On 5/22/26 10:44, Duan, Zhenzhong wrote:
-----Original Message-----
From: Liu, Yi L <[email protected]>
Subject: Re: [PATCH v5 09/15] intel_iommu_accel: Handle PASID entry addition for
pc_inv_dsc request
On 5/9/26 12:08, Zhenzhong Duan wrote:
Structure VTDAddressSpace includes some elements suitable for emulated
device and passthrough device without PASID, e.g., address space,
different memory regions, etc, it is also protected by vtd iommu lock,
all these are useless and become a burden for passthrough device with
PASID.
When there are lots of PASIDs used in one device, the AS and MRs are
all registered to memory core and impact the whole system performance.
So instead of using VTDAddressSpace to cache pasid entry for each pasid
of a passthrough device, we define a light weight structure
VTDAccelPASIDCacheEntry with only necessary elements for each pasid. We
will use this struct as a parameter to conduct binding/unbinding to
nested hwpt and to record the current bound nested hwpt. It's also
designed to support IOMMU_NO_PASID.
VTDAccelPASIDCacheEntry is designed to only be used in intel_iommu_accel.c,
similarly VTDPASIDCacheEntry should only be used in hw/i386/intel_iommu.c
When guest creates new PASID entries, QEMU will capture the pc_inv_dsc
(pasid cache invalidation) request, walk through each pasid in each
passthrough device for valid pasid entries, create a new
VTDAccelPASIDCacheEntry if not existing yet.
IOMMU_NO_PASID of passthrough device still need to register MRs in case
guest does not operate in scalable mode. So for IOMMU_NO_PASID, we have
both VTDAPASIDCacheEntry and VTDAccelPASIDCacheEntry.
The implementation LGTM. But I got a question to ask here.
VTDAPASIDCacheEntry is cached in VTDAddressSpace, while
VTDAccelPASIDCacheEntry is cached in VTDHostIOMMUDevice. A natural
question is why usingVTDHostIOMMUDevice instead of VTDAddressSpace. I
think it might be valuable to mark the reason of this choice. This
would help maintaining it in future as we might forgot the reason. :)
Hmm, you mean why not putting VTDAccelPASIDCacheEntry list in VTDAddressSpace?
There is explanation above, paste here:
VTDAccelPASIDCacheEntry is designed to only be used in intel_iommu_accel.c,
similarly VTDPASIDCacheEntry should only be used in hw/i386/intel_iommu.c
hmmm. code isolation is a good reason. Is there any other reason?
