linux-kernel - Re: [PATCH] KVM: MMU: fix huge page adapted on non-PAE host

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Message-ID: <4FC363EE.6060204@linux.vnet.ibm.com>
Date:	Mon, 28 May 2012 19:39:26 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: MMU: fix huge page adapted on non-PAE host

On 05/28/2012 06:57 PM, Avi Kivity wrote:

> On 05/28/2012 09:10 AM, Xiao Guangrong wrote:
>> The huge page size is 4M on non-PAE host, but 2M page size is used in
>> transparent_hugepage_adjust(), so the page we get after adjust the
>> mapping level is not the head page, the BUG_ON() will be triggered
>>
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 72102e0..be3cea4 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -2595,8 +2595,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
>>  			*gfnp = gfn;
>>  			kvm_release_pfn_clean(pfn);
>>  			pfn &= ~mask;
>> -			if (!get_page_unless_zero(pfn_to_page(pfn)))
>> -				BUG();
>> +			kvm_get_pfn(pfn);
>>  			*pfnp = pfn;
>>  		}
>>  	}
> 
> Shouldn't we adjust mask instead?
> 


Adjusting mask to map the whole 4M huge page to KVM guest?
But it seams 4M page size is not supported on VMX/SVM.

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