linux-kernel - Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap

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Date:   Tue, 5 Jul 2022 10:44:49 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     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 10:43, Christoph Hellwig wrote:
> On Tue, Jul 05, 2022 at 10:41:52AM -0600, Logan Gunthorpe wrote:
>> Using sysfs means we don't need all the messy callbacks from the nvme
>> driver, which is a plus. But I'm not sure how we'd get or unmap the
>> mapping of a sysfs file or avoid the anonymous inode. Seems with the
>> existing PCI resources, it uses an bin_attribute->f_mapping() callback
>> to pass back the iomem_get_mapping() mapping on file open.
>> revoke_iomem() is then used to nuke the VMAs. I don't think we can use
>> the same infrastructure here as that would add a dependency on
>> CONFIG_IO_STRICT_DEVMEM; which would be odd. And I'm not sure whether
>> there is a better way.
> 
> Why can't we do the revoke on the actual sysfs inode?

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.

Logan