linux-kernel - RE: [RFC 10/20] iommu/iommufd: Add IOMMU_DEVICE_GET

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Date:   Thu, 14 Oct 2021 08:01:49 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
CC:     Jason Gunthorpe <jgg@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "hch@....de" <hch@....de>, "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "corbet@....net" <corbet@....net>,
        "parav@...lanox.com" <parav@...lanox.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>
Subject: RE: [RFC 10/20] iommu/iommufd: Add IOMMU_DEVICE_GET_INFO

> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Sent: Thursday, September 30, 2021 6:33 PM
> 
> The PTE flags define whether the memory access is cache-coherent or not.
> * WB is cacheable (short for write-back cacheable. Doesn't matter here
>   what OI or RWA mean.)
> * NC is non-cacheable.
> 
>          | Normal PCI access | No_snoop PCI access
>   -------+-------------------+-------------------
>   PTE WB | Cacheable         | Non-cacheable
>   PTE NC | Non-cacheable     | Non-cacheable

This implies that PCI no-snoop supersedes PTE flags when it's supported
by the system?