linux-kernel - Re: [RFC PATCH v3 7/8] vfio/type1: Add selective DMA faulting support

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Date:   Fri, 21 May 2021 14:39:12 +0800
From:   Shenming Lu <lushenming@...wei.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>
CC:     Cornelia Huck <cohuck@...hat.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>,
        Eric Auger <eric.auger@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <linux-api@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>, <yi.l.liu@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        <wanghaibin.wang@...wei.com>, <yuzenghui@...wei.com>
Subject: Re: [RFC PATCH v3 7/8] vfio/type1: Add selective DMA faulting support

On 2021/5/19 2:58, Alex Williamson wrote:
> On Fri, 9 Apr 2021 11:44:19 +0800
> Shenming Lu <lushenming@...wei.com> wrote:
> 
>> Some devices only allow selective DMA faulting. Similar to the selective
>> dirty page tracking, the vendor driver can call vfio_pin_pages() to
>> indicate the non-faultable scope, we add a new struct vfio_range to
>> record it, then when the IOPF handler receives any page request out
>> of the scope, we can directly return with an invalid response.
> 
> Seems like this highlights a deficiency in the design, that the user
> can't specify mappings as iopf enabled or disabled.  Also, if the
> vendor driver has pinned pages within the range, shouldn't that prevent
> them from faulting in the first place?  Why do we need yet more
> tracking structures?  Pages pinned by the vendor driver need to count
> against the user's locked memory limits regardless of iopf.  Thanks,

Currently we only have a vfio_pfn struct to track the external pinned pages
(single page granularity), so I add a vfio_range struct for efficient lookup.

Yeah, by this patch, for the non-pinned scope, we can directly return INVALID,
but for the pinned(non-faultable) scope, tracking the pinned range doesn't seem
to help more...

Thanks,
Shenming

> 
> Alex
> 
> .
>