Re: [PATCH 1/1] iommu/vt-d: Omit devTLB invalidation requests when TES=0

[Baolu Lu]

On 11/14/23 12:45 PM, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, November 14, 2023 11:14 AM
> >
> > On 11/14/23 11:14 AM, Tian, Kevin wrote:
> > > > From: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > > > Sent: Tuesday, November 14, 2023 9:11 AM
> > > >
> > > > The latest VT-d spec indicates that when remapping hardware is disabled
> > > > (TES=0 in Global Status Register), upstream ATS Invalidation Completion
> > > > requests are treated as UR (Unsupported Request).
> > > >
> > > > Consequently, the spec recommends in section 4.3 Handling of Device-TLB
> > > > Invalidations that software refrain from submitting any Device-TLB
> > > > invalidation requests when address remapping hardware is disabled.
> > > >
> > > > Verify address remapping hardware is enabled prior to submitting Device-
> > > > TLB invalidation requests.
> > > >
> > > > Fixes: 792fb43ce2c9 ("iommu/vt-d: Enable Intel IOMMU scalable mode by
> > > > default")
> > > > Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > > > ---
> > > >    drivers/iommu/intel/dmar.c | 18 ++++++++++++++++++
> > > >    1 file changed, 18 insertions(+)
> > > >
> > > > diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> > > > index a3414afe11b0..23cb80d62a9a 100644
> > > > --- a/drivers/iommu/intel/dmar.c
> > > > +++ b/drivers/iommu/intel/dmar.c
> > > > @@ -1522,6 +1522,15 @@ void qi_flush_dev_iotlb(struct intel_iommu
> > > > *iommu, u16 sid, u16 pfsid,
> > > >    {
> > > >    	struct qi_desc desc;
> > > >
> > > > +	/*
> > > > +	 * VT-d spec, section 4.3:
> > > > +	 *
> > > > +	 * Software is recommended to not submit any Device-TLB
> > > > invalidation
> > > > +	 * requests while address remapping hardware is disabled.
> > > > +	 */
> > > > +	if (!(iommu->gcmd & DMA_GCMD_TE))
> > > > +		return;
> > > > +
> > > Is it a valid case to see such request when the iommu is disabled?
> > > If not then let's add a WARN.
> >
> > There might be valid cases. The VT-d translation is turned on after all
> > devices get probed.
>
> but I didn't get why there will be actual mapping changes before
> vtd translation is enabled...

For an example, in iommu_create_device_direct_mappings(),
iommu_flush_iotlb_all() is called after direct mappings are created.

Best regards,
baolu