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

[Vincent Donnefort <vdonnefort@google.com>]

On Sun, Jul 12, 2026 at 03:38:35PM +0000, Mostafa Saleh 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.

I am completely unable to reproduce that. CONFIG_NVHE_EL2_TRACING, isn't a
selectable option, it depends on NVHE_EL2_DEBUG.

How does your .config look like?

> 
> 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:

nvhe/clock.h seems already included in setup.c

> 
> ./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>
> 
> --
> 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);
>  #else
>  static inline void
> -trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
> -static inline u64 trace_clock(void) { return 0; }
> +hyp_trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
> +static inline u64 hyp_trace_clock(void) { return 0; }
>  #endif
>  #endif
> diff --git a/arch/arm64/kvm/hyp/nvhe/clock.c b/arch/arm64/kvm/hyp/nvhe/clock.c
> index a7fc61976fd0..8adefb0b696c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/clock.c
> +++ b/arch/arm64/kvm/hyp/nvhe/clock.c
> @@ -30,7 +30,7 @@ static u64 __clock_mult_uint128(u64 cyc, u32 mult, u32 shift)
>  }
>  
>  /* Does not guarantee no reader on the modified bank. */
> -void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
> +void hyp_trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
>  {
>  	struct clock_data *clock = &trace_clock_data;
>  	u64 bank = clock->cur ^ 1;
> @@ -48,7 +48,7 @@ void trace_clock_update(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
>  }
>  
>  /* Use untrusted host data */
> -u64 trace_clock(void)
> +u64 hyp_trace_clock(void)
>  {
>  	struct clock_data *clock = &trace_clock_data;
>  	u64 bank = smp_load_acquire(&clock->cur);
> diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
> index e7e150ab265f..f2a32463c6c2 100644
> --- a/arch/arm64/kvm/hyp/nvhe/trace.c
> +++ b/arch/arm64/kvm/hyp/nvhe/trace.c
> @@ -35,7 +35,7 @@ static bool hyp_trace_buffer_loaded(struct hyp_trace_buffer *trace_buffer)
>  void *tracing_reserve_entry(unsigned long length)
>  {
>  	return simple_ring_buffer_reserve(this_cpu_ptr(trace_buffer.simple_rbs), length,
> -					  trace_clock());
> +					  hyp_trace_clock());
>  }
>  
>  void tracing_commit_entry(void)
> @@ -290,7 +290,7 @@ void __tracing_update_clock(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
>  	}
>  
>  	/* ...we can now override the old one and swap. */
> -	trace_clock_update(mult, shift, epoch_ns, epoch_cyc);
> +	hyp_trace_clock_update(mult, shift, epoch_ns, epoch_cyc);
>  }
>  
>  int __tracing_reset(unsigned int cpu)
> -- 
> 2.55.0.795.g602f6c329a-goog
>