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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,
	linux-mm@kvack.org, iommu@lists.linux-foundation.org,
	"Stephen Bates" <sbates@raithlin.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Christian König" <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()
Date: Wed, 29 Sep 2021 21:36:52 -0300	[thread overview]
Message-ID: <20210930003652.GH3544071@ziepe.ca> (raw)
In-Reply-To: <f9a83402-3d66-7437-ca47-77bac4108424@deltatee.com>

On Wed, Sep 29, 2021 at 05:49:36PM -0600, Logan Gunthorpe wrote:

> Some of this seems out of date. Pretty sure the pages are not refcounted
> with vmf_insert_mixed() and vmf_insert_mixed() is currently the only way
> to use VM_MIXEDMAP mappings.

Hum.

vmf_insert_mixed() boils down to insert_pfn() which always sets the
special bit, so vm_normal_page() returns NULL and thus the pages are
not freed during zap.

So, if the pages are always special and not refcounted all the docs
seem really out of date - or rather they describe the situation
without the special bit, I think.

Why would DAX want to do this in the first place?? This means the
address space zap is much more important that just speeding up
destruction, it is essential for correctness since the PTEs are not
holding refcounts naturally...

Sigh.

Jason

  reply	other threads:[~2021-09-30  0:36 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-16 23:40 [PATCH v3 00/20] Userspace P2PDMA with O_DIRECT NVMe devices Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 01/20] lib/scatterlist: add flag for indicating P2PDMA segments in an SGL Logan Gunthorpe
2021-09-28 18:32   ` Jason Gunthorpe
2021-09-29 21:15     ` Logan Gunthorpe
2021-09-30  4:47   ` Chaitanya Kulkarni
2021-09-30 16:49     ` Logan Gunthorpe
2021-09-30  4:57   ` Chaitanya Kulkarni
2021-09-16 23:40 ` [PATCH v3 02/20] PCI/P2PDMA: attempt to set map_type if it has not been set Logan Gunthorpe
2021-09-27 18:50   ` Bjorn Helgaas
2021-09-16 23:40 ` [PATCH v3 03/20] PCI/P2PDMA: make pci_p2pdma_map_type() non-static Logan Gunthorpe
2021-09-27 18:46   ` Bjorn Helgaas
2021-09-28 18:48   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations Logan Gunthorpe
2021-09-27 18:53   ` Bjorn Helgaas
2021-09-27 19:59     ` Logan Gunthorpe
2021-09-28 18:55   ` Jason Gunthorpe
2021-09-29 21:26     ` Logan Gunthorpe
2021-09-28 22:05   ` [PATCH v3 4/20] " Jason Gunthorpe
2021-09-29 21:30     ` Logan Gunthorpe
2021-09-29 22:46       ` Jason Gunthorpe
2021-09-29 23:00         ` Logan Gunthorpe
2021-09-29 23:40           ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 05/20] dma-mapping: allow EREMOTEIO return code for P2PDMA transfers Logan Gunthorpe
2021-09-28 18:57   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 06/20] dma-direct: support PCI P2PDMA pages in dma-direct map_sg Logan Gunthorpe
2021-09-28 19:08   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 07/20] dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support Logan Gunthorpe
2021-09-28 19:11   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 08/20] iommu/dma: support PCI P2PDMA pages in dma-iommu map_sg Logan Gunthorpe
2021-09-28 19:15   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 09/20] nvme-pci: check DMA ops when indicating support for PCI P2PDMA Logan Gunthorpe
2021-09-30  5:06   ` Chaitanya Kulkarni
2021-09-30 16:51     ` Logan Gunthorpe
2021-09-30 17:19       ` Chaitanya Kulkarni
2021-09-16 23:40 ` [PATCH v3 10/20] nvme-pci: convert to using dma_map_sgtable() Logan Gunthorpe
2021-10-05 22:29   ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 11/20] RDMA/core: introduce ib_dma_pci_p2p_dma_supported() Logan Gunthorpe
2021-09-28 19:17   ` Jason Gunthorpe
2021-10-05 22:31   ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 12/20] RDMA/rw: use dma_map_sgtable() Logan Gunthorpe
2021-09-28 19:43   ` Jason Gunthorpe
2021-09-29 22:56     ` Logan Gunthorpe
2021-10-05 22:40     ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 13/20] PCI/P2PDMA: remove pci_p2pdma_[un]map_sg() Logan Gunthorpe
2021-09-27 18:50   ` Bjorn Helgaas
2021-09-28 19:43   ` Jason Gunthorpe
2021-10-05 22:42   ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 14/20] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages Logan Gunthorpe
2021-09-28 19:47   ` Jason Gunthorpe
2021-09-29 21:34     ` Logan Gunthorpe
2021-09-29 22:48       ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 15/20] iov_iter: introduce iov_iter_get_pages_[alloc_]flags() Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 16/20] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages() Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 17/20] block: set FOLL_PCI_P2PDMA in bio_map_user_iov() Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 18/20] mm: use custom page_free for P2PDMA pages Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 19/20] PCI/P2PDMA: introduce pci_mmap_p2pmem() Logan Gunthorpe
2021-09-27 18:49   ` Bjorn Helgaas
2021-09-28 19:55   ` Jason Gunthorpe
2021-09-29 21:42     ` Logan Gunthorpe
2021-09-29 23:05       ` Jason Gunthorpe
2021-09-29 23:27         ` Logan Gunthorpe
2021-09-29 23:35           ` Jason Gunthorpe
2021-09-29 23:49             ` Logan Gunthorpe
2021-09-30  0:36               ` Jason Gunthorpe [this message]
2021-10-01 13:48                 ` Jason Gunthorpe
2021-10-01 17:01                   ` Logan Gunthorpe
2021-10-01 17:45                     ` Jason Gunthorpe
2021-10-01 20:13                       ` Logan Gunthorpe
2021-10-01 22:14                         ` Jason Gunthorpe
2021-10-01 22:22                           ` Logan Gunthorpe
2021-10-01 22:46                             ` Jason Gunthorpe
2021-10-01 23:27                               ` John Hubbard
2021-10-01 23:34                               ` Logan Gunthorpe
2021-10-04  6:58                       ` Christian König
2021-10-04 13:11                         ` Jason Gunthorpe
2021-10-04 13:22                           ` Christian König
2021-10-04 13:27                             ` Jason Gunthorpe
2021-10-04 14:54                               ` Christian König
2021-09-28 20:05   ` Jason Gunthorpe
2021-09-29 21:46     ` Logan Gunthorpe
2021-09-16 23:41 ` [PATCH v3 20/20] nvme-pci: allow mmaping the CMB in userspace Logan Gunthorpe
2021-09-28 20:02 ` [PATCH v3 00/20] Userspace P2PDMA with O_DIRECT NVMe devices Jason Gunthorpe
2021-09-29 21:50   ` Logan Gunthorpe
2021-09-29 23:21     ` Jason Gunthorpe
2021-09-29 23:28       ` Logan Gunthorpe
2021-09-29 23:36         ` Jason Gunthorpe
2021-09-29 23:52           ` Logan Gunthorpe

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