Re: [PATCH 1/1] iommu/vt-d: Avoid WARNING in sva unbind path

[Baolu Lu]

On 5/20/26 21:12, Yi Liu wrote:
> On 5/19/26 13:29, Lu Baolu wrote:
> > The Intel IOMMU driver allows SVA on devices even if they do not support
> > PCI/PRI. Commit 39c20c4e83b9 ("iommu/vt-d: Only handle IOPF for SVA when
> > PRI is supported") modified the SVA bind path to allow this configuration
> > by skipping IOPF enablement when PRI is missing. However, it failed to
> > update the unbind path.
> >
> > This creates an imbalance: the unbind path attempts to disable IOPF for
> > a device that never had it enabled, triggering a WARNING in
> > intel_iommu_disable_iopf():
> >
> >   WARNING: drivers/iommu/intel/iommu.c:3475 at 
> > intel_iommu_disable_iopf+0x4f/0x90d
> >   Call Trace:
> >    <TASK>
> >    blocking_domain_set_dev_pasid+0x50/0x70
> >    iommu_detach_device_pasid+0x89/0xc0
> >    iommu_sva_unbind_device+0x73/0x150
> >    xe_vm_close_and_put+0x4d2/0x1200 [xe]
> >
> > Fix this by bypassing IOPF operations for SVA domains on non-PRI hardware
> > in both the bind and unbind paths.
> >
> > Fixes: 39c20c4e83b9 ("iommu/vt-d: Only handle IOPF for SVA when PRI is 
> > supported")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reported-by: Nareshkumar Gollakoti <naresh.kumar.g@xxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.h | 11 +++++++++++
> >   drivers/iommu/intel/svm.c   | 12 ++++--------
> >   2 files changed, 15 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> > index ef145560aa98..775f1c4ae346 100644
> > --- a/drivers/iommu/intel/iommu.h
> > +++ b/drivers/iommu/intel/iommu.h
> > @@ -1254,18 +1254,29 @@ void intel_iommu_disable_iopf(struct device 
> > *dev);
> >   static inline int iopf_for_domain_set(struct iommu_domain *domain,
> >                         struct device *dev)
> >   {
> > +    struct device_domain_info *info = dev_iommu_priv_get(dev);
> > +
> >       if (!domain || !domain->iopf_handler)
> >           return 0;
> > +    /* SVA with non-IOMMU/PRI IOPF handling is allowed. */
> > +    if (domain->type == IOMMU_DOMAIN_SVA && !info->pri_supported)
> > +        return 0;
> > +
>
> Looked into the history a bit, and this story begins with commit
> a86fb7717320 ("iommu/vt-d: Allow SVA with device-specific IOPF"). This
> commit enabled devices that support their own IOPF mechanism to use SVA
> even when the platform IOMMU doesn't support IOPF.
>
> However, SVA isn't the only fault-capable domain type. Other fault-capable
> domain types (e.g., paging domains) should also be able to leverage
> device-specific IOPF capabilities.
>
> My question is: can we drop the domain type check to support other types
> of fault-capable domains that rely on device-specific IOPF?

The Intel IOMMU driver treats the SVA case as a special case. It allows
an SVA domain with a registered iopf_handler to attach to a device for
SVA functionality. Broadly speaking, it would be better to handle this
in the IOMMU core — for example, by preventing the attachment of a
fault-capable domain to a device that lacks IOMMU-backed page fault
capabilities.

Thanks,
baolu