linux-kernel - Re: [PATCHv7 3/8] kvm_para: guest side for eoi avoidance

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Date:	Mon, 18 Jun 2012 18:01:59 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	x86@...nel.org, kvm@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, gleb@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv7 3/8] kvm_para: guest side for eoi avoidance

On 06/18/2012 05:50 PM, Michael S. Tsirkin wrote:
> 
>> >  
>> > +/* size alignment is implied but just to make it explicit. */
>> > +static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) __aligned(2) =
>> > +	KVM_PV_EOI_DISABLED;
>> 
>> You're actually breaking the alignment.  ulong has 8 byte alignment
>> sometimes and you can make it cross cache boundary this way.
> 
> No, if you look at the definition of __aligned
> you will see that it limits the alignment from below.
> Compiler still applies the natural size alignment.
> You are not the first to get confused. So I wonder: is it better
> to add a comment or simply remove __aligned here.

Both.

>> >  
>> > +	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
>> > +		__get_cpu_var(kvm_apic_eoi) = 0;
>> > +		wrmsrl(MSR_KVM_PV_EOI_EN, __pa(&__get_cpu_var(kvm_apic_eoi)) |
>> > +		       KVM_MSR_ENABLED);
>> 
>> Bad formatting.
> 
> I guess temporary will make it prettier.
> 	unsigned long pa;
> 	__get_cpu_var(kvm_apic_eoi) = 0;
> 	pa = __pa(&__get_cpu_var(kvm_apic_eoi)) | KVM_MSR_ENABLED;
> 	wrmsrl(MSR_KVM_PV_EOI_EN, pa);

That, or

+		wrmsrl(MSR_KVM_PV_EOI_EN,
+                      __pa(&__get_cpu_var(kvm_apic_eoi)) | _ENABLED);

You have an argument split over two lines with no helpful indentation to
show this.

>> 
>> 
>> Please check that the kexec path also disables pveoi.
> 
> The chunk in kvm_pv_guest_cpu_reboot does this, doesn't it?

Dunno, does it?



-- 
error compiling committee.c: too many arguments to function


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