linux-kernel - Re: [PATCH v6 20/21] PCI/P2PDMA: Introduce pci_mmap

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Message-ID: <20220527190307.GG2960187@ziepe.ca>
Date:   Fri, 27 May 2022 16:03:07 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     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>,
        Christoph Hellwig <hch@....de>,
        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>,
        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>,
        Ralph Campbell <rcampbell@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v6 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()

On Fri, May 27, 2022 at 09:35:07AM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2022-05-27 06:55, Jason Gunthorpe wrote:
> > On Thu, Apr 07, 2022 at 09:47:16AM -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);
> >> +
> >> +	/* Ensure no new pages can be allocated in mappings */
> >> +	p2pdma->active = false;
> >> +	synchronize_rcu();
> >> +
> >> +	unmap_mapping_range(p2pdma->inode->i_mapping, 0, 0, 1);
> >> +
> >> +	/*
> >> +	 * On some architectures, TLB flushes are done with call_rcu()
> >> +	 * so to ensure GUP fast is done with the pages, call synchronize_rcu()
> >> +	 * before freeing them.
> >> +	 */
> >> +	synchronize_rcu();
> >> +	pci_p2pdma_free_mappings(p2pdma->inode->i_mapping);
> > 
> > With the series from Felix getting close this should get updated to
> > not set pte_devmap and use proper natural refcounting without any of
> > this stuff.
> 
> Can you send a link? I'm not sure what you are referring to.

IIRC this is the last part:

https://lore.kernel.org/linux-mm/20220524190632.3304-1-alex.sierra@amd.com/

And the earlier bit with Christoph's pieces looks like it might get
merged to v5.19..

The general idea is once pte_devmap is not set then all the
refcounting works the way it should. This is what all new ZONE_DEVICE
users should do..

Jason