linux-kernel - Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 21 Feb 2020 17:36:45 +0100
From:   Christoph Hellwig <hch@....de>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     Christoph Hellwig <hch@....de>, Halil Pasic <pasic@...ux.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Viktor Mihajlovski <mihajlov@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Ram Pai <linuxram@...ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Michael Mueller <mimu@...ux.ibm.com>
Subject: Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is
 protected

On Fri, Feb 21, 2020 at 01:59:15PM +1100, David Gibson wrote:
> > Hell no.  This is a detail of the platform DMA direct implementation.
> > Drivers have no business looking at this flag, and virtio finally needs
> > to be fixed to use the DMA API properly for everything but legacy devices.
> 
> So, this patch definitely isn't right as it stands, but I'm struggling
> to understand what it is you're saying is the right way.
> 
> By "legacy devices" I assume you mean pre-virtio-1.0 devices, that
> lack the F_VERSION_1 feature flag.  Is that right?  Because I don't
> see how being a legacy device or not relates to use of the DMA API.

No.   "legacy" is anything that does not set F_ACCESS_PLATFORM.

> I *think* what you are suggesting here is that virtio devices that
> have !F_IOMMU_PLATFORM should have their dma_ops set up so that the
> DMA API treats IOVA==PA, which will satisfy what the device expects.
> Then the virtio driver can use the DMA API the same way for both
> F_IOMMU_PLATFORM and !F_IOMMU_PLATFORM devices.

No.  Those should just keep using the existing legacy non-dma ops
case and be done with it.  No changes to that and most certainly
no new features.