This mini-series fixes a suspected, but technically unconfirmed, bug in
KVM related to ZONE_DEVICE pages. The suspected issue is that KVM treats
ZONE_DEVICE pages as reserved PFNs, and so doesn't put references to such
pages when dropping references via KVM's generic kvm_release_pfn_clean().
David Hildenbrand uncovered the bug during a discussion about removing
PG_reserved from ZONE_DEVICE pages, after Dan Williams pointed out[1] that
there was a bug report from Adam Borowski[2] that was likely related to
KVM's interaction with PageReserved().
Patch 1/3 contains the actual fix, patches 2/3 and 3/3 are minor cleanup
that is mostly unrelated, but dependent and prompted by the fix itself.
v2:
- Remove the kvm_is_zone_device_pfn(pfn) check from kvm_get_pfn(). It's
not entirely clear whether or not the hva_to_pfn_remapped() case is
actually broken, e.g. KVM's page fault handler is likely ok, whereas
not calling get_page() willl definitely cause breakage as KVM would
later call put_page() on the pfn/page. [Paolo]
- WARN if kvm_is_zone_device_pfn() is called without the underlying
page being pinned. This won't necessarily catch all bugs, e.g. if
the above hva_to_pfn_remapped case is indeed broken, but will
prevent completely bogus usage. [Dan]
- Remove the is_error_pfn() check from transparent_hugepage_adjust()
instead of carrying it forward into the new kvm_is_hugepage_allowed()
helper. [Paolo]
[1] http://lkml.kernel.org/r/20190919115547.GA17963@xxxxxxxxxx
[2] https://lkml.kernel.org/r/01adb4cb-6092-638c-0bab-e61322be7cf5@xxxxxxxxxx
Sean Christopherson (3):
KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
KVM: x86/mmu: Remove superfluous is_error_pfn() check from THP adjust
KVM: x86/mmu: Add helper to consolidate huge page promotion
arch/x86/kvm/mmu.c | 15 +++++++++------
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++---
3 files changed, 33 insertions(+), 9 deletions(-)
--
2.24.0
