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

[Peter Xu <peterx@redhat.com>]

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