linux-kernel - Re: [RFC PATCH 01/12] dma-buf: Introduce dma_buf_get_pfn

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: <Z4Fz5oiia1JGWIgG@phenom.ffwll.local>
Date: Fri, 10 Jan 2025 20:24:22 +0100
From: Simona Vetter <simona.vetter@...ll.ch>
To: Xu Yilun <yilun.xu@...ux.intel.com>
Cc: Jason Gunthorpe <jgg@...dia.com>,
	Christian König <christian.koenig@....com>,
	Christoph Hellwig <hch@....de>, Leon Romanovsky <leonro@...dia.com>,
	kvm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
	sumit.semwal@...aro.org, pbonzini@...hat.com, seanjc@...gle.com,
	alex.williamson@...hat.com, vivek.kasireddy@...el.com,
	dan.j.williams@...el.com, aik@....com, yilun.xu@...el.com,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
	lukas@...ner.de, yan.y.zhao@...el.com, daniel.vetter@...ll.ch,
	leon@...nel.org, baolu.lu@...ux.intel.com, zhenzhong.duan@...el.com,
	tao1.su@...el.com
Subject: Re: [RFC PATCH 01/12] dma-buf: Introduce dma_buf_get_pfn_unlocked()
 kAPI

On Thu, Jan 09, 2025 at 01:56:02AM +0800, Xu Yilun wrote:
> > > > 5) iommufd and kvm are both using CPU addresses without DMA. No
> > > > exporter mapping is possible
> > > 
> > > We have customers using both KVM and XEN with DMA-buf, so I can clearly
> > > confirm that this isn't true.
> > 
> > Today they are mmaping the dma-buf into a VMA and then using KVM's
> > follow_pfn() flow to extract the CPU pfn from the PTE. Any mmapable
> > dma-buf must have a CPU PFN.
> 
> Yes, the final target for KVM is still the CPU PFN, just with the help
> of CPU mapping table.
> 
> I also found the xen gntdev-dmabuf is calculating pfn from mapped
> sgt.

See the comment, it's ok because it's a fake device with fake iommu and
the xen code has special knowledge to peek behind the curtain.
-Sima
 
> From Christion's point, I assume only sgl->dma_address should be
> used by importers but in fact not. More importers are 'abusing' sg dma
> helpers.
> 
> That said there are existing needs for importers to know more about the
> real buffer resource, for mapping, or even more than mapping,
> e.g. dmabuf_imp_grant_foreign_access()
-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch