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Date: Thu, 14 Jul 2016 15:52:47 +0200 From: Radim Krčmář <rkrcmar@...hat.com> To: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com> Cc: joro@...tes.org, pbonzini@...hat.com, alex.williamson@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, sherry.hurwitz@....com Subject: Re: [PART2 PATCH v4 10/11] svm: Introduce AMD IOMMU avic_ga_log_notifier 2016-07-14 16:43+0700, Suravee Suthikulpanit: > On 7/13/16 21:29, Radim Krčmář wrote: >> 2016-07-13 08:20-0500, Suravee Suthikulpanit: >> > >diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c >> > >+ hash_for_each_possible(svm_vm_data_hash, ka, hnode, vm_id) { >> > >+ struct kvm *kvm = container_of(ka, struct kvm, arch); >> > >+ >> > >+ vcpu = kvm_get_vcpu_by_id(kvm, vcpu_id); >> The first result is not neccessarily the correct one. >> >> With more than active 256 VMs, there is a guaranteed collision that >> cannot be disambiguated, so VCPUs in both VMs need to be woken up. >> >> Having a 24 bit vm_id and checking that >> kvm->*.avic_id & 0xfffff == vm_id >> would help a bit to avoid useless wakeups, but the collision cannot be >> avoided. > > True. What if SVM guarantee that the VM_ID won't conflict b/w any two active > VMs? It is a nice way to avoid the bug you found in amd_iommu_update_ga() and we would send only one wakeup here as well, so it sound like the best solution.
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