Re: [PATCH v5 06/27] iommu/arm-smmu-v3: Consolidate clearing a CD table entry

From: Mostafa Saleh <smostafa@google.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: iommu@lists.linux.dev, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel@lists.infradead.org,
	Robin Murphy <robin.murphy@arm.com>,
	Will Deacon <will@kernel.org>, Eric Auger <eric.auger@redhat.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Moritz Fischer <mdf@kernel.org>,
	Michael Shavit <mshavit@google.com>,
	Nicolin Chen <nicolinc@nvidia.com>,
	patches@lists.linux.dev,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Subject: Re: [PATCH v5 06/27] iommu/arm-smmu-v3: Consolidate clearing a CD table entry
Date: Mon, 25 Mar 2024 21:02:45 +0000	[thread overview]
Message-ID: <ZgHmdXZ3ntMMSDtQ@google.com> (raw)
In-Reply-To: <20240325141433.GB110546@nvidia.com>

On Mon, Mar 25, 2024 at 11:14:33AM -0300, Jason Gunthorpe wrote:
> On Fri, Mar 22, 2024 at 06:36:17PM +0000, Mostafa Saleh wrote:
> > > +void arm_smmu_clear_cd(struct arm_smmu_master *master, ioasid_t ssid)
> > > +{
> > > +	struct arm_smmu_cd target = {};
> > > +	struct arm_smmu_cd *cdptr;
> > > +
> > > +	if (!master->cd_table.cdtab)
> > > +		return;
> > > +	cdptr = arm_smmu_get_cd_ptr(master, ssid);
> > > +	if (WARN_ON(!cdptr))
> > > +		return;
> > 
> > I don’t understand the SVA code enough, but AFAICT, arm_smmu_sva_set_dev_pasid
> > can allocate the L2 CD table through arm_smmu_write_ctx_desc. 
> 
> Yes
> 
> > And if it failed
> > before allocating the CD table, then remove_dev_pasid would be
> > called, 
> 
> If it fails the core code should not call remove_dev_pasid() on a
> domain that was never attached. There is an obscure error unwinding
> issue in the core code Yi is looking to fix regarding multi-device
> PASID groups, but it is not a driver issue..
> 

I see, thanks for clarifying.

> > which warns here, the previous code would tolerate that, but that
> > might regress on systems with panic_on_warn, so I am not sure if
> > that is necessary.
> 
> Right, if it does hit it signals there is some error unwinding bug in
> the core code that should be resolved.
> 
> > Otherwise, Reviewed-by: Mostafa Saleh <smostafa@google.com>
> 
> Thanks,
> Jason

Thanks,
Mostafa

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel