Re: stable backports for "KVM: x86: Fix shadow paging use-after-free due to unexpected GFN"

[Nathan Gao <zcgao@amazon.com>]

Thanks Paolo! I tested these in the context of Amazon Linux, carrying the
series as a downstream patch set on top of our 5.10 and 5.15 trees, as
follows.

Test setup
- Trees: Amazon Linux 5.10 and 5.15, with the backports applied as
  downstream patches. (For 5.10, applied a83e50d86^..d3d0e6688; for 5.15,
  applied 4db658c99^..1ab8cd246)
- For each tree we ran with EPT enabled and disabled, i.e.
    sudo rmmod kvm_intel && sudo modprobe kvm_intel ept=0
  and confirmed via /sys/module/kvm_intel/parameters/ept.
- Tested with AWS EC2 c5.metal.

Tests
- KVM selftests: make -C tools/testing/selftests/kvm run_tests
- kvm-unit-tests: https://www.linux-kvm.org/page/KVM-unit-tests

For each (tree x EPT setting) we collected results before and after
applying the backport and compared them.

Results
- No regressions. On both 5.10 and 5.15, and with EPT on and off, the
  test outcomes are the same before and after the backport.
- kvm-unit-tests output was identical before vs. after.
- The KVM selftest verdicts (ok/not ok) were identical before vs. after.
  The handful of failing tests are pre-existing on our baseline and
  unrelated to the MMU change (e.g. debug_regs, vmx_pmu_msrs_test, a
  memslot_perf_test timeout, etc.).

So from these tests, the backport looks good. Please let me know if
there are any other tests I can help with. 

Tested-by: Nathan Gao <zcgao@amazon.com>

Thanks,
Nathan Gao