linux-kernel - RE: [PATCH v8 04/11] iommu: Add sva iommu

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Date:   Fri, 17 Jun 2022 07:43:40 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>
CC:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Christoph Hellwig" <hch@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Vinod Koul <vkoul@...nel.org>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>, Will Deacon <will@...nel.org>
Subject: RE: [PATCH v8 04/11] iommu: Add sva iommu_domain support

> From: Baolu Lu
> Sent: Friday, June 10, 2022 3:16 PM
> >
> >> +#define __IOMMU_DOMAIN_HOST_VA	(1U << 5)  /* Host CPU virtual
> address */
> >
> > Do you mean general CPU VA? or Host CPU VA, I'm reading the latter as
> 2nd
> > stage?
> 
> Host CPU VA. In the near future, we will add another flag _GUEST_VA, so
> that the shared page table types are distiguished.

How does the kernel knows that an user page table translates guest VA?
IMHO I don't think the kernel should care about it except managing
all the aspects related to the user page table itself...

> 
> >
> >> +
> >>   /*
> >>    * This are the possible domain-types
> >>    *
> >> @@ -86,15 +89,24 @@ 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)
> >
> > Doesn't shared automatically mean CPU VA? Do we need another flag?
> 
> Yes. Shared means CPU VA, but there're many types. Besides above two, we
> also see the shared KVM/EPT.
> 

Will the two sharing scenarios share any common code? If not then
having a separate flag bit is meaningless.

It might be more straightforward to be:

#define IOMMU_DOMAIN_SVA	__IOMMU_DOMAIN_SVA
#define IOMMU_DOMAIN_KVM __IOMMU_DOMAIN_KVM
#define IOMMU_DOMAIN_USER __IOMMU_DOMAIN_USER

Thanks
Kevin