linux-kernel - Re: [PATCH 07/12] iommu/vt-d: Cleanup use of iommu_flush_iotlb

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Message-ID: <a0e2bde5-1ec0-4b42-aa52-5f86e9e0822e@linux.intel.com>
Date: Sun, 7 Apr 2024 15:06:07 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, "Zhang, Tina" <tina.zhang@...el.com>,
 "Liu, Yi L" <yi.l.liu@...el.com>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/12] iommu/vt-d: Cleanup use of iommu_flush_iotlb_psi()

On 3/28/24 3:50 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Monday, March 25, 2024 10:17 AM
>>
>> Use cache_tag_flush_range() in switch_to_super_page() to invalidate the
>> necessary caches when switching mappings from normal to super pages. The
>> iommu_flush_iotlb_psi() call in intel_iommu_memory_notifier() is
>> unnecessary since there should be no cache invalidation for the identity
>> domain.
>>
> 
> what about a software identity domain?

Software identity domain is used to fake the hardware passthrough
capability, on early VT-d hardware which doesn't implement the
passthrough mode. It's not any kind of protection domain, hence the OS
is not required to manage the cache synchronization.

Although I hope we can remove it someday and force the DMA domain
instead, we still need to carry it nowadays. However, we need to make it
consistent with the hardware passthrough. That is, hardware passthrough
doesn't require any cache invalidation in memory hot-plug paths, the
software passthrough should not either.

Best regards,
baolu