[v10,00/19] KVM: xen: update shared_info and vcpu_info handling

Message

Paul Durrant Dec. 4, 2023, 2:43 p.m. UTC

From: Paul Durrant <[e-mail]>

There are four new patches in the series over what was in version 9 [1]:

* KVM: xen: separate initialization of shared_info cache and content
* KVM: xen: (re-)initialize shared_info if guest (32/64-bit) mode is set

These deal with a missing re-initialization of shared_info if either the
guest or VMM changes the 'long_mode' flag. This was discovred in testing
when the guest wallclock reverted to the Unix epoch because the pvclock
information in the shared_info page was not in the correct place, and so
the guest read zeroes instead.

* KVM: xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()
* KVM: pfncache: check the need for invalidation under read lock first

The first of these fixes a bug discovered when compiling the kernel with
CONFIG_PROVE_RAW_LOCK_NESTING: kvm_xen_set_evtchn_fast() can be called from
the callback of a HRTIMER_MODE_ABS_HARD timer and hence be executed in
IRQ context. It should therefore not block on any lock. Thus two
occurrences of a read_lock() are converted to a read_trylock() which
kick the code down a slow-path if they fail.
The second patch removes a 'false' contention on the pfncache lock that
could result in taking that slow-path: the MMU notifier callback need only
take a pfncache read lock; it only need take a write lock if a match is
found.

Apart from these new patches...

* KVM: xen: split up kvm_xen_set_evtchn_fast()

... has been re-worked to (hopefully) improve readability and also validate
the 'correct' vcpu_info structure depending on whether the guest is in long
mode or not.

[1] https://lore.kernel.org/kvm/[e-mail]/

Paul Durrant (19):
  KVM: pfncache: Add a map helper function
  KVM: pfncache: remove unnecessary exports
  KVM: xen: mark guest pages dirty with the pfncache lock held
  KVM: pfncache: add a mark-dirty helper
  KVM: pfncache: remove KVM_GUEST_USES_PFN usage
  KVM: pfncache: stop open-coding offset_in_page()
  KVM: pfncache: include page offset in uhva and use it consistently
  KVM: pfncache: allow a cache to be activated with a fixed (userspace)
    HVA
  KVM: xen: separate initialization of shared_info cache and content
  KVM: xen: (re-)initialize shared_info if guest (32/64-bit) mode is set
  KVM: xen: allow shared_info to be mapped by fixed HVA
  KVM: xen: allow vcpu_info to be mapped by fixed HVA
  KVM: selftests / xen: map shared_info using HVA rather than GFN
  KVM: selftests / xen: re-map vcpu_info using HVA rather than GPA
  KVM: xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability
  KVM: xen: split up kvm_xen_set_evtchn_fast()
  KVM: xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast()
  KVM: pfncache: check the need for invalidation under read lock first
  KVM: xen: allow vcpu_info content to be 'safely' copied

 Documentation/virt/kvm/api.rst                |  53 ++-
 arch/x86/kvm/x86.c                            |   7 +-
 arch/x86/kvm/xen.c                            | 358 +++++++++++-------
 include/linux/kvm_host.h                      |  40 +-
 include/linux/kvm_types.h                     |   8 -
 include/uapi/linux/kvm.h                      |   9 +-
 .../selftests/kvm/x86_64/xen_shinfo_test.c    |  59 ++-
 virt/kvm/pfncache.c                           | 185 ++++-----
 8 files changed, 461 insertions(+), 258 deletions(-)


base-commit: 1ab097653e4dd8d23272d028a61352c23486fd4a