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

[Peter Xu]

On Mon, Jan 16, 2017 at 04:25:35PM +0800, Jason Wang wrote:
> 
> 
> 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 :)

Thanks for reviewing this series so fast!

I have no strong opinion as well. Maybe you are right. :-)

Michael, please let me know if you dislike this, so I can remove this
parameter (it equals to as->iommu_state->dmar_enabled).

Thanks,

-- peterx