Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU

Lu Baolu
2021-01-15T00:00:03Z

Hi Leon,

On 1/14/21 9:26 PM, Leon Romanovsky wrote:
> On Thu, Jan 14, 2021 at 09:30:02AM +0800, Lu Baolu wrote:
>> Some vendor IOMMU drivers are able to declare that it is running in a VM
>> context. This is very valuable for the features that only want to be
>> supported on bare metal. Add a capability bit so that it could be used.
>
> And how is it used? Who and how will set it?

Use the existing iommu_capable(). I should add more descriptions about
who and how to use it.

>
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> drivers/iommu/intel/iommu.c | 20 ++++++++++++++++++++
>> drivers/iommu/virtio-iommu.c | 9 +++++++++
>> include/linux/iommu.h | 1 +
>> 3 files changed, 30 insertions(+)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index cb205a04fe4c..8eb022d0e8aa 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -5738,12 +5738,32 @@ static inline bool nested_mode_support(void)
>> return ret;
>> }
>>
>> +static inline bool caching_mode_enabled(void)
>> +{
>
> Kernel coding style is not in favour of inline functions in *.c files.

Yes, agreed.

Best regards,
baolu

>
>> + struct dmar_drhd_unit *drhd;
>> + struct intel_iommu *iommu;
>> + bool ret = false;
>> +
>> + rcu_read_lock();
>> + for_each_active_iommu(iommu, drhd) {
>> + if (cap_caching_mode(iommu->cap)) {
>> + ret = true;
>> + break;
>> + }
>> + }
>> + rcu_read_unlock();
>> +
>> + return ret;
>> +}
>> +
>> static bool intel_iommu_capable(enum iommu_cap cap)
>> {
>> if (cap == IOMMU_CAP_CACHE_COHERENCY)
>> return domain_update_iommu_snooping(NULL) == 1;
>> if (cap == IOMMU_CAP_INTR_REMAP)
>> return irq_remapping_enabled == 1;
>> + if (cap == IOMMU_CAP_VIOMMU)
>> + return caching_mode_enabled();
>>
>> return false;
>> }
>> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
>> index 2bfdd5734844..719793e103db 100644
>> --- a/drivers/iommu/virtio-iommu.c
>> +++ b/drivers/iommu/virtio-iommu.c
>> @@ -931,7 +931,16 @@ static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
>> return iommu_fwspec_add_ids(dev, args->args, 1);
>> }
>>
>> +static bool viommu_capable(enum iommu_cap cap)
>> +{
>> + if (cap == IOMMU_CAP_VIOMMU)
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> static struct iommu_ops viommu_ops = {
>> + .capable = viommu_capable,
>> .domain_alloc = viommu_domain_alloc,
>> .domain_free = viommu_domain_free,
>> .attach_dev = viommu_attach_dev,
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index b95a6f8db6ff..1d24be667a03 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -94,6 +94,7 @@ enum iommu_cap {
>> transactions */
>> IOMMU_CAP_INTR_REMAP, /* IOMMU supports interrupt isolation */
>> IOMMU_CAP_NOEXEC, /* IOMMU_NOEXEC flag */
>> + IOMMU_CAP_VIOMMU, /* IOMMU can declar running in a VM */
>> };
>>
>> /*
>> --
>> 2.25.1
>>