[v7,6/7] iommu/arm-smmu: do not advertise IOMMU_CAP_INTR_REMAP

Message ID 1461086687-2658-7-git-send-email-eric.auger@linaro.org
State Superseded
Headers show

Commit Message

Auger Eric April 19, 2016, 5:24 p.m.
Do not advertise IOMMU_CAP_INTR_REMAP for arm-smmu(-v3). Indeed the
irq_remapping capability is abstracted on irqchip side for ARM as
opposed to Intel IOMMU featuring IRQ remapping HW.

So to check IRQ remapping capability, the msi domain needs to be
checked instead.

This commit needs to be applied after "vfio/type1: also check IRQ
remapping capability at msi domain" else the legacy interrupt
assignment gets broken with arm-smmu.

Signed-off-by: Eric Auger <eric.auger@linaro.org>

---
 drivers/iommu/arm-smmu-v3.c | 3 ++-
 drivers/iommu/arm-smmu.c    | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

-- 
1.9.1

Comments

Auger Eric April 22, 2016, 11:39 a.m. | #1
Hi Robin,
On 04/22/2016 01:16 PM, Robin Murphy wrote:
> Hi Eric, Alex,

> 

> On 19/04/16 18:24, Eric Auger wrote:

>> Do not advertise IOMMU_CAP_INTR_REMAP for arm-smmu(-v3). Indeed the

>> irq_remapping capability is abstracted on irqchip side for ARM as

>> opposed to Intel IOMMU featuring IRQ remapping HW.

>>

>> So to check IRQ remapping capability, the msi domain needs to be

>> checked instead.

>>

>> This commit needs to be applied after "vfio/type1: also check IRQ

>> remapping capability at msi domain" else the legacy interrupt

>> assignment gets broken with arm-smmu.

> 

> Hmm, that smells of papering over a different problem. I may have missed

> it, but I don't see anything changing legacy interrupt behaviour in this

> series - are legacy INTx (or platform) interrupts intrinsically safe

> because they're physically wired, or intrinsically unsafe because they

> could be shared?


I think it is safe. With legacy/platform interrupts we have:
vfio pci driver physical IRQ handler signals an irqfd.
upon this irqfd signaling KVM injects a virtual IRQ.

So the assigned device does not have any way to trigger a storm of
interrupts on the host, as opposed to with MSI.

Does it make sense to you?

Best Regards

Eric

 If it's the latter then I don't see how the IOMMU or
> MSI controller changes anything in that respect, and if it's the former

> then surely we should support that right now without the SMMU having to

> lie about MSI isolation? I started looking into it but I'm a bit lost...

> 

> Robin.

> 

>> Signed-off-by: Eric Auger <eric.auger@linaro.org>

>> ---

>>   drivers/iommu/arm-smmu-v3.c | 3 ++-

>>   drivers/iommu/arm-smmu.c    | 3 ++-

>>   2 files changed, 4 insertions(+), 2 deletions(-)

>>

>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c

>> index afd0dac..1d0106c 100644

>> --- a/drivers/iommu/arm-smmu-v3.c

>> +++ b/drivers/iommu/arm-smmu-v3.c

>> @@ -1386,7 +1386,8 @@ static bool arm_smmu_capable(enum iommu_cap cap)

>>       case IOMMU_CAP_CACHE_COHERENCY:

>>           return true;

>>       case IOMMU_CAP_INTR_REMAP:

>> -        return true; /* MSIs are just memory writes */

>> +        /* interrupt translation handled at MSI controller level */

>> +        return false;

>>       case IOMMU_CAP_NOEXEC:

>>           return true;

>>       default:

>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c

>> index 492339f..6232b2a 100644

>> --- a/drivers/iommu/arm-smmu.c

>> +++ b/drivers/iommu/arm-smmu.c

>> @@ -1312,7 +1312,8 @@ static bool arm_smmu_capable(enum iommu_cap cap)

>>            */

>>           return true;

>>       case IOMMU_CAP_INTR_REMAP:

>> -        return true; /* MSIs are just memory writes */

>> +        /* interrupt translation handled at MSI controller level */

>> +        return false;

>>       case IOMMU_CAP_NOEXEC:

>>           return true;

>>       default:

>>

>

Patch

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index afd0dac..1d0106c 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -1386,7 +1386,8 @@  static bool arm_smmu_capable(enum iommu_cap cap)
 	case IOMMU_CAP_CACHE_COHERENCY:
 		return true;
 	case IOMMU_CAP_INTR_REMAP:
-		return true; /* MSIs are just memory writes */
+		/* interrupt translation handled at MSI controller level */
+		return false;
 	case IOMMU_CAP_NOEXEC:
 		return true;
 	default:
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 492339f..6232b2a 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1312,7 +1312,8 @@  static bool arm_smmu_capable(enum iommu_cap cap)
 		 */
 		return true;
 	case IOMMU_CAP_INTR_REMAP:
-		return true; /* MSIs are just memory writes */
+		/* interrupt translation handled at MSI controller level */
+		return false;
 	case IOMMU_CAP_NOEXEC:
 		return true;
 	default: