Re: [PATCH v5 00/12] KVM: x86/xen: Add in-kernel Xen event channel delivery

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On 11/21/21 13:54, David Woodhouse wrote:
Introduce the basic concept of 2 level event channels for kernel delivery,
which is just a simple matter of a few test_and_set_bit calls on a mapped
shared info page.

This can be used for routing MSI of passthrough devices to PIRQ event
channels in a Xen guest, and we can build on it for delivering IPIs and
timers directly from the kernel too.

v1: Use kvm_map_gfn() although I didn't quite see how it works.

v2: Avoid kvm_map_gfn() and implement a safe mapping with invalidation
     support for myself.

v3: Reinvent gfn_to_pfn_cache with sane invalidation semantics, for my
     use case as well as nesting.

v4: Rework dirty handling, as it became apparently that we need an active
     vCPU context to mark pages dirty so it can't be done from the MMU
     notifier duing the invalidation; it has to happen on unmap.

v5: Fix sparse warnings reported by kernel test robot<lkp@xxxxxxxxx>.

     Fix revalidation when memslots change but the resulting HVA stays
     the same. We can use the same kernel mapping in that case, if the
     HVA → PFN translation was valid before. So that probably means we
     shouldn't unmap the "old_hva". Augment the test case to exercise
     that one too.

     Include the fix for the dirty ring vs. Xen shinfo oops reported
     by butt3rflyh4ck<butterflyhuangxx@xxxxxxxxx>.


As in the previous two rounds, the last patch (this time patch 12) is
included as illustration of how we*might*  use this for fixing the UAF
bugs in nesting, but isn't intended to be applied as-is. Patches 1-11 are.

Queued 1-7, will be on kvm/next tomorrow though.

Paolo



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