Re: [PATCH V10 08/11] iommu/vt-d: Add svm/sva invalidate function

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Tue, 31 Mar 2020 02:49:21 +0000
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Auger Eric <eric.auger@redhat.com>
> > Sent: Sunday, March 29, 2020 11:34 PM
> > 
> > Hi,
> > 
> > On 3/28/20 11:01 AM, Tian, Kevin wrote:  
> > >> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > >> Sent: Saturday, March 21, 2020 7:28 AM
> > >>
> > >> When Shared Virtual Address (SVA) is enabled for a guest OS via
> > >> vIOMMU, we need to provide invalidation support at IOMMU API
> > >> and  
> > driver  
> > >> level. This patch adds Intel VT-d specific function to implement
> > >> iommu passdown invalidate API for shared virtual address.
> > >>
> > >> The use case is for supporting caching structure invalidation
> > >> of assigned SVM capable devices. Emulated IOMMU exposes queue  
>  [...]  
>  [...]  
> > to  
> > >> + * VT-d granularity. Invalidation is typically included in the
> > >> unmap  
> > operation  
> > >> + * as a result of DMA or VFIO unmap. However, for assigned
> > >> devices  
> > guest  
> > >> + * owns the first level page tables. Invalidations of
> > >> translation caches in  
> > the  
>  [...]  
>  [...]  
>  [...]  
> > inv_type_granu_map[IOMMU_CACHE_INV_TYPE_NR][IOMMU_INV_GRANU_  
> > >> NR] = {
> > >> +	/*
> > >> +	 * PASID based IOTLB invalidation: PASID selective (per
> > >> PASID),
> > >> +	 * page selective (address granularity)
> > >> +	 */
> > >> +	{0, 1, 1},
> > >> +	/* PASID based dev TLBs, only support all PASIDs or
> > >> single PASID */
> > >> +	{1, 1, 0},  
> > >
> > > Is this combination correct? when single PASID is being
> > > specified, it is essentially a page-selective invalidation since
> > > you need provide Address and Size.  
> > Isn't it the same when G=1? Still the addr/size is used. Doesn't
> > it  
> 
> I thought addr/size is not used when G=1, but it might be wrong. I'm
> checking with our vt-d spec owner.
> 

> > correspond to IOMMU_INV_GRANU_ADDR with
> > IOMMU_INV_ADDR_FLAGS_PASID flag
> > unset?
> > 
> > so {0, 0, 1}?  
> 
I am not sure I got your logic. The three fields correspond to 
	IOMMU_INV_GRANU_DOMAIN,	/* domain-selective invalidation */
	IOMMU_INV_GRANU_PASID,	/* PASID-selective invalidation */
	IOMMU_INV_GRANU_ADDR,	/* page-selective invalidation *

For devTLB, we use domain as global since there is no domain. Then I
came up with {1, 1, 0}, which means we could have global and pasid
granu invalidation for PASID based devTLB.

If the caller also provide addr and S bit, the flush routine will put
that into QI descriptor. I know this is a little odd, but from the
granu translation p.o.v. VT-d spec has no G bit for page selective
invalidation.

> I have one more open:
> 
> How does userspace know which invalidation type/gran is supported?
> I didn't see such capability reporting in Yi's VFIO vSVA patch set.
> Do we want the user/kernel assume the same capability set if they are 
> architectural? However the kernel could also do some optimization
> e.g. hide devtlb invalidation capability given that the kernel
> already invalidate devtlb automatically when serving iotlb
> invalidation...
> 
In general, we are trending to use VFIO capability chain to expose iommu
capabilities.

But for architectural features such as type/granu, we have to assume
the same capability between host & guest. Granu and types are not
enumerated on the host IOMMU either.

For devTLB optimization, I agree we need to expose a capability to
the guest stating that implicit devtlb invalidation is supported.
Otherwise, if Linux guest runs on other OSes may not support implicit
devtlb invalidation.

Right Yi?

> Thanks
> Kevin
> 
> > 
> > Thanks
> > 
> > Eric
> >   
> > >  
> > >> +	/* PASID cache */  
> > >
> > > PASID cache is fully managed by the host. Guest PASID cache
> > > invalidation is interpreted by vIOMMU for bind and unbind
> > > operations. I don't think we should accept any PASID cache
> > > invalidation from userspace or guest. 
>  [...]  
> > inv_type_granu_table[IOMMU_CACHE_INV_TYPE_NR][IOMMU_INV_GRANU  
>  [...]  
> > >
> > > btw do we really need both map and table here? Can't we just
> > > use one table with unsupported granularity marked as a special
> > > value?
> > >  
>  [...]  
> > >
> > > -ENOTSUPP?
> > >  
>  [...]  
> > >
> > > granularity == IOMMU_INV_GRANU_ADDR? otherwise it's unclear
> > > why IOMMU_INV_GRANU_DOMAIN also needs size check.
> > >  
>  [...]  
> > >>> addr_info.addr),  
>  [...]  
>  [...]  
> > >> +			if (info->ats_enabled) {
> > >> +				qi_flush_dev_iotlb_pasid(iommu,
> > >> sid, info-  
> > >>> pfsid,  
>  [...]  
> > >>> pfsid,  
> > >> +
> > >> inv_info->addr_info.pasid, info->ats_qdep,
> > >> +
> > >> inv_info->addr_info.addr, size,
> > >> +						granu);  
>  [...]  
>  [...]  
> > >>> pasid_info.pasid);  
> > >> +  
> > >
> > > as earlier comment, we shouldn't allow userspace or guest to
> > > invalidate PASID cache
> > >  
>  [...]  
> > >  
> 

[Jacob Pan]
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