> static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
> unsigned int access)
> {
> + struct kvm_memory_slot *slot = fault->slot;
> int ret;
>
> fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq;
> smp_rmb();
>
> + /*
> + * Check for a relevant mmu_notifier invalidation event before getting
> + * the pfn from the primary MMU, and before acquiring mmu_lock.
> + *
> + * For mmu_lock, if there is an in-progress invalidation and the kernel
> + * allows preemption, the invalidation task may drop mmu_lock and yield
> + * in response to mmu_lock being contended, which is *very* counter-
> + * productive as this vCPU can't actually make forward progress until
> + * the invalidation completes.
> + *
> + * Retrying now can also avoid unnessary lock contention in the primary
> + * MMU, as the primary MMU doesn't necessarily hold a single lock for
> + * the duration of the invalidation, i.e. faulting in a conflicting pfn
> + * can cause the invalidation to take longer by holding locks that are
> + * needed to complete the invalidation.
> + *
> + * Do the pre-check even for non-preemtible kernels, i.e. even if KVM
> + * will never yield mmu_lock in response to contention, as this vCPU is
> + * *guaranteed* to need to retry, i.e. waiting until mmu_lock is held
> + * to detect retry guarantees the worst case latency for the vCPU.
> + */
> + if (!slot &&
typo? if (slot &&
Thanks,
Yilun
> + mmu_invalidate_retry_gfn_unsafe(vcpu->kvm, fault->mmu_seq, fault->gfn))
> + return RET_PF_RETRY;
> +
> ret = __kvm_faultin_pfn(vcpu, fault);
> if (ret != RET_PF_CONTINUE)
> return ret;
