From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PART2 PATCH v4 10/11] svm: Introduce AMD IOMMU
 avic_ga_log_notifier
Date: Thu, 14 Jul 2016 15:52:47 +0200
Message-ID: <20160714135247.GB20689@potion>
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Cc: joro@8bytes.org, pbonzini@redhat.com, alex.williamson@redhat.com,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
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To: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
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2016-07-14 16:43+0700, Suravee Suthikulpanit:
> On 7/13/16 21:29, Radim Kr=C4=8Dm=C3=A1=C5=99 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 =3D container_of(ka, struct kvm, arch);
>> > >+
>> > >+		vcpu =3D kvm_get_vcpu_by_id(kvm, vcpu_id);
>> The first result is not neccessarily the correct one.
>>=20
>> 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.
>>=20
>> Having a 24 bit vm_id and checking that
>>    kvm->*.avic_id & 0xfffff =3D=3D vm_id
>> would help a bit to avoid useless wakeups, but the collision cannot =
be
>> avoided.
>=20
> 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() an=
d
we would send only one wakeup here as well, so it sound like the best
solution.