Re: [PATCH 1/4] x86/entry: Remove unwanted instrumentation in common_interrupt()

[Alexander Potapenko]

On Tue, Jun 4, 2024 at 3:45 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> common_interrupt() and friends call kvm_set_cpu_l1tf_flush_l1d(),
> which is not marked as noinstr nor __always_inline.
> So compiler outlines it and adds instrumentation to it.
> Since the call is inside of instrumentation_begin/end(),
> objtool does not warn about it.
>
> The manifestation is that KCOV produces spurious coverage
> in kvm_set_cpu_l1tf_flush_l1d() in random places because
> the call happens when preempt count is not yet updated
> to say that we are in an interrupt.
>
> Mark kvm_set_cpu_l1tf_flush_l1d() as __always_inline and move
> out of instrumentation_begin/end() section.
> It only calls __this_cpu_write() which is already safe to call
> in noinstr contexts.
>
> Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>