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Message-ID: <c8373d68-9f15-e9a5-d19f-c050f23ac85d@linux.intel.com>
Date:   Mon, 10 Apr 2023 09:59:45 +0800
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Cc:     baolu.lu@linux.intel.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>
Subject: Re: [PATCH v4 4/7] iommu/vt-d: Reserve RID_PASID from global PASID
 space
Content-Language: en-US
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>, iommu@lists.linux.dev,
        Robin Murphy <robin.murphy@arm.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Joerg Roedel <joro@8bytes.org>, dmaengine@vger.kernel.org,
        vkoul@kernel.org
References: <20230407180554.2784285-1-jacob.jun.pan@linux.intel.com>
 <20230407180554.2784285-5-jacob.jun.pan@linux.intel.com>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <20230407180554.2784285-5-jacob.jun.pan@linux.intel.com>
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On 4/8/23 2:05 AM, Jacob Pan 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 PASID number space. Non-zero value can be used in RID_PASID on
> Intel VT-d.
> 
> For ARM, AMD and others that_always_  use 0 as RID_PASID, there is no
> impact in that SVA PASID allocation base is 1.
> 
> With this change, devices do both DMA with PASID and SVA will not worry
> about conflicts when it comes to allocating PASIDs for in-kernel DMA.
> 
> Signed-off-by: Jacob Pan<jacob.jun.pan@linux.intel.com>
> ---
>   drivers/iommu/intel/iommu.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 9f737ef55463..cbb2670f88ca 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -3956,6 +3956,10 @@ int __init intel_iommu_init(void)
>   
>   	intel_iommu_enabled = 1;
>   
> +	/* Reserved RID_PASID from the global namespace for legacy DMA */
> +	WARN_ON(iommu_alloc_global_pasid(PASID_RID2PASID, PASID_RID2PASID) !=
> +		PASID_RID2PASID);

How about moving above line up a bit? For example, at least before
iommu_device_register(). This is the starting point where device drivers
may want global PASIDs.

Best regards,
baolu