From: Jason Gunthorpe <jgg@nvidia.com>
To: "Christian König" <christian.koenig@amd.com>
Cc: "Alex Mastro" <amastro@fb.com>, "Matt Evans" <mattev@meta.com>,
"Alex Williamson" <alex@shazbot.org>,
"Leon Romanovsky" <leon@kernel.org>,
"Mahmoud Adam" <mngyadam@amazon.de>,
"David Matlack" <dmatlack@google.com>,
"Björn Töpel" <bjorn@kernel.org>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Kevin Tian" <kevin.tian@intel.com>,
"Ankit Agrawal" <ankita@nvidia.com>,
"Pranjal Shrivastava" <praan@google.com>,
"Alistair Popple" <apopple@nvidia.com>,
"Vivek Kasireddy" <vivek.kasireddy@intel.com>,
linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
kvm@vger.kernel.org
Subject: Re: [RFC PATCH 3/7] vfio/pci: Support mmap() of a DMABUF
Date: Mon, 2 Mar 2026 08:54:55 -0400 [thread overview]
Message-ID: <20260302125455.GU5933@nvidia.com> (raw)
In-Reply-To: <b729ebe1-aea2-4f45-bb3f-3b4b59078c8d@amd.com>
On Mon, Mar 02, 2026 at 11:07:41AM +0100, Christian König wrote:
> As far as I know background is that on x86 pte_special() only works
> on true leave pte but not pmd/pud.
This is not the case, there are pmd and pud_special as well, protected
by CONFIG_xx
The arch should not define CONFIG_ARCH_SUPPORTS_PMD_PFNMAP if
vmf_insert_pfn_pmd() doesn't result in pmd_special() working, for
example.
eg:
vmf_insert_pfn_pmd()
insert_pmd()
if (fop.is_folio) {
// Not Taken
} else {
entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot));
entry = pmd_mkspecial(entry);
This stuff was all put together by Peter specifically for VFIO to use,
AFAIK it is correct.
IDK what Thomas was using, but if you tried to do huge faults before
all of this was built it definitely would not work right as it only
supported a folio backed path.
Jason
next prev parent reply other threads:[~2026-03-02 12:55 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-26 20:21 [RFC PATCH 0/7] vfio/pci: Add mmap() for DMABUFs Matt Evans
2026-02-26 20:21 ` [RFC PATCH 1/7] vfio/pci: Ensure VFIO barmap is set up before creating a DMABUF Matt Evans
2026-02-26 20:21 ` [RFC PATCH 2/7] vfio/pci: Clean up DMABUFs before disabling function Matt Evans
2026-02-26 20:21 ` [RFC PATCH 3/7] vfio/pci: Support mmap() of a DMABUF Matt Evans
2026-02-27 10:09 ` Christian König
2026-02-27 12:51 ` Jason Gunthorpe
2026-02-27 19:42 ` Matt Evans
2026-02-27 19:48 ` Jason Gunthorpe
2026-02-27 21:52 ` Alex Mastro
2026-02-27 22:00 ` Alex Mastro
2026-02-27 22:04 ` Jason Gunthorpe
2026-03-02 10:07 ` Christian König
2026-03-02 12:54 ` Jason Gunthorpe [this message]
2026-03-02 13:20 ` Christian König
2026-02-26 20:22 ` [RFC PATCH 4/7] dma-buf: uapi: Mechanism to revoke DMABUFs via ioctl() Matt Evans
2026-02-27 10:05 ` Christian König
2026-02-27 12:56 ` Jason Gunthorpe
2026-02-27 13:02 ` Matt Evans
2026-02-27 15:20 ` Christian König
2026-02-27 16:19 ` Matt Evans
2026-02-26 20:22 ` [RFC PATCH 5/7] vfio/pci: Permanently revoke a DMABUF on request Matt Evans
2026-02-26 20:22 ` [RFC PATCH 6/7] vfio/pci: Add mmap() attributes to DMABUF feature Matt Evans
2026-02-26 20:22 ` [RFC PATCH 7/7] [RFC ONLY] selftests: vfio: Add standalone vfio_dmabuf_mmap_test Matt Evans
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