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Mon, 29 Sep 2025 14:17:44 -0700 (PDT) X-Google-Smtp-Source: AGHT+IG3VrvxaH7k00bkTZJWrxcv/Xeuv7Ik/zOnPnH3ASkfKmA5ptZ34qoyLfGaDXRfunQjFfs8kg== X-Received: by 2002:a05:6e02:1525:b0:408:1624:b2ee with SMTP id e9e14a558f8ab-425955e4f60mr87964675ab.1.1759180663680; Mon, 29 Sep 2025 14:17:43 -0700 (PDT) Received: from redhat.com ([38.15.36.11]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-57269f5d0c5sm1963571173.13.2025.09.29.14.17.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Sep 2025 14:17:42 -0700 (PDT) Date: Mon, 29 Sep 2025 15:17:40 -0600 From: Alex Williamson To: Leon Romanovsky Cc: Leon Romanovsky , Jason Gunthorpe , Andrew Morton , Bjorn Helgaas , Christian =?UTF-8?B?S8O2bmln?= , dri-devel@lists.freedesktop.org, iommu@lists.linux.dev, Jens Axboe , Joerg Roedel , 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 , Marek Szyprowski , Robin Murphy , Sumit Semwal , Vivek Kasireddy , Will Deacon Subject: Re: [PATCH v4 07/10] vfio/pci: Add dma-buf export config for MMIO regions Message-ID: <20250929151740.21f001e3.alex.williamson@redhat.com> In-Reply-To: References: X-Mailer: Claws Mail 4.3.1 (GTK 3.24.43; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 28 Sep 2025 17:50:17 +0300 Leon Romanovsky wrote: > From: Leon Romanovsky > > Add new kernel config which indicates support for dma-buf export > of MMIO regions, which implementation is provided in next patches. > > Signed-off-by: Leon Romanovsky > --- > drivers/vfio/pci/Kconfig | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig > index 2b0172f54665..55ae888bf26a 100644 > --- a/drivers/vfio/pci/Kconfig > +++ b/drivers/vfio/pci/Kconfig > @@ -55,6 +55,26 @@ config VFIO_PCI_ZDEV_KVM > > To enable s390x KVM vfio-pci extensions, say Y. > > +config VFIO_PCI_DMABUF > + bool "VFIO PCI extensions for DMA-BUF" > + depends on VFIO_PCI_CORE > + depends on PCI_P2PDMA && DMA_SHARED_BUFFER > + default y > + help > + Enable support for VFIO PCI extensions that allow exporting > + device MMIO regions as DMA-BUFs for peer devices to access via > + peer-to-peer (P2P) DMA. > + > + This feature enables a VFIO-managed PCI device to export a portion > + of its MMIO BAR as a DMA-BUF file descriptor, which can be passed > + to other userspace drivers or kernel subsystems capable of > + initiating DMA to that region. > + > + Say Y here if you want to enable VFIO DMABUF-based MMIO export > + support for peer-to-peer DMA use cases. > + > + If unsure, say N. > + > source "drivers/vfio/pci/mlx5/Kconfig" > > source "drivers/vfio/pci/hisilicon/Kconfig" This is only necessary if we think there's a need to build a kernel with P2PDMA and VFIO_PCI, but not VFIO_PCI_DMABUF. Does that need really exist? I also find it unusual to create the Kconfig before adding the supporting code. Maybe this could be popped to the end or rolled into the last patch if we decided to keep it. Thanks, Alex