linux-kernel - Re: [PATCH v2 12/13] KVM: x86: add SMM to the MMU role, support SMRAM address space

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Date:	Wed, 17 Jun 2015 10:18:23 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
CC:	rkrcmar@...hat.com, bdas@...hat.com
Subject: Re: [PATCH v2 12/13] KVM: x86: add SMM to the MMU role, support SMRAM
 address space



On 09/06/2015 06:01, Xiao Guangrong wrote:
> 
> 
> On 05/28/2015 01:05 AM, Paolo Bonzini wrote:
>> This is now very simple to do.  The only interesting part is a simple
>> trick to find the right memslot in gfn_to_rmap, retrieving the address
>> space from the spte role word.  The same trick is used in the auditing
>> code.
>>
>> The comment on top of union kvm_mmu_page_role has been stale forever,
> 
> Fortunately, we have documented these fields in mmu.txt, please do it for
> 'smm' as well. :)

Right, done.

>> +        /*
>> +         * This is left at the top of the word so that
>> +         * kvm_memslots_for_spte_role can extract it with a
>> +         * simple shift.  While there is room, give it a whole
>> +         * byte so it is also faster to load it from memory.
>> +         */
>> +        unsigned smm:8;
> 
> I suspect if we really need this trick, smm is not the hottest filed in
> this struct anyway.

Note that after these patches it is used by gfn_to_rmap, and hence for
example rmap_add.

Paolo
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