linux-kernel - Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted

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Date:	Mon, 28 Jun 2010 12:50:57 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted

On 06/25/2010 03:06 PM, Xiao Guangrong wrote:
> Consider using small page to fit guest's large page mapping:
>
> If the mapping is writable but the dirty flag is not set, we will find
> the read-only direct sp and setup the mapping, then if the write #PF
> occur, we will mark this mapping writable in the read-only direct sp,
> now, other real read-only mapping will happily write it without #PF.
>
> It may hurt guest's COW
>
> Fixed by re-install the mapping when write #PF occur.
>
> Signed-off-by: Xiao Guangrong<xiaoguangrong@...fujitsu.com>
> ---
>   arch/x86/kvm/mmu.c         |    3 ++-
>   arch/x86/kvm/paging_tmpl.h |   18 ++++++++++++++++++
>   2 files changed, 20 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 556a798..0412ba4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -153,7 +153,8 @@ module_param(oos_shadow, bool, 0644);
>   #define CREATE_TRACE_POINTS
>   #include "mmutrace.h"
>
> -#define SPTE_HOST_WRITEABLE (1ULL<<  PT_FIRST_AVAIL_BITS_SHIFT)
> +#define SPTE_HOST_WRITEABLE	(1ULL<<  PT_FIRST_AVAIL_BITS_SHIFT)
> +#define SPTE_NO_DIRTY		(2ULL<<  PT_FIRST_AVAIL_BITS_SHIFT)
>
>   #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index e46eb8a..fdba751 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -325,6 +325,20 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
>   			break;
>   		}
>
> +		if (*sptep&  SPTE_NO_DIRTY) {
> +			struct kvm_mmu_page *child;
> +
> +			WARN_ON(level !=  gw->level);
> +			WARN_ON(!is_shadow_present_pte(*sptep));
> +			if (dirty) {
> +				child = page_header(*sptep&
> +						      PT64_BASE_ADDR_MASK);
> +				mmu_page_remove_parent_pte(child, sptep);
> +				__set_spte(sptep, shadow_trap_nonpresent_pte);
> +				kvm_flush_remote_tlbs(vcpu->kvm);
> +			}
> +		}
> +
>    

Instead of adding a new bit, can you encode the protection in the direct 
sp's access bits?  So we'll have one sp for read-only or 
writeable-but-not-dirty small pages, and another sp for 
writeable-and-dirty small pages.

-- 
error compiling committee.c: too many arguments to function

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