Messages in this thread | | | From | Sean Christopherson <> | Subject | [PATCH v2 0/3] KVM: MMU: Fix a refcount bug with ZONE_DEVICE pages | Date | Mon, 11 Nov 2019 14:12:26 -0800 |
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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@angband.pl [2] https://lkml.kernel.org/r/01adb4cb-6092-638c-0bab-e61322be7cf5@redhat.com
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
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