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

Jason Wang
2021-01-15T04:48:43Z

On 2021/1/14 上午9:30, 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.
>
> 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)
> +{
> + 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();

This part I don't understand. Does it mean Intel IOMMU can't be used in
VM without caching mode?

Thanks

>
> 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 */
> };
>
> /*