linux-kernel - Re: [PATCH 04/13] KVM: MMU: introduce FNAME(get_sp

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Message-ID: <4F784D31.4070206@redhat.com>
Date:	Sun, 01 Apr 2012 15:42:25 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 04/13] KVM: MMU: introduce FNAME(get_sp_gpa)

On 03/30/2012 08:01 AM, Xiao Guangrong wrote:
> On 03/29/2012 09:07 PM, Avi Kivity wrote:
>
> > On 03/29/2012 11:22 AM, Xiao Guangrong wrote:
> >> It can calculate the base gpa of the specified shadow page on any level,
> >> let it instead of FNAME(get_level1_sp_gpa)
> >>
> >>
> >> +static gpa_t FNAME(get_sp_gpa)(struct kvm_mmu_page *sp)
> >> +{
> > 
> > Maybe worth adding a pte index and calling it get_spte_gpa(), depends on
> > the next patches I guess.
> > 
>
>
> Yes.
>
> But FNAME(get_sp_gpa) is still needed by FNAME(sync_page) path which sync
> all sptes. I will introduce get_spte_gpa() as you mentioned which will be
> used in invlpg path and in the later patch.
>
>
> >> +	int offset, shift;
> >> +
> >> +	shift = PAGE_SHIFT - (PT_LEVEL_BITS - PT64_LEVEL_BITS) * sp->role.level;
> >> +	offset = sp->role.quadrant << shift;
> > 
> > if you add '& ~PAGE_MASK' the compiler may be smart enough to drop the
> > whole thing for 64-bit ptes.
> > 
>
>
> Sorry. how to do that?

   offset = (sp->role.quadrant << shift) & ~PAGEMASK;

the compiler should see that shift == PAGE_SHIFT and therefore anything
in sp->role.quadrant will be masked out.

> But if you want to remove the unnecessary workload, i will change it
> like this:
>
> static gpa_t FNAME(get_sp_gpa)(struct kvm_mmu_page *sp)
> {
> 	int offset = 0;
>
> #if PTTYPE == 32
> 	int shift;
>
> 	shift = PAGE_SHIFT - (PT_LEVEL_BITS - PT64_LEVEL_BITS) * sp->role.level;
> 	offset = sp->role.quadrant << shift;
> #endif
> 	return gfn_to_gpa(sp->gfn) + offset;
> }

That works too.

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

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