[PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Eric Auger]

Saving/restoring an unmapped collection is a valid scenario. For
example this happens if a MAPTI command was sent, featuring an
unmapped collection. At the moment the CTE fails to be restored.
Only compare against the number of online vcpus if the rdist
base is set.

Cc: stable@vger.kernel.org # v4.11+
Fixes: ea1ad53e1e31a ("KVM: arm64: vgic-its: Collection table save/restore")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 virt/kvm/arm/vgic/vgic-its.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 98c7360d9fb7..17920d1b350a 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -2475,7 +2475,8 @@ static int vgic_its_restore_cte(struct vgic_its *its, gpa_t gpa, int esz)
 	target_addr = (u32)(val >> KVM_ITS_CTE_RDBASE_SHIFT);
 	coll_id = val & KVM_ITS_CTE_ICID_MASK;
 
-	if (target_addr >= atomic_read(&kvm->online_vcpus))
+	if (target_addr != COLLECTION_NOT_MAPPED &&
+	    target_addr >= atomic_read(&kvm->online_vcpus))
 		return -EINVAL;
 
 	collection = find_collection(its, coll_id);
-- 
2.20.1

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Re: [PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Marc Zyngier]

Hi Eric,

On 2019-12-13 09:42, Eric Auger wrote:
> Saving/restoring an unmapped collection is a valid scenario. For
> example this happens if a MAPTI command was sent, featuring an
> unmapped collection. At the moment the CTE fails to be restored.
> Only compare against the number of online vcpus if the rdist
> base is set.
>
> Cc: stable@vger.kernel.org # v4.11+
> Fixes: ea1ad53e1e31a ("KVM: arm64: vgic-its: Collection table 
> save/restore")
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c 
> b/virt/kvm/arm/vgic/vgic-its.c
> index 98c7360d9fb7..17920d1b350a 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -2475,7 +2475,8 @@ static int vgic_its_restore_cte(struct vgic_its
> *its, gpa_t gpa, int esz)
>  	target_addr = (u32)(val >> KVM_ITS_CTE_RDBASE_SHIFT);
>  	coll_id = val & KVM_ITS_CTE_ICID_MASK;
>
> -	if (target_addr >= atomic_read(&kvm->online_vcpus))
> +	if (target_addr != COLLECTION_NOT_MAPPED &&
> +	    target_addr >= atomic_read(&kvm->online_vcpus))
>  		return -EINVAL;
>
>  	collection = find_collection(its, coll_id);

Looks good to me. Out of curiosity, how was this spotted?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...
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Re: [PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Auger Eric]

Hi Marc,

On 12/13/19 11:43 AM, Marc Zyngier wrote:
> Hi Eric,
> 
> On 2019-12-13 09:42, Eric Auger wrote:
>> Saving/restoring an unmapped collection is a valid scenario. For
>> example this happens if a MAPTI command was sent, featuring an
>> unmapped collection. At the moment the CTE fails to be restored.
>> Only compare against the number of online vcpus if the rdist
>> base is set.
>>
>> Cc: stable@vger.kernel.org # v4.11+
>> Fixes: ea1ad53e1e31a ("KVM: arm64: vgic-its: Collection table
>> save/restore")
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> ---
>>  virt/kvm/arm/vgic/vgic-its.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 98c7360d9fb7..17920d1b350a 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -2475,7 +2475,8 @@ static int vgic_its_restore_cte(struct vgic_its
>> *its, gpa_t gpa, int esz)
>>      target_addr = (u32)(val >> KVM_ITS_CTE_RDBASE_SHIFT);
>>      coll_id = val & KVM_ITS_CTE_ICID_MASK;
>>
>> -    if (target_addr >= atomic_read(&kvm->online_vcpus))
>> +    if (target_addr != COLLECTION_NOT_MAPPED &&
>> +        target_addr >= atomic_read(&kvm->online_vcpus))
>>          return -EINVAL;
>>
>>      collection = find_collection(its, coll_id);
> 
> Looks good to me. Out of curiosity, how was this spotted?

