On Sat, Feb 17, 2024, Xu Yilun wrote:
> > 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 &&
Ugh, and bad testing on my end.
