linux-kernel - Re: [RFC PATCH v1 3/8] iommu/arm-smmu-v3-sva: Allocate new ASID from installed

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Message-ID: <ZONQgNh6qarqgA+f@nvidia.com>
Date:   Mon, 21 Aug 2023 08:54:40 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, will@...nel.org, nicolinc@...dia.com,
        tina.zhang@...el.com, jean-philippe@...aro.org,
        robin.murphy@....com
Subject: Re: [RFC PATCH v1 3/8] iommu/arm-smmu-v3-sva: Allocate new ASID from
 installed_smmus

On Mon, Aug 21, 2023 at 05:31:23PM +0800, Michael Shavit wrote:
> On Fri, Aug 18, 2023 at 2:38 AM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > On Fri, Aug 18, 2023 at 02:16:25AM +0800, Michael Shavit wrote:
> > > Pick an ASID that is within the supported range of all SMMUs that the
> > > domain is installed to.
> > >
> > > Signed-off-by: Michael Shavit <mshavit@...gle.com>
> > > ---
> >
> > This seems like a pretty niche scenario, maybe we should just keep a
> > global for the max ASID?
> >
> > Otherwise we need a code to change the ASID, even for non-SVA domains,
> > when the domain is installed in different devices if the current ASID
> > is over the instance max..
> 
> This RFC took the other easy way out for this problem by rejecting
> attaching a domain if its currently assigned ASID/VMID
> is out of range when attaching to a new SMMU. But I'm not sure
> which of the two options is the right trade-off.
> Especially if we move VMID to a global allocator (which I plan to add
> for v2), setting a global maximum for VMID of 256 sounds small.

IMHO the simplest and best thing is to make both vmid and asid as
local allocators. Then alot of these problems disappear

Jason