linux-kernel - Re: [PATCH v5 09/12] Retry fault before vmentry

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Message-ID: <4C73932A.3030709@redhat.com>
Date:	Tue, 24 Aug 2010 12:38:50 +0300
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, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org, mtosatti@...hat.com
Subject: Re: [PATCH v5 09/12] Retry fault before vmentry

  On 08/24/2010 12:33 PM, Gleb Natapov wrote:
>
>
>>> @@ -505,6 +506,37 @@ out_unlock:
>>>   	return 0;
>>>   }
>>>
>>> +static int FNAME(page_fault_other_cr3)(struct kvm_vcpu *vcpu, gpa_t cr3,
>>> +				       gva_t addr, u32 error_code)
>>> +{
>>> +	int r = 0;
>>> +	gpa_t curr_cr3 = vcpu->arch.cr3;
>>> +
>>> +	if (curr_cr3 != cr3) {
>>> +		/*
>>> +		 * We do page fault on behalf of a process that is sleeping
>>> +		 * because of async PF. PV guest takes reference to mm that cr3
>>> +		 * belongs too, so it has to be valid here.
>>> +		 */
>>> +		kvm_set_cr3(vcpu, cr3);
>>> +		if (kvm_mmu_reload(vcpu))
>>> +			goto switch_cr3;
>>> +	}
>> With nested virtualization, we need to switch cr0, cr4, and efer as well...
>>
> On SVM or VMX or both?

Both.  Let's defer this patch since it's an optimization, this is really 
complicated.

>>> +
>>> +	r = FNAME(page_fault)(vcpu, addr, error_code, true);
>>> +
>>> +	if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
>>> +		kvm_mmu_sync_roots(vcpu);
>> Why is this needed?
>>
> http://www.mail-archive.com/kvm@vger.kernel.org/msg37827.html
>
>   KVM_REQ_MMU_SYNC request generated here must be processed before
>   switching to a different cr3 (otherwise vcpu_enter_guest will process it
>   with the wrong cr3 in place).

Ah, it should be part of the cr3 switch block above.

>>> +
>>> +switch_cr3:
>>> +	if (curr_cr3 != vcpu->arch.cr3) {
>>> +		kvm_set_cr3(vcpu, curr_cr3);
>>> +		kvm_mmu_reload(vcpu);
>>> +	}
>>> +
>>> +	return r;
>>> +}
>> This has the nasty effect of flushing the TLB on AMD.
>>
> What is more expansive reenter the guest and handle one more fault, or
> flash TLB here?

No idea.  Probably the reentry.  On Intel the tlb is flushed anyway.

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

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