linux-kernel - Re: [PATCH v3 1/2] iommu/vt-d: Add helper to flush caches for context change

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Date: Tue, 2 Jul 2024 12:43:41 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>,
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] iommu/vt-d: Add helper to flush caches for context
 change

On 2024/7/2 12:41, Jacob Pan wrote:
> On Mon,  1 Jul 2024 19:23:16 +0800, Lu Baolu<baolu.lu@...ux.intel.com>
> wrote:
> 
>> +	if (flush_domains) {
>> +		/*
>> +		 * If the IOMMU is running in scalable mode and there
>> might
>> +		 * be potential PASID translations, the caller should
>> hold
>> +		 * the lock to ensure that context changes and cache
>> flushes
>> +		 * are atomic.
>> +		 */
>> +		assert_spin_locked(&iommu->lock);
>> +		for (i = 0; i < info->pasid_table->max_pasid; i++) {
>> +			pte = intel_pasid_get_entry(info->dev, i);
>> +			if (!pte || !pasid_pte_is_present(pte))
>> +				continue;
> Is it worth going through 1M PASIDs just to skip the PASID cache
> invalidation? Or just do the flush on all used DIDs unconditionally.

Currently we don't track all domains attached to a device. If such
optimization is necessary, perhaps we can add it later.

Best regards,
baolu