From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH 2/3] add SPTE_HOST_WRITEABLE flag to the shadow ptes
Date: Mon, 14 Sep 2009 08:18:56 +0300
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References: <1252600738-9456-1-git-send-email-ieidus@redhat.com> <1252600738-9456-2-git-send-email-ieidus@redhat.com> <1252600738-9456-3-git-send-email-ieidus@redhat.com>
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Cc: kvm@vger.kernel.org, aarcange@redhat.com
To: Izik Eidus <ieidus@redhat.com>
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On 09/10/2009 07:38 PM, Izik Eidus wrote:
> this flag notify that the host physical page we are pointing to from
> the spte is write protected, and therefore we cant change its access
> to be write unless we run get_user_pages(write = 1).
>
> (this is needed for change_pte support in kvm)
>
>
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 62d2f86..a7151b8 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -156,6 +156,8 @@ module_param(oos_shadow, bool, 0644);
>   #define CREATE_TRACE_POINTS
>   #include "mmutrace.h"
>
> +#define SPTE_HOST_WRITEABLE (1ULL<<  PT_FIRST_AVAIL_BITS_SHIFT)
> +
>    

Luckilly, this bit is available on EPT too.

>   #define SHADOW_PT_INDEX(addr, level) PT64_I
> @@ -595,9 +600,16 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>
>   		nr_present++;
>   		pte_access = sp->role.access&  FNAME(gpte_access)(vcpu, gpte);
> +		if (!(sp->spt[i]&  SPTE_HOST_WRITEABLE)) {
> + 			pte_access&= ~PT_WRITABLE_MASK;
>    

pte_access uses ACC_ masks, not PT_ masks.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.