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Thu, 7 May 2026 07:17:27 +0000 Message-ID: <3128deea-95a3-4c36-902b-37f280913f2b@amd.com> Date: Thu, 7 May 2026 17:16:56 +1000 User-Agent: Mozilla Thunderbird Beta Subject: Re: [RFC PATCH 04/12] vfio/pci: Allow MMIO regions to be exported through dma-buf To: Jason Gunthorpe Cc: Xu Yilun , kvm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, sumit.semwal@linaro.org, christian.koenig@amd.com, pbonzini@redhat.com, seanjc@google.com, alex.williamson@redhat.com, vivek.kasireddy@intel.com, dan.j.williams@intel.com, yilun.xu@intel.com, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, lukas@wunner.de, yan.y.zhao@intel.com, daniel.vetter@ffwll.ch, leon@kernel.org, baolu.lu@linux.intel.com, zhenzhong.duan@intel.com, tao1.su@intel.com References: <20250107142719.179636-1-yilun.xu@linux.intel.com> <20250107142719.179636-5-yilun.xu@linux.intel.com> From: Alexey Kardashevskiy Content-Language: en-US In-Reply-To: Content-Type: text/plain; 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And it's been fine until I got a device where MSIX BAR is in a middle of another BAR marked as TEE in the TDISP interface report. And no trusted MSIX yet. >> >> Every time QEMU mmaps a BAR - I request a dmabuf fd from VFIO in QEMU. Since mapping of an entire MSIX BAR is allowed by default, VFIORegion::nr_mmaps==1 and it is an entire BAR. >> >> Problem: KVM memslot mismatches the dmabuf fd size > > Huh? kvm does not care about dmabuf at all? Are you running other > patches to hook kvm and dmabuf? yup, 06/12 of this patchset. > Putting a slice in a dmabuf is a well understood need for MSI, so I > expect whatever kvm dmabuf interface that gets merged to accomodate > this? good to know. >> Solution2: modify logic in VFIO dmabuf to allow multiple KVM memory >> slots per dmabuf. Now it is kvm_memory_slot::dmabuf_attach with no >> offset into the dmabuf and one kvm_vfio_dmabuf per dma_buf. > > Yes, when kvm learns to take in a dmabuf it needs to take in a slice, > not the whole buf. Or you need to create multiple dmabufs with the > necessary slices from the VFIO. The upstream vfio dmabuf creation > allows creating it with a slice. true but either way dmabuf slicing will be directed by QEMU's msix-table emulation MR and this slicing needs to match the TDISP report so I'll have to teach QEMU these reports, right? I am worried if I miss something obvious, again. Thanks, ps. I like nntp.lore.kernel.org very much for ability to dig out old stuff and then just reply to it :) > > Jason -- Alexey