Re: [PATCH] KVM: arm64: Avoid naming collision in tracing

[Mostafa Saleh <smostafa@google.com>]

Hi Fuad,

On Sun, Jul 12, 2026 at 05:19:22PM +0100, Fuad Tabba wrote:
> Hi Mostafa,
> 
> On Sun, 12 Jul 2026 at 16:38, Mostafa Saleh <smostafa@google.com> wrote:
> >
> > When the hypervisor tracing (CONFIG_NVHE_EL2_TRACING) is disabled, it
> > defines a static inline stub for trace_clock().
> >
> > However, trace_clock() is already declared as an extern function in
> > linux/trace_clock.h which is pulled in EL2 compilation.
> 
> The rename itself looks correct and complete: all three sites (the
> declarations and stubs in nvhe/clock.h, the definitions in clock.c,
> and the two callers in trace.c) are updated, and no other reference to
> the old names remains under arch/arm64/kvm.
> 
> Two small things...
> 
> >
> > If the file <nvhe/clock.h> is included when CONFIG_NVHE_EL2_TRACING
> > is disabled (by including it manually in setup.c) it will cause:
> > In file included from arch/arm64/kvm/hyp/nvhe/setup.c:22:
> >
> > ./arch/arm64/kvm/hyp/include/nvhe/clock.h:14:19: error: static declaration of ‘trace_clock’ follows non-static declaration
> >
> >    14 | static inline u64 trace_clock(void) { return 0; }
> >
> >       |                   ^~~~~~~~~~~
> >
> > on GCC and a linker error on LLVM (it seems to change the linkage to
> > global)
> >
> > Although that is not a problem at the moment, as no other files
> > include <nvhe/clock.h>. That does not seem to be the intent of
> > this code and that will cause issues with more users as the SMMUv3
> > driver.
> >
> > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> >
> > --
> 
> git am only treats a three-dash "---" line as the scissors; the "--"
> here is two dashes, so mailinfo keeps everything above the diffstat.
> Worth a "---" on the repost so the note stays out of the log.
> 

ops, I will fix that.


> > I did not add Fixes tag as this is currently dormant and not breaking
> > anything.
> > ---
> >  arch/arm64/kvm/hyp/include/nvhe/clock.h | 8 ++++----
> >  arch/arm64/kvm/hyp/nvhe/clock.c         | 4 ++--
> >  arch/arm64/kvm/hyp/nvhe/trace.c         | 4 ++--
> >  3 files changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/include/nvhe/clock.h b/arch/arm64/kvm/hyp/include/nvhe/clock.h
> > index 9f429f5c0664..c2ccd0e8bf22 100644
> > --- a/arch/arm64/kvm/hyp/include/nvhe/clock.h
> > +++ b/arch/arm64/kvm/hyp/include/nvhe/clock.h
> > @@ -6,11 +6,11 @@
> >  #include <asm/kvm_hyp.h>
> >
> >  #ifdef CONFIG_NVHE_EL2_TRACING
> > -void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
> > -u64 trace_clock(void);
> > +void hyp_trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
> > +u64 hyp_trace_clock(void);
> 
> hyp_trace_clock overlaps the host side: arch/arm64/kvm/hyp_trace.c
> already has a struct hyp_trace_clock and static helpers
> hyp_trace_clock_enable() / hyp_trace_clock_show() for the debugfs view
> of the same clock. No actual collision, so this is only a readability
> point, but a reader grepping hyp_trace_clock now gets two unrelated
> things. Maybe you'd want to consider a different name, but naming is
> hard :)

Yes, that shouldn't be a problem,  I just added hyp_ prefix, but I
am ok with any suggestions!

Thanks,
Mostafa

> 
> Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
> Tested-by: Fuad Tabba < fuad.tabba@linux.dev>
> 
> Test: builds fine with the different config enables.
> 
> Cheers,
> /fuad