When I implemented the parallel faults series I was mostly focused on improving the performance of 8.1+ implementations which bring us FEAT_HAFDBS. In so doing, I failed to put access faults on the read side of the MMU lock. Anyhow, this small series adds support for handling access faults in parallel, piling on top of the infrastructure from the first parallel faults series. Patch 1 is a nit I had when working on this series. Patches 2-4 improve the retry logic to avoid unnecessarily serializing and/or invalidating when an attr walker has no effect on the page tables due to a race. I added a flag to indicate whether or not a table walk takes place within a fault handler to decide whether or not an early return is necessary for EAGAIN. We could probably pile even more onto this in the future with lock contention and need_resched() detection. Patch 5 rolls over access faults to the read lock. Finally, patch 6 guards KVM's use of VTCR_EL2.HA with the corresponding kernel config option for FEAT_HAFDBS. FWIW, it is rather useful for testing access faults on systems that implement FEAT_HAFDBS. Applies to kvmarm/next. Tested on Ampere Altra w/ VTCR_EL2.HA=0 and lockdep enabled. v1 -> v2: - Don't serialize if attr walker fails due to an invalid PTE (Ricardo) - Rejig the error handling path in the table walker to suppress EAGAIN in non-fault handling paths v1: https://lore.kernel.org/kvmarm/20221129191946.1735662-1-oliver.upton@xxxxxxxxx Oliver Upton (6): KVM: arm64: Use KVM's pte type/helpers in handle_access_fault() KVM: arm64: Ignore EAGAIN for walks outside of a fault KVM: arm64: Return EAGAIN for invalid PTE in attr walker KVM: arm64: Don't serialize if the access flag isn't set KVM: arm64: Handle access faults behind the read lock KVM: arm64: Condition HW AF updates on config option arch/arm64/include/asm/kvm_pgtable.h | 8 ++++++ arch/arm64/kvm/hyp/pgtable.c | 43 ++++++++++++++++++++++++---- arch/arm64/kvm/mmu.c | 18 ++++++------ 3 files changed, 54 insertions(+), 15 deletions(-) base-commit: edf3e6d30db78cc37bb57944b2255225aa73bbe8 -- 2.39.0.rc0.267.gcb52ba06e7-goog
