Re: [Qemu-devel] [PATCH RFC v3 13/14] intel_iommu: allow dynamic switch of IOMMU region

[Jason Wang <jasowang@redhat.com>]

On 2017年01月16日 16:12, Peter Xu wrote:
> On Mon, Jan 16, 2017 at 04:01:00PM +0800, Jason Wang wrote:
>>
>> On 2017年01月16日 15:50, Peter Xu wrote:
>>> On Mon, Jan 16, 2017 at 02:20:31PM +0800, Jason Wang wrote:
>>>
>>> [...]
>>>
>>>>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>>>>> index fd75112..2596f11 100644
>>>>> --- a/hw/i386/intel_iommu.c
>>>>> +++ b/hw/i386/intel_iommu.c
>>>>> @@ -1343,9 +1343,49 @@ static void vtd_handle_gcmd_sirtp(IntelIOMMUState *s)
>>>>>       vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_IRTPS);
>>>>>   }
>>>>> +static void vtd_switch_address_space(VTDAddressSpace *as, bool iommu_enabled)
>>>> Looks like you can check s->dmar_enabled here?
>>> Yes, we need to check old state in case we don't need a switch at all.
>>> Actually I checked it...
>>>
>> I mean is there a chance that iommu_enabled( better name should be
>> dmar_enabled) is not equal to s->dmar_enabled? Looks not.
>>
>> vtd_handle_gcmd_te() did:
>>
>>      ...
>>      if (en) {
>>          s->dmar_enabled = true;
>>          /* Ok - report back to driver */
>>          vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_TES);
>>      } else {
>>          s->dmar_enabled = false;
>>      ...
>>
>> You can vtd_switch_address_space_all(s, en) after this which will call this
>> function. And another caller like you've pointed out has already call this
>> through s->dmar_enabled. So en here is always s->dmar_enalbed?
> Hmm, yes...
>
> (I would still prefer keeping this parameter for readablility.
>   Though, I prefer your suggestion to rename it to dmar_enabled)
>
> -- peterx

I think this does not give more readability :) May I was wrong, let 
leave this for maintainer.

Thanks :)