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Date: Fri, 30 Mar 2012 13:01:47 +0800
From: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
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To: Avi Kivity <avi@redhat.com>
CC: Marcelo Tosatti <mtosatti@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH 04/13] KVM: MMU: introduce FNAME(get_sp_gpa)
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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?

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;
}