RE: [PATCH v7 11/11] iommu/vt-d: Add svm/sva invalidate function

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
> Sent: Saturday, October 26, 2019 3:03 PM
> 
> Hi again,
> 
> On 10/26/19 10:40 AM, Lu Baolu wrote:
> > Hi,
> >
> > On 10/25/19 3:27 PM, Tian, Kevin wrote:
> >>> From: Jacob Pan [mailto:jacob.jun.pan@linux.intel.com]
> >>> Sent: Friday, October 25, 2019 3:55 AM
> >>>
> >>> When Shared Virtual Address (SVA) is enabled for a guest OS via
> >>> vIOMMU, we need to provide invalidation support at IOMMU API and
> >>> driver
> >>> level. This patch adds Intel VT-d specific function to implement
> >>> iommu passdown invalidate API for shared virtual address.
> >>>
> >>> The use case is for supporting caching structure invalidation
> >>> of assigned SVM capable devices. Emulated IOMMU exposes queue
> >>> invalidation capability and passes down all descriptors from the guest
> >>> to the physical IOMMU.
> >>
> >> specifically you may clarify that only invalidations related to
> >> first-level page table is passed down, because it's guest
> >> structure being bound to the first-level. other descriptors
> >> are emulated or translated into other necessary operations.
> >>
> >>>
> >>> The assumption is that guest to host device ID mapping should be
> >>> resolved prior to calling IOMMU driver. Based on the device handle,
> >>> host IOMMU driver can replace certain fields before submit to the
> >>> invalidation queue.
> >>
> >> what is device ID? it's a bit confusing term here.
> >>
> >>>
> >>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> >>> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> >>> Signed-off-by: Liu, Yi L <yi.l.liu@linux.intel.com>
> >>> ---
> >>>   drivers/iommu/intel-iommu.c | 170
> >>> ++++++++++++++++++++++++++++++++++++++++++++
> >>>   1 file changed, 170 insertions(+)
> >>>
> >>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-
> iommu.c
> >>> index 5fab32fbc4b4..a73e76d6457a 100644
> >>> --- a/drivers/iommu/intel-iommu.c
> >>> +++ b/drivers/iommu/intel-iommu.c
> >>> @@ -5491,6 +5491,175 @@ static void
> >>> intel_iommu_aux_detach_device(struct iommu_domain *domain,
> >>>       aux_domain_remove_dev(to_dmar_domain(domain), dev);
> >>>   }
> >>>
> >>> +/*
> >>> + * 2D array for converting and sanitizing IOMMU generic TLB
> >>> granularity to
> >>> + * VT-d granularity. Invalidation is typically included in the unmap
> >>> operation
> >>> + * as a result of DMA or VFIO unmap. However, for assigned device
> where
> >>> guest
> >>> + * could own the first level page tables without being shadowed by
> >>> QEMU.
> >>> In
> >>> + * this case there is no pass down unmap to the host IOMMU as a
> >>> result of
> >>> unmap
> >>> + * in the guest. Only invalidations are trapped and passed down.
> >>> + * In all cases, only first level TLB invalidation (request with
> >>> PASID) can be
> >>> + * passed down, therefore we do not include IOTLB granularity for
> >>> request
> >>> + * without PASID (second level).
> >>> + *
> >>> + * For an example, to find the VT-d granularity encoding for IOTLB
> >>> + * type and page selective granularity within PASID:
> >>> + * X: indexed by iommu cache type
> >>> + * Y: indexed by enum iommu_inv_granularity
> >>> + * [IOMMU_CACHE_INV_TYPE_IOTLB][IOMMU_INV_GRANU_ADDR]
> >>> + *
> >>> + * Granu_map array indicates validity of the table. 1: valid, 0:
> >>> invalid
> >>> + *
> >>> + */
> >>> +const static int
> >>>
> inv_type_granu_map[IOMMU_CACHE_INV_TYPE_NR][IOMMU_INV_GRAN
> >>> U_NR] = {
> >>> +    /* PASID based IOTLB, support PASID selective and page selective */
> >>> +    {0, 1, 1},
> >>> +    /* PASID based dev TLBs, only support all PASIDs or single PASID */
> >>> +    {1, 1, 0},
> >>
> >> I forgot previous discussion. is it necessary to pass down dev TLB
> >> invalidation
> >> requests? Can it be handled by host iOMMU driver automatically?
> >
> > On host SVA, when a memory is unmapped, driver callback will invalidate
> > dev IOTLB explicitly. So I guess we need to pass down it for guest case.
> > This is also required for guest iova over 1st level usage as far as can
> > see.
> >
> 
> Sorry, I confused guest vIOVA and guest vSVA. For guest vIOVA, no device
> TLB invalidation pass down. But currently for guest vSVA, device TLB
> invalidation is passed down. Perhaps we can avoid passing down dev TLB
> flush just like what we are doing for guest IOVA.
> 

I think dev TLB is fully handled within IOMMU driver today. It doesn't
require device driver to explicit toggle. With this then we can fully
virtualize guest dev TLB invalidation request to save one syscall, since
the host is supposed to flush dev TLB when serving the earlier IOTLB
invalidation pass-down.

Thanks
Kevin