG_X86_32
- if (user_mode(regs) && regs->cs != __USER_CS)
+ if (user_mode_ignore_vm86(regs) && regs->cs != __USER_CS)
return get_segment_base(regs->cs);
#else
if (user_mode(regs) && !user_64bit_mode(regs) &&
--
2.3.0


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