Re: [PATCH] x86/irq: hide HYP in /proc/interrupts when not on Xen/Hyper-V

[Ingo Molnar <mingo@kernel.org>]

* Vitaly Kuznetsov <vkuznets@redhat.com> wrote:

> Ingo Molnar <mingo@kernel.org> writes:
> 
> > * Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> >
> >> Hypervisor callback interrupts are only accounted on Xen/Hyper-V and we
> >> detect hypervisor's type in early boot. There is no point in having
> >> always-zero HYP: line on other hypervisors or bare metal.
> >> 
> >> Suggested-by: Radim Krčmář <rkrcmar@redhat.com>
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> >> ---
> >>  arch/x86/kernel/irq.c | 13 +++++++++----
> >>  1 file changed, 9 insertions(+), 4 deletions(-)
> >> 
> >> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> >> index 88b36648..0c82064 100644
> >> --- a/arch/x86/kernel/irq.c
> >> +++ b/arch/x86/kernel/irq.c
> >> @@ -18,6 +18,7 @@
> >>  #include <asm/mce.h>
> >>  #include <asm/hw_irq.h>
> >>  #include <asm/desc.h>
> >> +#include <asm/hypervisor.h>
> >>  
> >>  #define CREATE_TRACE_POINTS
> >>  #include <asm/trace/irq_vectors.h>
> >> @@ -139,10 +140,14 @@ int arch_show_interrupts(struct seq_file *p, int prec)
> >>  	seq_puts(p, "  Machine check polls\n");
> >>  #endif
> >>  #if IS_ENABLED(CONFIG_HYPERV) || defined(CONFIG_XEN)
> >> -	seq_printf(p, "%*s: ", prec, "HYP");
> >> -	for_each_online_cpu(j)
> >> -		seq_printf(p, "%10u ", irq_stats(j)->irq_hv_callback_count);
> >> -	seq_puts(p, "  Hypervisor callback interrupts\n");
> >> +	if (x86_hyper == &x86_hyper_ms_hyperv ||
> >> +	    x86_hyper == &x86_hyper_xen) {
> >> +		seq_printf(p, "%*s: ", prec, "HYP");
> >> +		for_each_online_cpu(j)
> >> +			seq_printf(p, "%10u ",
> >> +				   irq_stats(j)->irq_hv_callback_count);
> >> +		seq_puts(p, "  Hypervisor callback interrupts\n");
> >> +	}
> >
> > So I think we should simplify this to:
> >
> > 	if (x86_hyper) {
> > 		...
> > 	}
> >
> > this will print the HYP line on hypervisors that don't use 
> > HYPERVISOR_CALLBACK_VECTOR, but it will make it a lot more self-maintaining, we 
> > won't accidentally skip this line on hypervisors that start using the callback 
> > IRQ.
> 
> I was under an impression KVM and Vmware don't use these hypervisor
> callback irqs 'by desing' and even if one day they start using it
> someone will have to put inc_irq_stat() somewhere.
> 
> If the goal is to avoid having x86_hyper_ms_hyperv/x86_hyper_xen in
> irq.c we can follow Andrew's suggestion and add a flag
> (use_callback_irqs?) to struct hypervisor_x86.

Yeah, a flag would be nicer, and that flag should also be used somewhere else - 
for example in the IRQ vector init code or so?

I.e. make it only possible to use the callback vector if the flag is set properly 
- or something like that. That way there will never be a mismatch between flag and 
reality.

Thanks,

	Ingo