From: Jason Gunthorpe <jgg@ziepe.ca>
To: Dan Williams <dan.j.williams@intel.com>
Cc: mhonap@nvidia.com, alwilliamson@nvidia.com,
jonathan.cameron@huawei.com, dave.jiang@intel.com,
alejandro.lucero-palau@amd.com, dave@stgolabs.net,
alison.schofield@intel.com, vishal.l.verma@intel.com,
ira.weiny@intel.com, dmatlack@google.com, shuah@kernel.org,
yishaih@nvidia.com, skolothumtho@nvidia.com,
kevin.tian@intel.com, ankita@nvidia.com, vsethi@nvidia.com,
cjia@nvidia.com, targupta@nvidia.com, zhiw@nvidia.com,
kjaju@nvidia.com, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org,
kvm@vger.kernel.org
Subject: Re: [PATCH v2 16/20] vfio/cxl: Register regions with VFIO layer
Date: Sat, 4 Apr 2026 15:53:30 -0300 [thread overview]
Message-ID: <20260404185330.GD2551565@ziepe.ca> (raw)
In-Reply-To: <69d0169115c06_1b0cc6100a5@dwillia2-mobl4.notmuch>
On Fri, Apr 03, 2026 at 12:35:45PM -0700, Dan Williams wrote:
> > + /*
> > + * CXL device memory is RAM, not MMIO. Use memremap() rather than
>
> Right, CXL.mem is RAM, not MMIO, so I question why is this not being
> mapped via a RAM mechanism? Can you explain a bit more about why reusing
> vfio MMIO mapping mechanisms is suitable here and what happens when we
> get to questions like guest_memfd integration, page conversions, and
> large page mapping support?
None of that is applicable to VFIO. VFIO owns the entire address space
and does not share it with the mm or anything else.
> Maybe this is the start of the conversation for something simple, but I
> would actually prefer uncached ioremap() if only to avoid all the
> coherence management and suitability of MMIO mechanisms questions.
The entire thing needs to be mmapable in a cache coherent way since
that is what the HW semantic is. If you try to do something else you
will break KVM support since it follows the VMA.
Jason
next prev parent reply other threads:[~2026-04-04 18:53 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-01 14:38 [PATCH v2 00/20] vfio/pci: Add CXL Type-2 device passthrough support mhonap
2026-04-01 14:38 ` [PATCH v2 01/20] cxl: Add cxl_get_hdm_info() for HDM decoder metadata mhonap
2026-04-01 14:38 ` [PATCH v2 02/20] cxl: Declare cxl_find_regblock and cxl_probe_component_regs in public header mhonap
2026-04-01 14:39 ` [PATCH v2 03/20] cxl: Move component/HDM register defines to uapi/cxl/cxl_regs.h mhonap
2026-04-01 14:39 ` [PATCH v2 04/20] cxl: Split cxl_await_range_active() from media-ready wait mhonap
2026-04-01 14:39 ` [PATCH v2 05/20] cxl: Record BIR and BAR offset in cxl_register_map mhonap
2026-04-01 14:39 ` [PATCH v2 06/20] vfio: UAPI for CXL-capable PCI device assignment mhonap
2026-04-01 14:39 ` [PATCH v2 07/20] vfio/pci: Add CXL state to vfio_pci_core_device mhonap
2026-04-01 14:39 ` [PATCH v2 08/20] vfio/pci: Add CONFIG_VFIO_CXL_CORE and stub CXL hooks mhonap
2026-04-01 14:39 ` [PATCH v2 09/20] vfio/cxl: Detect CXL DVSEC and probe HDM block mhonap
2026-04-01 14:39 ` [PATCH v2 10/20] vfio/pci: Export config access helpers mhonap
2026-04-01 14:39 ` [PATCH v2 11/20] vfio/cxl: Introduce HDM decoder register emulation framework mhonap
2026-04-01 14:39 ` [PATCH v2 12/20] vfio/cxl: Wait for HDM ranges and create memdev mhonap
2026-04-01 14:39 ` [PATCH v2 13/20] vfio/cxl: CXL region management support mhonap
2026-04-01 14:39 ` [PATCH v2 14/20] vfio/cxl: DPA VFIO region with demand fault mmap and reset zap mhonap
2026-04-01 14:39 ` [PATCH v2 15/20] vfio/cxl: Virtualize CXL DVSEC config writes mhonap
2026-04-01 14:39 ` [PATCH v2 16/20] vfio/cxl: Register regions with VFIO layer mhonap
2026-04-03 19:35 ` Dan Williams
2026-04-04 18:53 ` Jason Gunthorpe [this message]
2026-04-04 19:36 ` Dan Williams
2026-04-06 21:22 ` Gregory Price
2026-04-06 22:05 ` Jason Gunthorpe
2026-04-06 22:10 ` Jason Gunthorpe
2026-04-01 14:39 ` [PATCH v2 17/20] vfio/pci: Advertise CXL cap and sparse component BAR to userspace mhonap
2026-04-01 14:39 ` [PATCH v2 18/20] vfio/cxl: Provide opt-out for CXL feature mhonap
2026-04-01 14:39 ` [PATCH v2 19/20] docs: vfio-pci: Document CXL Type-2 device passthrough mhonap
2026-04-01 14:39 ` [PATCH v2 20/20] selftests/vfio: Add CXL Type-2 VFIO assignment test mhonap
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