linux-kernel - Re: [PATCH 4/7] KVM: MMU: document mmio page fault

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Date:	Wed, 19 Jun 2013 20:59:58 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	gleb@...hat.com, avi.kivity@...il.com, mtosatti@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 4/7] KVM: MMU: document mmio page fault

On 06/19/2013 08:10 PM, Paolo Bonzini wrote:
> Il 19/06/2013 11:09, Xiao Guangrong ha scritto:
>> Document it to Documentation/virtual/kvm/mmu.txt
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> ---
>>  Documentation/virtual/kvm/mmu.txt | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
>> index 5a6b2e2..4fb442b 100644
>> --- a/Documentation/virtual/kvm/mmu.txt
>> +++ b/Documentation/virtual/kvm/mmu.txt
>> @@ -270,14 +270,21 @@ This is the most complicated event.  The cause of a page fault can be:
>>  
>>  Handling a page fault is performed as follows:
>>  
>> + - if the RSV bit of the error code is set, the page fault is caused by guest
>> +   accessing MMIO, walk shadow page table to get the last spte where the mmio
>> +   information is stored and cache the information to vcpu->arch.mmio_gva,
>> +   vcpu->arch.access and vcpu->arch.mmio_gfn then call the emulator to emulate
>> +   the instruction who will get the benefit from the cached mmio info
> 
> + - if the RSV bit of the error code is set, the page fault is caused by guest
> +   accessing MMIO and cached MMIO information is available.
> +   - walk shadow page table
> +   - cache the information to vcpu->arch.mmio_gva, vcpu->arch.access and
> +     vcpu->arch.mmio_gfn, and call the emulator

Nice.

> 
>>   - if needed, walk the guest page tables to determine the guest translation
>>     (gva->gpa or ngpa->gpa)
>>     - if permissions are insufficient, reflect the fault back to the guest
>>   - determine the host page
>> -   - if this is an mmio request, there is no host page; call the emulator
>> -     to emulate the instruction instead
>> +   - if this is an mmio request, there is no host page; cache the info to
>> +     vcpu->arch.mmio_gva, vcpu->arch.access and vcpu->arch.mmio_gfn
>>   - walk the shadow page table to find the spte for the translation,
>>     instantiating missing intermediate page tables as necessary
>> +   - If this is an mmio request, cache the mmio info to the spte and set some
>> +     reserved bits on the spte
> 
> Added "(see callers of kvm_mmu_set_mmio_spte_mask)".  Not really related, but
> just came to my mind: perhaps we can have a section on A/D bits too.

It is useful i think. Will do it.

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