linux-kernel - Re: [PATCH] KVM: vmx: speed up MSR bitmap merge

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Message-ID: <854645993.27733836.1513612982078.JavaMail.zimbra@redhat.com>
Date:   Mon, 18 Dec 2017 11:03:02 -0500 (EST)
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, bsd@...hat.com,
        jmattson@...gle.com
Subject: Re: [PATCH] KVM: vmx: speed up MSR bitmap merge


> > -	memset(msr_bitmap_l0, 0xff, PAGE_SIZE);
> > +	msr_bitmap_l1 = (unsigned long *)kmap(page);
> 
> Wouldn't it be easier to simply set everything to 0xff as before and
> then only handle the one special case where you don't do that? e.g. the
> complete else part would be gone.

It can change from one vmentry to the next, so I'm not sure how you'd
do that.

> > +	nested_vmx_disable_intercept_for_msr(
> > +		msr_bitmap_l1, msr_bitmap_l0,
> > +		APIC_BASE_MSR + (APIC_TASKPRI >> 4),
> > +		MSR_TYPE_W);
> 
> I'd vote for indenting the parameters properly (even though we exceed 80
> chars by 1 then :) )

Ok, will do.  Regarding the WARN, I'm undecided.  I like the idea of not
calling a function that works on MSR bitmaps unless you have one...

Paolo