| Message ID | 20220623200029.26007-3-nicolinc@nvidia.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Simplify vfio_iommu_type1 attach/detach routine | expand |
On 2022/6/24 04:00, Nicolin Chen wrote: > From: Jason Gunthorpe <jgg@nvidia.com> > > The KVM mechanism for controlling wbinvd is based on OR of the coherency > property of all devices attached to a guest, no matter whether those > devices are attached to a single domain or multiple domains. > > On the other hand, the benefit to using separate domains was that those > devices attached to domains supporting enforced cache coherency always > mapped with the attributes necessary to provide that feature, therefore > if a non-enforced domain was dropped, the associated group removal would > re-trigger an evaluation by KVM. > > In practice however, the only known cases of such mixed domains included > an Intel IGD device behind an IOMMU lacking snoop control, where such > devices do not support hotplug, therefore this scenario lacks testing and > is not considered sufficiently relevant to support. > > After all, KVM won't take advantage of trying to push a device that could > do enforced cache coherency to a dedicated domain vs re-using an existing > domain, which is non-coherent. > > Simplify this code and eliminate the test. This removes the only logic > that needed to have a dummy domain attached prior to searching for a > matching domain and simplifies the next patches. > > It's unclear whether we want to further optimize the Intel driver to > update the domain coherency after a device is detached from it, at > least not before KVM can be verified to handle such dynamics in related > emulation paths (wbinvd, vcpu load, write_cr0, ept, etc.). In reality > we don't see an usage requiring such optimization as the only device > which imposes such non-coherency is Intel GPU which even doesn't > support hotplug/hot remove. > > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> > Reviewed-by: Kevin Tian <kevin.tian@intel.com> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com> > --- > drivers/vfio/vfio_iommu_type1.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index c13b9290e357..f4e3b423a453 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -2285,9 +2285,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data, > * testing if they're on the same bus_type. > */ > list_for_each_entry(d, &iommu->domain_list, next) { > - if (d->domain->ops == domain->domain->ops && > - d->enforce_cache_coherency == > - domain->enforce_cache_coherency) { > + if (d->domain->ops == domain->domain->ops) { > iommu_detach_group(domain->domain, group->iommu_group); > if (!iommu_attach_group(d->domain, > group->iommu_group)) { Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com> Best regards, baolu
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index c13b9290e357..f4e3b423a453 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -2285,9 +2285,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data, * testing if they're on the same bus_type. */ list_for_each_entry(d, &iommu->domain_list, next) { - if (d->domain->ops == domain->domain->ops && - d->enforce_cache_coherency == - domain->enforce_cache_coherency) { + if (d->domain->ops == domain->domain->ops) { iommu_detach_group(domain->domain, group->iommu_group); if (!iommu_attach_group(d->domain, group->iommu_group)) {