linux-kernel - Re: [PATCH 2/2] vfio: type1: conditionally check MSI remapping at irq domain level

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Date:   Thu, 2 Mar 2017 16:01:57 +0100
From:   Mian Yousaf Kaukab <yousaf.kaukab@...e.com>
To:     Auger Eric <eric.auger@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, marc.zyngier@....com,
        alex.williamson@...hat.com
Cc:     will.deacon@....com
Subject: Re: [PATCH 2/2] vfio: type1: conditionally check MSI remapping at irq
 domain level

On 03/02/2017 02:46 PM, Auger Eric wrote:
> Hi,
> 
> On 02/03/2017 13:38, Mian Yousaf Kaukab wrote:
>> On 03/02/2017 11:24 AM, Auger Eric wrote:
>>> Hi,
>>>
>>> On 02/03/2017 11:01, Mian Yousaf Kaukab wrote:
>>>> Check only if irq domains are available.
>>>>
>>>> Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@...e.com>
>>>> ---
>>>>    drivers/vfio/vfio_iommu_type1.c | 5 +++--
>>>>    1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/vfio/vfio_iommu_type1.c
>>>> b/drivers/vfio/vfio_iommu_type1.c
>>>> index bd6f293c4ebd..e3ed50e40ead 100644
>>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>>> @@ -1287,8 +1287,9 @@ static int vfio_iommu_type1_attach_group(void
>>>> *iommu_data,
>>>>        INIT_LIST_HEAD(&domain->group_list);
>>>>        list_add(&group->next, &domain->group_list);
>>>>    -    msi_remap = resv_msi ? irq_domain_check_msi_remap() :
>>>> -                iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
>>>> +    msi_remap = resv_msi && IS_ENABLED(CONFIG_IRQ_DOMAIN) ?
>>>> +            irq_domain_check_msi_remap() :
>>>> +            iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
>>> Is that patch actually needed after [PATCH 1/2] irqdomain: add empty
>>> irq_domain_check_msi_remap. irq_domain_check_msi_remap() should be
>>> defined and if you follow my suggestion, would return false. Anyway in
>>> your case resv_msi should be false.
>> I agree its an overkill if resv_msi is guaranteed to be false. What I am
>> unsure about is that, if iommu have IOMMU_RESV_MSI regions that would
>> mean that irq domains are selected in the build. If this is not
>> guaranteed, then we need to add this check.
> 
> Currently only ARM SMMUs advertise IOMMU_RESV_MSI regions. If attempting
> to do passthrough on an ARM platform not implementing IRQ_DOMAIN the
> unsafe IRQ assignment mode would need to be chosen (if
> irq_domain_check_msi_remap() returns false as discussed before). Anyway
> checking the  interrupt remapping capability on IOMMU side would report
> false as well since the capability is not exposed by ARM SMMU anymore.OK I will drop this patch. We get a warning anyway in case the 
capability is checked from the wrong place.

BR,
Yousaf