linux-kernel - Re: [PATCH v2 02/15] KVM: MMU: properly check last spte in fast_page

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Date:	Mon, 30 Sep 2013 18:23:08 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	gleb@...hat.com, avi.kivity@...il.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 02/15] KVM: MMU: properly check last spte in
 fast_page_fault()

On Thu, Sep 05, 2013 at 06:29:05PM +0800, Xiao Guangrong wrote:
> Using sp->role.level instead of @level since @level is not got from the
> page table hierarchy
> 
> There is no issue in current code since the fast page fault currently only
> fixes the fault caused by dirty-log that is always on the last level
> (level = 1)
> 
> This patch makes the code more readable and avoids potential issue in the
> further development
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 7714fd8..869f1db 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2804,9 +2804,9 @@ static bool page_fault_can_be_fast(u32 error_code)
>  }
>  
>  static bool
> -fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 spte)
> +fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> +			u64 *sptep, u64 spte)
>  {
> -	struct kvm_mmu_page *sp = page_header(__pa(sptep));
>  	gfn_t gfn;
>  
>  	WARN_ON(!sp->role.direct);
> @@ -2832,6 +2832,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
>  			    u32 error_code)
>  {
>  	struct kvm_shadow_walk_iterator iterator;
> +	struct kvm_mmu_page *sp;
>  	bool ret = false;
>  	u64 spte = 0ull;
>  
> @@ -2852,7 +2853,8 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
>  		goto exit;
>  	}
>  
> -	if (!is_last_spte(spte, level))
> +	sp = page_header(__pa(iterator.sptep));
> +	if (!is_last_spte(spte, sp->role.level))
>  		goto exit;
>  
>  	/*
> @@ -2878,7 +2880,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
>  	 * the gfn is not stable for indirect shadow page.
>  	 * See Documentation/virtual/kvm/locking.txt to get more detail.
>  	 */
> -	ret = fast_pf_fix_direct_spte(vcpu, iterator.sptep, spte);
> +	ret = fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte);
>  exit:
>  	trace_fast_page_fault(vcpu, gva, error_code, iterator.sptep,
>  			      spte, ret);
> -- 
> 1.8.1.4

Unrelated to this patch:

If vcpu->mode = OUTSIDE_GUEST_MODE, no IPI is sent
by kvm_flush_remote_tlbs.

So how is this supposed to work again?

        /*
         * Wait for all vcpus to exit guest mode and/or lockless shadow
         * page table walks.
         */
        kvm_flush_remote_tlbs(kvm);

Patch looks fine.

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