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Message-ID: <1bd43ef7-0403-bd25-087c-d54d5af677e4@deltatee.com>
Date: Tue, 5 Jul 2022 11:32:23 -0600
From: Logan Gunthorpe <logang@...tatee.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Christoph Hellwig <hch@....de>
Cc: Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org,
linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
linux-pci@...r.kernel.org, linux-mm@...ck.org,
iommu@...ts.linux-foundation.org,
Stephen Bates <sbates@...thlin.com>,
Dan Williams <dan.j.williams@...el.com>,
Christian König <christian.koenig@....com>,
John Hubbard <jhubbard@...dia.com>,
Don Dutile <ddutile@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Minturn Dave B <dave.b.minturn@...el.com>,
Jason Ekstrand <jason@...kstrand.net>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Xiong Jianxin <jianxin.xiong@...el.com>,
Bjorn Helgaas <helgaas@...nel.org>,
Ira Weiny <ira.weiny@...el.com>,
Robin Murphy <robin.murphy@....com>,
Martin Oliveira <martin.oliveira@...eticom.com>,
Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
Ralph Campbell <rcampbell@...dia.com>,
Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()
On 2022-07-05 11:21, Greg Kroah-Hartman wrote:
> On Tue, Jul 05, 2022 at 06:50:39PM +0200, Christoph Hellwig wrote:
>> [note for the newcomers, this is about allowing mmap()ing the PCIe
>> P2P memory from the generic PCI P2P code through sysfs, and more
>> importantly how to revoke it on device removal]
>
> We allow mmap on PCIe config space today, right? Why is this different
> from what pci_create_legacy_files() does today?
>
>> On Tue, Jul 05, 2022 at 10:44:49AM -0600, Logan Gunthorpe wrote:
>>> We might be able to. I'm not sure. I'll have to figure out how to find
>>> that inode from the p2pdma code. I haven't found an obvious interface to
>>> do that.
>>
>> I think the right way to approach this would be a new sysfs API
>> that internally calls unmap_mapping_range internally instead of
>> exposing the inode. I suspect that might actually be the right thing
>> to do for iomem_inode as well.
>
> Why do we need something new and how is this any different from the PCI
> binary files I mention above? We have supported PCI hotplug for a very
> long time, do the current PCI binary sysfs files not work properly with
> mmap and removing a device?
The P2PDMA code allocates and hands out struct pages to userspace that
are backed with ZONE_DEVICE memory from a device's BAR. This is quite
different from the existing binary files mentioned above which neither
support struct pages nor allocation.
Logan
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