linux-kernel - Re: [PATCH v3 19/20] PCI/P2PDMA: introduce pci_mmap

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Message-ID: <20211004132759.GX3544071@ziepe.ca>
Date:   Mon, 4 Oct 2021 10:27:59 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christian König <christian.koenig@....com>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Alistair Popple <apopple@...dia.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        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>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        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>
Subject: Re: [PATCH v3 19/20] PCI/P2PDMA: introduce pci_mmap_p2pmem()

On Mon, Oct 04, 2021 at 03:22:22PM +0200, Christian König wrote:

> That use case is completely unrelated to GUP and when this doesn't work we
> have quite a problem.

My read is that unmap_mapping_range() guarentees the physical TLB
hardware is serialized across all CPUs upon return.

It also guarentees GUP slow is serialized due to the page table
spinlocks.

Jason