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

Paul Durrant
2023-12-04T15:02:25Z

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/20231122121822.1042-1-paul@xen.org/

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
--
2.39.2