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From: Marc Zyngier <marc.zyngier@arm.com>
To: Auger Eric <eric.auger@redhat.com>,
	linux-arm-kernel@lists.infradead.org,
	 kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: "Raslan, KarimAllah" <karahmed@amazon.de>,
	"Saidi, Ali" <alisaidi@amazon.com>
Subject: Re: [PATCH v2 4/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on specific commands
Date: Mon, 22 Jul 2019 11:54:25 +0100
Message-ID: <1a78d52c-7a31-8981-230b-abe85d11b8ec@arm.com> (raw)
In-Reply-To: <9ff329a3-44f2-1de3-b6cc-58ed38a63665@redhat.com>

Hi Eric,

On 01/07/2019 13:38, Auger Eric wrote:
> Hi Marc,
> 
> On 6/11/19 7:03 PM, Marc Zyngier wrote:
>> The LPI translation cache needs to be discarded when an ITS command
>> may affect the translation of an LPI (DISCARD and MAPD with V=0) or
>> the routing of an LPI to a redistributor with disabled LPIs (MOVI,
>> MOVALL).
>>
>> We decide to perform a full invalidation of the cache, irrespective
>> of the LPI that is affected. Commands are supposed to be rare enough
>> that it doesn't matter.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>>  virt/kvm/arm/vgic/vgic-its.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 9b6b66204b97..5254bb762e1b 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -733,6 +733,8 @@ static int vgic_its_cmd_handle_discard(struct kvm *kvm, struct vgic_its *its,
>>  		 * don't bother here since we clear the ITTE anyway and the
>>  		 * pending state is a property of the ITTE struct.
>>  		 */
>> +		vgic_its_invalidate_cache(kvm);
>> +
>>  		its_free_ite(kvm, ite);
>>  		return 0;
>>  	}
>> @@ -768,6 +770,8 @@ static int vgic_its_cmd_handle_movi(struct kvm *kvm, struct vgic_its *its,
>>  	ite->collection = collection;
>>  	vcpu = kvm_get_vcpu(kvm, collection->target_addr);
>>  
>> +	vgic_its_invalidate_cache(kvm);
>> +
>>  	return update_affinity(ite->irq, vcpu);
>>  }
>>  
>> @@ -996,6 +1000,8 @@ static void vgic_its_free_device(struct kvm *kvm, struct its_device *device)
>>  	list_for_each_entry_safe(ite, temp, &device->itt_head, ite_list)
>>  		its_free_ite(kvm, ite);
>>  
>> +	vgic_its_invalidate_cache(kvm);
>> +
>>  	list_del(&device->dev_list);
>>  	kfree(device);
>>  }
>> @@ -1249,6 +1255,8 @@ static int vgic_its_cmd_handle_movall(struct kvm *kvm, struct vgic_its *its,
>>  		vgic_put_irq(kvm, irq);
>>  	}
>>  
>> +	vgic_its_invalidate_cache(kvm);
> All the commands are executed with the its_lock held. Now we don't take
> it anymore on the fast cache injection path. Don't we have a window
> where the move has been applied at table level and the cache is not yet
> invalidated? Same question for vgic_its_free_device().

There is definitely a race, but that race is invisible from the guest's
perspective. The guest can only assume that the command has taken effect
once a SYNC command has been executed, and it cannot observe that the
SYNC command has been executed before we have invalidated the cache.

Does this answer your question?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-11 17:03 [PATCH v2 0/9] KVM: arm/arm64: vgic: ITS translation cache Marc Zyngier
2019-06-11 17:03 ` [PATCH v2 1/9] KVM: arm/arm64: vgic: Add LPI translation cache definition Marc Zyngier
2019-06-12  8:16   ` Julien Thierry
2019-06-12  8:49     ` Julien Thierry
2019-06-12  9:52     ` Marc Zyngier
2019-06-12 10:58       ` Julien Thierry
2019-06-12 12:28         ` Julien Thierry
2019-07-23 12:43   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 2/9] KVM: arm/arm64: vgic: Add __vgic_put_lpi_locked primitive Marc Zyngier
2019-06-11 17:03 ` [PATCH v2 3/9] KVM: arm/arm64: vgic-its: Add MSI-LPI translation cache invalidation Marc Zyngier
2019-07-23 12:39   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 4/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on specific commands Marc Zyngier
2019-07-01 12:38   ` Auger Eric
2019-07-22 10:54     ` Marc Zyngier [this message]
2019-07-23 12:25       ` Auger Eric
2019-07-23 12:43         ` Marc Zyngier
2019-07-23 12:47           ` Auger Eric
2019-07-23 12:50             ` Marc Zyngier
2019-06-11 17:03 ` [PATCH v2 5/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on disabling LPIs Marc Zyngier
2019-07-23 15:09   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 6/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on vgic teardown Marc Zyngier
2019-07-23 15:10   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 7/9] KVM: arm/arm64: vgic-its: Cache successful MSI->LPI translation Marc Zyngier
2019-06-25 11:50   ` Zenghui Yu
2019-06-25 12:31     ` Marc Zyngier
2019-06-25 16:00       ` Zenghui Yu
2019-06-26  3:54         ` Zenghui Yu
2019-06-26  7:55         ` Marc Zyngier
2019-07-23 15:21   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 8/9] KVM: arm/arm64: vgic-its: Check the LPI translation cache on MSI injection Marc Zyngier
2019-07-23 15:10   ` Auger Eric
2019-07-23 15:45     ` Marc Zyngier
2019-07-24  7:41       ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 9/9] KVM: arm/arm64: vgic-irqfd: Implement kvm_arch_set_irq_inatomic Marc Zyngier
2019-07-23 15:14   ` Auger Eric
2019-07-25  8:24     ` Marc Zyngier
2019-07-23 11:14 ` [PATCH v2 0/9] KVM: arm/arm64: vgic: ITS translation cache Andre Przywara
2019-07-25  8:50   ` Marc Zyngier
2019-07-25 10:01     ` Andre Przywara
2019-07-25 15:37       ` Marc Zyngier

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