Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths

[Naveen N. Rao]

Steven Rostedt wrote:

On Mon, 19 Mar 2018 14:43:00 +0530
"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:

diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S 
b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index 3f3e81852422..fdf702b4df25 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -60,6 +60,19 @@ _GLOBAL(ftrace_caller)
        mfxer   r10
        mfcr    r11

+#ifdef CONFIG_KVM

+       lbz     r3, PACA_FTRACE_DISABLED(r13)
+       cmpdi   r3, 0
+       beq     1f
+       mflr    r3
+       mtctr   r3
+       REST_GPR(3, r1)
+       addi    r1, r1, SWITCH_FRAME_SIZE
+       mtlr    r0
+       bctr
+1:
+#endif

I wonder if we should try to move the return out of the fast path (for
cache reasons), as most of the time the above compare will be true. That
is:

#ifdef CONFIG_KVM
        lbz     r3, PACA_FTRACE_DISABLED(r13)
        cmpdi   r3, 0
        bne     no_trace
#endif

/* rest of ftrace_caller code */

/* after ftrace_caller... */
        bctr                    /* jump after _mcount site */

#ifdef  CONFIG_KVM
no_trace:
        mflr    r3
        mtctr   r3
        REST_GPR(3, r1)
        addi    r1, r1, SWITCH_FRAME_SIZE
        mtlr    r0
        bctr
#endif

Thanks, I'll incorporate those changes in my next version.

- Naveen