From: Jason Gunthorpe <jgg@nvidia.com>
To: Christoph Hellwig <hch@lst.de>
Cc: "Leon Romanovsky" <leon@kernel.org>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Christian König" <christian.koenig@amd.com>,
dri-devel@lists.freedesktop.org, iommu@lists.linux.dev,
"Jens Axboe" <axboe@kernel.dk>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Joerg Roedel" <joro@8bytes.org>,
kvm@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-media@vger.kernel.org, linux-mm@kvack.org,
linux-pci@vger.kernel.org,
"Logan Gunthorpe" <logang@deltatee.com>,
"Marek Szyprowski" <m.szyprowski@samsung.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Vivek Kasireddy" <vivek.kasireddy@intel.com>,
"Will Deacon" <will@kernel.org>
Subject: Re: [PATCH 02/10] PCI/P2PDMA: Introduce p2pdma_provider structure for cleaner abstraction
Date: Sun, 27 Jul 2025 15:51:58 -0300 [thread overview]
Message-ID: <20250727185158.GE7551@nvidia.com> (raw)
In-Reply-To: <20250724075922.GD30590@lst.de>
On Thu, Jul 24, 2025 at 09:59:22AM +0200, Christoph Hellwig wrote:
> On Thu, Jul 24, 2025 at 10:55:33AM +0300, Leon Romanovsky wrote:
> > Please, see last patch in the series https://lore.kernel.org/all/aea452cc27ca9e5169f7279d7b524190c39e7260.1753274085.git.leonro@nvidia.com
> > It gives me a way to call p2p code with stable pointer for whole BAR.
> >
>
> That simply can't work.
Why not?
That's the whole point of this, to remove struct page and use
something else as a handle for the p2p when doing the DMA API stuff.
The caller must make sure the lifetimes all work out. The handle must
live longer than any active DMAs, etc, etc. DMABUF with invalidation
lets vfio do that.
This is why the DMA api code was taught to use phys_addr_t and not
touch the struct page so it could work with struct-pageless memory.
The idea was to end up with two layers in the P2P code where the lower
layer only works on the handle, and then there is an optional struct
page/genalloc/etc layer for places that want struct page and mmap.
Jason
next prev parent reply other threads:[~2025-07-27 18:52 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-23 13:00 [PATCH 00/10] vfio/pci: Allow MMIO regions to be exported through dma-buf Leon Romanovsky
2025-07-23 13:00 ` [PATCH 01/10] PCI/P2PDMA: Remove redundant bus_offset from map state Leon Romanovsky
2025-07-24 7:50 ` Christoph Hellwig
2025-07-23 13:00 ` [PATCH 02/10] PCI/P2PDMA: Introduce p2pdma_provider structure for cleaner abstraction Leon Romanovsky
2025-07-24 7:51 ` Christoph Hellwig
2025-07-24 7:55 ` Leon Romanovsky
2025-07-24 7:59 ` Christoph Hellwig
2025-07-24 8:07 ` Leon Romanovsky
2025-07-27 18:51 ` Jason Gunthorpe [this message]
2025-07-29 7:52 ` Christoph Hellwig
2025-07-29 8:53 ` Leon Romanovsky
2025-07-29 10:41 ` Christoph Hellwig
2025-07-29 11:39 ` Leon Romanovsky
2025-07-29 13:15 ` Jason Gunthorpe
2025-07-29 16:12 ` Jason Gunthorpe
2025-07-23 13:00 ` [PATCH 03/10] PCI/P2PDMA: Simplify bus address mapping API Leon Romanovsky
2025-07-24 7:52 ` Christoph Hellwig
2025-07-23 13:00 ` [PATCH 04/10] PCI/P2PDMA: Refactor to separate core P2P functionality from memory allocation Leon Romanovsky
2025-07-23 13:00 ` [PATCH 05/10] PCI/P2PDMA: Export pci_p2pdma_map_type() function Leon Romanovsky
2025-07-24 8:03 ` Christoph Hellwig
2025-07-24 8:13 ` Leon Romanovsky
2025-07-25 16:30 ` Logan Gunthorpe
2025-07-25 18:54 ` Leon Romanovsky
2025-07-25 19:12 ` Logan Gunthorpe
2025-07-27 6:01 ` Leon Romanovsky
2025-07-27 19:05 ` Jason Gunthorpe
2025-07-28 16:12 ` Logan Gunthorpe
2025-07-28 16:41 ` Leon Romanovsky
2025-07-28 17:07 ` Logan Gunthorpe
2025-07-28 23:11 ` Jason Gunthorpe
2025-07-29 20:54 ` Logan Gunthorpe
2025-07-29 22:14 ` Jason Gunthorpe
2025-07-30 8:03 ` Leon Romanovsky
2025-07-29 7:52 ` Christoph Hellwig
2025-07-29 8:45 ` Leon Romanovsky
2025-07-27 19:02 ` Jason Gunthorpe
2025-07-23 13:00 ` [PATCH 06/10] types: move phys_vec definition to common header Leon Romanovsky
2025-07-23 13:00 ` [PATCH 07/10] vfio: Export vfio device get and put registration helpers Leon Romanovsky
2025-07-23 13:00 ` [PATCH 08/10] vfio/pci: Enable peer-to-peer DMA transactions by default Leon Romanovsky
2025-07-23 13:00 ` [PATCH 09/10] vfio/pci: Share the core device pointer while invoking feature functions Leon Romanovsky
2025-07-28 20:55 ` Alex Williamson
2025-07-29 8:39 ` Leon Romanovsky
2025-07-23 13:00 ` [PATCH 10/10] vfio/pci: Add dma-buf export support for MMIO regions Leon Romanovsky
2025-07-24 5:13 ` Kasireddy, Vivek
2025-07-24 5:44 ` Leon Romanovsky
2025-07-25 5:34 ` Kasireddy, Vivek
2025-07-27 6:16 ` Leon Romanovsky
2025-07-29 19:44 ` Robin Murphy
2025-07-29 20:13 ` Jason Gunthorpe
2025-07-30 9:32 ` Leon Romanovsky
2025-07-30 14:49 ` Robin Murphy
2025-07-30 16:01 ` Jason Gunthorpe
2025-07-30 19:58 ` [PATCH 00/10] vfio/pci: Allow MMIO regions to be exported through dma-buf Alex Williamson
2025-07-31 0:21 ` Jason Gunthorpe
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