linux-kernel - Re: [PATCH v6 6/6] iommu/tegra241-cmdqv: Limit CMDs for guest owned VINTF

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Date: Mon, 6 May 2024 10:00:05 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v6 6/6] iommu/tegra241-cmdqv: Limit CMDs for guest owned
 VINTF

On Sun, May 05, 2024 at 08:52:32PM -0700, Nicolin Chen wrote:
> On Tue, Apr 30, 2024 at 09:17:58PM -0300, Jason Gunthorpe wrote:
> > On Tue, Apr 30, 2024 at 11:58:44AM -0700, Nicolin Chen wrote:
> > > Otherwise, there has to be a get_suported_cmdq callback so batch
> > > or its callers can avoid adding unsupported commands at the first
> > > place.
> > 
> > If you really feel strongly the invalidation could be split into
> > S1/S2/S1_VM groupings that align with the feature bits and that could
> > be passed down from one step above. But I don't think the complexity
> > is really needed. It is better to deal with it through the feature
> > mechanism.
> 
> Hmm, I tried following your design by passing in a CMD_TYPE_xxx
> to the tegra241_cmdqv_get_cmdq(), but I found a little painful
> to accommodate these two cases:
> 1. TLBI_NH_ASID is issued via arm_smmu_cmdq_issue_cmdlist(), so
>    we should not mark it as CMD_TYPE_ALL. Yet, this function is
>    used by other commands too. So, either we pass in a type from
>    higher callers, or simply check the opcode in that function.

Yes, you'd have to pass in the type there too, which makes it more
ugly.

> So, it feels to me that checking against the opcode is still a
> straightforward solution. And what I ended up with is somewhat
> similar to this v6, yet this time it only checks at batch init
> call as your design does.

Well, the only downside is that the commands have to be same in a
batch, but maybe that is OK anyhow.

Don't forget to take the hunks that fix the queue as well.

Jason