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

[Michael S. Tsirkin]

On Mon, Jan 16, 2017 at 04:32:24PM +0800, Peter Xu wrote:
> 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

I prefer not to duplicate data, yes.