linux-kernel - Re: [PATCH 07/11] Retry fault before vmentry

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Message-ID: <4AEED8A8.9030606@redhat.com>
Date:	Mon, 02 Nov 2009 15:03:36 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/11] Retry fault before vmentry

On 11/01/2009 01:56 PM, Gleb Natapov wrote:
> When page is swapped in it is mapped into guest memory only after guest
> tries to access it again and generate another fault. To save this fault
> we can map it immediately since we know that guest is going to access
> the page.
>
>    
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 9fe2ecd..b1fe61f 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -375,7 +375,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
>    *  Returns: 1 if we need to emulate the instruction, 0 otherwise, or
>    *           a negative value on error.
>    */
> -static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
> +static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t cr3, gva_t addr,
>   			       u32 error_code)
>   {
>   	int write_fault = error_code&  PFERR_WRITE_MASK;
> @@ -388,6 +388,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
>   	pfn_t pfn;
>   	int level = PT_PAGE_TABLE_LEVEL;
>   	unsigned long mmu_seq;
> +	gpa_t curr_cr3 = vcpu->arch.cr3;
>
>   	pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
>   	kvm_mmu_audit(vcpu, "pre page fault");
> @@ -396,6 +397,13 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
>   	if (r)
>   		return r;
>
> +	if (curr_cr3 != cr3) {
> +		vcpu->arch.cr3 = cr3;
> +		paging_new_cr3(vcpu);
> +		if (kvm_mmu_reload(vcpu))
> +			goto switch_cr3;
> +	}
> +
>    

This is a little frightening.  I can't put my finger on anything 
though.  But playing with cr3 under the guest's feet worries me.

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

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