Re: [PATCH RFC 02/11] iommu: Add iommu_domain type for SVA

[Lu Baolu]

On 2022/3/21 19:47, Jason Gunthorpe wrote:
> On Sun, Mar 20, 2022 at 02:40:21PM +0800, Lu Baolu wrote:
> > Add a new iommu domain type IOMMU_DOMAIN_SVA to represent an I/O page
> > table which is shared from CPU host VA. Add a sva_cookie field in the
> > iommu_domain structure to save the mm_struct which represent the CPU
> > memory page table.
> >
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >   include/linux/iommu.h | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 36f43af0af53..3e179b853380 100644
> > +++ b/include/linux/iommu.h
> > @@ -64,6 +64,9 @@ struct iommu_domain_geometry {
> >   #define __IOMMU_DOMAIN_PT	(1U << 2)  /* Domain is identity mapped   */
> >   #define __IOMMU_DOMAIN_DMA_FQ	(1U << 3)  /* DMA-API uses flush queue    */
> >   
> > +#define __IOMMU_DOMAIN_SHARED	(1U << 4)  /* Page table shared from CPU  */
> > +#define __IOMMU_DOMAIN_HOST_VA	(1U << 5)  /* Host CPU virtual address */
> > +
> >   /*
> >    * This are the possible domain-types
> >    *
> > @@ -86,6 +89,8 @@ struct iommu_domain_geometry {
> >   #define IOMMU_DOMAIN_DMA_FQ	(__IOMMU_DOMAIN_PAGING |	\
> >   				 __IOMMU_DOMAIN_DMA_API |	\
> >   				 __IOMMU_DOMAIN_DMA_FQ)
> > +#define IOMMU_DOMAIN_SVA	(__IOMMU_DOMAIN_SHARED |	\
> > +				 __IOMMU_DOMAIN_HOST_VA)
>
> Is there any use for this in the core code? I feel like flags should
> only be created if the core code needs to test them in some way.

flags are some attributes of the domain and the combination of multiple
flags forms a domain type.

> > @@ -95,6 +100,7 @@ struct iommu_domain {
> >   	void *handler_token;
> >   	struct iommu_domain_geometry geometry;
> >   	struct iommu_dma_cookie *iova_cookie;
> > +	struct mm_struct *sva_cookie;
>
> Don't call a mm_struct a cookie please

Sure.

> And why do we need this in core code?

Need to connect an SVA domain with mm.

Best regards,
baolu