I am currently writing some kvm-unit-tests to better test ITS and its
migration.

Thanks

Eric
> 
> Thanks,
> 
>         M.

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Re: [PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Zenghui Yu]

Hi Eric,

On 2019/12/13 17:42, Eric Auger wrote:
> Saving/restoring an unmapped collection is a valid scenario. For
> example this happens if a MAPTI command was sent, featuring an
> unmapped collection. At the moment the CTE fails to be restored.
> Only compare against the number of online vcpus if the rdist
> base is set.

Have you actually seen a problem and this patch fixed it? To be honest,
I'm surprised to find that we can map a LPI to an unmapped collection ;)
(and prevent it to be delivered to vcpu with an INT_UNMAPPED_INTERRUPT
error, until someone had actually mapped the collection).
After a quick glance of spec (MAPTI), just as you said, this is valid.

If Marc has no objection to this fix, please add

Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>


Thanks,
Zenghui

> 
> Cc: stable@vger.kernel.org # v4.11+
> Fixes: ea1ad53e1e31a ("KVM: arm64: vgic-its: Collection table save/restore")
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>   virt/kvm/arm/vgic/vgic-its.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 98c7360d9fb7..17920d1b350a 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -2475,7 +2475,8 @@ static int vgic_its_restore_cte(struct vgic_its *its, gpa_t gpa, int esz)
>   	target_addr = (u32)(val >> KVM_ITS_CTE_RDBASE_SHIFT);
>   	coll_id = val & KVM_ITS_CTE_ICID_MASK;
>   
> -	if (target_addr >= atomic_read(&kvm->online_vcpus))
> +	if (target_addr != COLLECTION_NOT_MAPPED &&
> +	    target_addr >= atomic_read(&kvm->online_vcpus))
>   		return -EINVAL;
>   
>   	collection = find_collection(its, coll_id);
> 

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Re: [PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Auger Eric]

Hi Zenghui,

On 12/13/19 11:53 AM, Zenghui Yu wrote:
> Hi Eric,
> 
> On 2019/12/13 17:42, Eric Auger wrote:
>> Saving/restoring an unmapped collection is a valid scenario. For
>> example this happens if a MAPTI command was sent, featuring an
>> unmapped collection. At the moment the CTE fails to be restored.
>> Only compare against the number of online vcpus if the rdist
>> base is set.
> 
> Have you actually seen a problem and this patch fixed it?

It is not with a linux guest but with kvm-unit-test.

 To be honest,
> I'm surprised to find that we can map a LPI to an unmapped collection ;)
> (and prevent it to be delivered to vcpu with an INT_UNMAPPED_INTERRUPT
> error, until someone had actually mapped the collection).
> After a quick glance of spec (MAPTI), just as you said, this is valid.
> 
> If Marc has no objection to this fix, please add
> 
> Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Thank you for the review.

Eric
> 
> 
> Thanks,
> Zenghui
> 
>>
>> Cc: stable@vger.kernel.org # v4.11+
>> Fixes: ea1ad53e1e31a ("KVM: arm64: vgic-its: Collection table
>> save/restore")
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> ---
>>   virt/kvm/arm/vgic/vgic-its.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 98c7360d9fb7..17920d1b350a 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -2475,7 +2475,8 @@ static int vgic_its_restore_cte(struct vgic_its
>> *its, gpa_t gpa, int esz)
>>       target_addr = (u32)(val >> KVM_ITS_CTE_RDBASE_SHIFT);
>>       coll_id = val & KVM_ITS_CTE_ICID_MASK;
>>   -    if (target_addr >= atomic_read(&kvm->online_vcpus))
>> +    if (target_addr != COLLECTION_NOT_MAPPED &&
>> +        target_addr >= atomic_read(&kvm->online_vcpus))
>>           return -EINVAL;
>>         collection = find_collection(its, coll_id);
>>
> 

