linux-kernel - Re: [PATCH v1 15/16] iommu/arm-smmu-v3: Add viommu cache invalidation support

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Message-ID: <20240819173615.GN2032816@nvidia.com>
Date: Mon, 19 Aug 2024 14:36:15 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1 15/16] iommu/arm-smmu-v3: Add viommu cache
 invalidation support

On Thu, Aug 15, 2024 at 05:50:06PM -0700, Nicolin Chen wrote:

> Though only driver would know whether it would eventually access
> the vdev_id list, I'd like to keep things in the way of having a
> core-managed VIOMMU object (IOMMU_VIOMMU_TYPE_DEFAULT), so the
> viommu invalidation handler could have a lock at its top level to
> protect any potential access to the vdev_id list.

It is a bit tortured to keep the xarray hidden. It would be better to
find a way to expose the right struct to the driver.

> > > @@ -3249,6 +3266,19 @@ arm_smmu_convert_user_cmd(struct arm_smmu_domain *s2_parent,
> > >  		cmd->cmd[0] &= ~CMDQ_TLBI_0_VMID;
> > >  		cmd->cmd[0] |= FIELD_PREP(CMDQ_TLBI_0_VMID, vmid);
> > >  		break;
> > > +	case CMDQ_OP_ATC_INV:
> > > +	case CMDQ_OP_CFGI_CD:
> > > +	case CMDQ_OP_CFGI_CD_ALL:
> > 
> > Oh, I didn't catch on that CD was needing this too.. :\
> 
> Well, viommu cache has a very wide range :)
> 
> > That makes the other op much more useless than I expected. I really
> > wanted to break these two series apart.
> 
> HWPT invalidate and VIOMMU invalidate are somewhat duplicated in
> both concept and implementation for SMMUv3. It's not a problem to
> have both but practically I can't think of the reason why VMM not
> simply stick to the wider VIOMMU invalidate uAPI alone..
> 
> > Maybe we need to drop the hwpt invalidation from the other series and
> 
> Yea, the hwpt invalidate is just one patch in your series, it's
> easy to move if we want to.

> > aim to merge this all together through the iommufd tree.
> 
> I have been hoping for that, as you can see those driver patches
> are included here :)

Well, this series has to go through iommufd of course

I was hoping will could take the nesting enablement and we'd do the
viommu next window.

But nesting enablment with out viommu is alot less useful than I had
thought :(

So maybe Will acks the nesting patches and we take the bunch together.

Jason