linux-kernel - Re: [PATCH v8 09/11] vfio/pci: Enable peer-to-peer DMA transactions by default

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]

Message-ID: <20251118131038.32b7804d.alex@shazbot.org>
Date: Tue, 18 Nov 2025 13:10:38 -0700
From: Alex Williamson <alex@...zbot.org>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Leon Romanovsky <leon@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Logan Gunthorpe <logang@...tatee.com>, Jens Axboe <axboe@...nel.dk>,
 "Robin Murphy" <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 "Jason Gunthorpe" <jgg@...pe.ca>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 "Ankit Agrawal" <ankita@...dia.com>, Yishai Hadas <yishaih@...dia.com>,
 "Shameer Kolothum" <skolothumtho@...dia.com>,
 Krishnakant Jaju <kjaju@...dia.com>, Matt Ochs <mochs@...dia.com>,
 "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
 "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
 Alex Mastro <amastro@...com>, Nicolin Chen <nicolinc@...dia.com>
Subject: Re: [PATCH v8 09/11] vfio/pci: Enable peer-to-peer DMA transactions
 by default

On Tue, 18 Nov 2025 07:18:36 +0000
"Tian, Kevin" <kevin.tian@...el.com> wrote:

> > From: Leon Romanovsky <leon@...nel.org>
> > Sent: Tuesday, November 11, 2025 5:58 PM
> > 
> > From: Leon Romanovsky <leonro@...dia.com>  
> 
> not required with only your own s-o-b
> 
> > @@ -2090,6 +2092,9 @@ int vfio_pci_core_init_dev(struct vfio_device
> > *core_vdev)
> >  	INIT_LIST_HEAD(&vdev->dummy_resources_list);
> >  	INIT_LIST_HEAD(&vdev->ioeventfds_list);
> >  	INIT_LIST_HEAD(&vdev->sriov_pfs_item);
> > +	ret = pcim_p2pdma_init(vdev->pdev);
> > +	if (ret && ret != -EOPNOTSUPP)
> > +		return ret;  
> 
> Reading the commit msg seems -EOPNOTSUPP is only returned for fake
> PCI devices, otherwise it implies regression. better add a comment for it?

I think the commit log is saying that if a device comes along that
can't support this, we'd quirk the init path to return -EOPNOTSUPP for
that particular device here.  This path is currently used when
!CONFIG_PCI_P2PDMA to make this error non-fatal to the device init.

I don't see a regression if such a device comes along and while we
could survive other types of failures by disabling p2pdma here, I think
all such cases are sufficient rare out of memory cases to consider them
catastrophic.  Thanks,

Alex