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Re: [PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Marc Zyngier]

Hi Zenghui,

On 2019-12-13 10:53, Zenghui Yu wrote:
> Hi Eric,
>
> On 2019/12/13 17:42, Eric Auger wrote:
>> Saving/restoring an unmapped collection is a valid scenario. For
>> example this happens if a MAPTI command was sent, featuring an
>> unmapped collection. At the moment the CTE fails to be restored.
>> Only compare against the number of online vcpus if the rdist
>> base is set.
>
> Have you actually seen a problem and this patch fixed it? To be 
> honest,
> I'm surprised to find that we can map a LPI to an unmapped collection 
> ;)
> (and prevent it to be delivered to vcpu with an 
> INT_UNMAPPED_INTERRUPT
> error, until someone had actually mapped the collection).
> After a quick glance of spec (MAPTI), just as you said, this is 
> valid.

Yes, this is one of the (many) odd bits in the architecture. And there 
is
a bizarre wording in the MAPC description when V=0:

"Behavior is unpredictable if there are interrupts that are mapped to 
the
specified collection, with the restriction that further translation 
requests
from that device are ignored."

It is really odd that:

- it is unpredictable to unmap the collection with mapped interrupts,
   but mapping interrupts to an unmapped collection is fine

- the notion of "interrupts from that device" doesn't match any of the
   MAPC parameters

Do you hate the GIC already? ;-)

> If Marc has no objection to this fix, please add
>
> Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>

Thanks for that, I've applied it to the patch and will push out
the update as soon as ra.kernel.org is reachable again.

         M.
-- 
Jazz is not dead. It just smells funny...
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Re: [PATCH] KVM: arm/arm64: vgic-its: Fix restoration of unmapped collections

[Zenghui Yu]

Hi Marc,

On 2019/12/13 19:28, Marc Zyngier wrote:
> Hi Zenghui,
> 
> On 2019-12-13 10:53, Zenghui Yu wrote:
>> Hi Eric,
>>
>> On 2019/12/13 17:42, Eric Auger wrote:
>>> Saving/restoring an unmapped collection is a valid scenario. For
>>> example this happens if a MAPTI command was sent, featuring an
>>> unmapped collection. At the moment the CTE fails to be restored.
>>> Only compare against the number of online vcpus if the rdist
>>> base is set.
>>
>> Have you actually seen a problem and this patch fixed it? To be honest,
>> I'm surprised to find that we can map a LPI to an unmapped collection ;)
>> (and prevent it to be delivered to vcpu with an INT_UNMAPPED_INTERRUPT
>> error, until someone had actually mapped the collection).
>> After a quick glance of spec (MAPTI), just as you said, this is valid.
> 
> Yes, this is one of the (many) odd bits in the architecture. And there is
> a bizarre wording in the MAPC description when V=0:
> 
> "Behavior is unpredictable if there are interrupts that are mapped to the
> specified collection, with the restriction that further translation 
> requests
> from that device are ignored."
> 
> It is really odd that:
> 
> - it is unpredictable to unmap the collection with mapped interrupts,
>    but mapping interrupts to an unmapped collection is fine

Yes, looks odd... Without Eric's patch, I won't even notice it.

I guess that unmapping the collection with mapped interrupts will make
it difficult for Hardware to manage those interrupts' internal states,
but only a guess.

> - the notion of "interrupts from that device" doesn't match any of the
>    MAPC parameters

Looks like a writing mistake, a better statement *might be*
"further translation requests targeting that ICID are ignored"?

> Do you hate the GIC already? ;-)

Not yet! (I'd like to continue being messed with GIC and see when I
will hate it :)

> 
>> If Marc has no objection to this fix, please add
>>
>> Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
> 
> Thanks for that, I've applied it to the patch and will push out
> the update as soon as ra.kernel.org is reachable again.

Thanks,
Zenghui

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