Date: Tue, 28 Mar 2023 13:52:00 -0700
From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Baolu Lu <baolu.lu@linux.intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>, iommu@lists.linux.dev, Jason
 Gunthorpe <jgg@nvidia.com>, Joerg Roedel <joro@8bytes.org>,
 dmaengine@vger.kernel.org, vkoul@kernel.org, Robin Murphy
 <robin.murphy@arm.com>, Will Deacon <will@kernel.org>, David Woodhouse
 <dwmw2@infradead.org>, Raj Ashok <ashok.raj@intel.com>, "Tian, Kevin"
 <kevin.tian@intel.com>, Yi Liu <yi.l.liu@intel.com>, "Yu, Fenghua"
 <fenghua.yu@intel.com>, Dave Jiang <dave.jiang@intel.com>, Tony Luck
 <tony.luck@intel.com>, "Zanussi, Tom" <tom.zanussi@intel.com>,
 jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v2 4/8] iommu/vt-d: Reserve RID_PASID from global SVA
 PASID space
Message-ID: <20230328135200.139f280a@jacob-builder>
In-Reply-To: <20230328092919.372f0545@jacob-builder>
References: <20230327232138.1490712-1-jacob.jun.pan@linux.intel.com>
	<20230327232138.1490712-5-jacob.jun.pan@linux.intel.com>
	<41d31adf-577e-431c-c400-2708885400c1@linux.intel.com>
	<20230328092919.372f0545@jacob-builder>
Organization: OTC
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

Hi Baolu,

On Tue, 28 Mar 2023 09:29:19 -0700, Jacob Pan
<jacob.jun.pan@linux.intel.com> wrote:

> > > On VT-d platforms, RID_PASID is used for DMA request without PASID. We
> > > should not treat RID_PASID special instead let it be allocated from
> > > the global SVA PASID number space.    
> > 
> > It's same to AMD and ARM SMMUv3, right? They also need an explicit
> > reservation of PASID 0.
> >   
> yes, all IOMMU drivers need to do that. I will give it a try but might
> need help to place the call.
It might be simpler to just let SVA code allocate from 1 up instead of 0
(as is in the current code). Global PASID allocator would still allow the
full range from 0 to max. Then there is no change to architectures that
don't support non-zero RID_PASID. For VT-d, it would still work in the
future when we have nonzero RID_PASID. is that reasonable?

Thanks,

Jacob