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

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Date:	Tue, 07 Jul 2015 15:45:30 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Radim Krčmář <rkrcmar@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH] x86/irq: hide HYP in /proc/interrupts when not on Xen/Hyper-V

Ingo Molnar <mingo@...nel.org> writes:

> * Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
>> Ingo Molnar <mingo@...nel.org> writes:
>> 
>> > * Vitaly Kuznetsov <vkuznets@...hat.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@...hat.com>
>> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.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.

Actually we already have the flag :-) Both Xen and Hyper-V do
alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, ...) so we can simply do
test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors) here. It feels a
little bit hackish but it checks what we need to check.

-- 
  Vitaly
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