linux-kernel - Re: [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace

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Message-ID: <Y+pNEtgyAJwLjERa@nvidia.com>
Date:   Mon, 13 Feb 2023 10:45:38 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>
Subject: Re: [PATCH v2 02/10] iommu: Introduce a new
 iommu_group_replace_domain() API

On Mon, Feb 13, 2023 at 02:24:40AM +0000, Tian, Kevin wrote:

> > This is because the cache tag and the io page table top are in
> > different 64 bit words so atomic writes don't cover both, and thus the
> > IOMMU HW could tear the two stores and mismatch the cache tag to the
> > table top. This would corrupt the cache.
> 
> VT-d spec recommends using 128bit cmpxchg instruction to update
> page table pointer and DID together.

Oh really? Such a thing exists? That neat!

Jason