linux-kernel - RE: [RFC PATCH 06/12] iommu: Add mmu

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Date:   Wed, 1 Nov 2023 11:58:46 +0000
From:   "Zhang, Tina" <tina.zhang@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: RE: [RFC PATCH 06/12] iommu: Add mmu_notifier to sva domain

Hi Jason,

> -----Original Message-----
> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Tuesday, October 24, 2023 2:35 AM
> To: Zhang, Tina <tina.zhang@...el.com>
> Cc: iommu@...ts.linux.dev; linux-kernel@...r.kernel.org; kvm@...r.kernel.org;
> David Woodhouse <dwmw2@...radead.org>; Lu Baolu
> <baolu.lu@...ux.intel.com>; Joerg Roedel <joro@...tes.org>; Tian, Kevin
> <kevin.tian@...el.com>
> Subject: Re: [RFC PATCH 06/12] iommu: Add mmu_notifier to sva domain
> 
> 
> On Tue, Oct 17, 2023 at 11:20:39AM +0800, Tina Zhang wrote:
> > Devices attached to shared virtual addressing (SVA) domain are allowed
> > to use the same virtual addresses with processor, and this
> > functionality is called shared virtual memory. When shared virtual
> > memory is being used, it's the sva domain's responsibility to keep
> > device TLB cache and the CPU cache in sync. Hence add mmu_notifier to sva
> domain.
> >
> > Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> > ---
> >  include/linux/iommu.h | 2 ++
> >  1 file changed, 2 insertions(+)
> 
> You should look at how arm smmuv3 ended up after I went over it to make
> similar changes, I think you should take this patch
> 
> https://lore.kernel.org/linux-iommu/20-v1-afbb86647bbd+5-
> smmuv3_newapi_p2_jgg@...dia.com/
> 
> into this series (maybe drop the arm part)
Good suggestion. The new domain_alloc_sva() callback allows drivers to fully initialize sva domain that is what we need. I'll take the domain_alloc_sva() part as a patch and include it in this patch-set. Thanks.

> 
> And copy the same basic structure for how the mmu notifier works.
> 
> It would also be nice if alot of the 'if_sva' tests could be avoided, smmu didn't
> end up with those..
Agree. With the help of domain_alloc_sva() callback, I think most of the if_sva brought by this RFC version can be reduced, as we can reuse fields from dmar_domain (or add new ones if necessary) and initialize them in domain_alloc_sva().

Regards,
-Tina
> 
> In the guts of the pasid handling sva shouldn't be special beyond a different
> source for the pgd.
> 
> Jason