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

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Message-ID: <55826D11.2060801@redhat.com>
Date:	Thu, 18 Jun 2015 09:02:41 +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 18/06/2015 07:02, Xiao Guangrong wrote:
> However, role->level is more hotter than role->smm so that it's also a good
> candidate for this kind of trick.

Right, we could give the first 8 bits to role->level, so it can be
accessed with a single memory load and extracted with a single AND.
Those two are definitely the hottest fields.

> And this is only 32 bits which can be operated in a CPU register by a
> single memory load, that is why i was worried if it is really needed.

However, an 8-bit field can be loaded from memory with a single movz
instruction.

Paolo
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