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Date:   Tue, 28 Sep 2021 17:05:06 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
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        Stephen Bates <sbates@raithlin.com>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Don Dutile <ddutile@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jakowski Andrzej <andrzej.jakowski@intel.com>,
        Minturn Dave B <dave.b.minturn@intel.com>,
        Jason Ekstrand <jason@jlekstrand.net>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Xiong Jianxin <jianxin.xiong@intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Martin Oliveira <martin.oliveira@eideticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Subject: Re: [PATCH v3 19/20] PCI/P2PDMA: introduce pci_mmap_p2pmem()
Message-ID: <20210928200506.GX3544071@ziepe.ca>
References: <20210916234100.122368-1-logang@deltatee.com>
 <20210916234100.122368-20-logang@deltatee.com>
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On Thu, Sep 16, 2021 at 05:40:59PM -0600, Logan Gunthorpe wrote:

> +static void pci_p2pdma_unmap_mappings(void *data)
> +{
> +	struct pci_dev *pdev = data;
> +	struct pci_p2pdma *p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
> +
> +	p2pdma->active = false;
> +	synchronize_rcu();
> +	unmap_mapping_range(p2pdma->inode->i_mapping, 0, 0, 1);
> +	pci_p2pdma_free_mappings(p2pdma->inode->i_mapping);
> +}

If this is going to rely on unmap_mapping_range then GUP should also
reject this memory for FOLL_LONGTERM..

What along this control flow:

> +       error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_unmap_mappings,
> +                                        pdev);

Waits for all the page refcounts to go to zero?

Jason