linux-kernel - Re: [PATCH 1/5] KVM: vmx: fix ept reserved bits for 1-GByte page

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Message-ID: <53F2EA9B.5010208@redhat.com>
Date:	Tue, 19 Aug 2014 08:11:39 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Gleb Natapov <gleb@...nel.org>, hpa@...or.com, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] KVM: vmx: fix ept reserved bits for 1-GByte page

Il 19/08/2014 04:17, Wanpeng Li ha scritto:
>>> >> -		if (level == 1 || (level == 2 && (spte & (1ULL << 7)))) {
>>> >> +		if (level == 1 || ((level == 3 || level == 2)
>>> >> +				&& (spte & (1ULL << 7)))) {
>> >
>> >This condition can be simplified by checking the return value of ept_rsvd_mask.
>> >If it includes 0x38, this is a large page.

Oops, a "not" was missing. If it includes 0x38, this is _not_ a large
page (it is a page directory / page directory pointer / PML4).

>> Otherwise it is a leaf page and
>> you can go down the "if".
> As you know, 5:3 bits which used for EPT MT are not reserved bits, so 
> I fail to understand why check the return value of ept_rsvd_mask and 
> it's a large page if includes 0x38. Could you eplain in more details? ;-)

A non-leaf page will always have 0x38 in the ept_rsvd_mask.  A leaf page
will never have 0x38 in the ept_rsvd_mask.

Paolo
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