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

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Message-ID: <BN9PR11MB52761B8A7D11C39DDE0FFA5E8C002@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Mon, 8 Apr 2024 02:57:26 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <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>
CC: "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()

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Sunday, April 7, 2024 3:06 PM
> 
> 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.
> 

yes, that makes sense.