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Received: from s01060023bee90a7d.cg.shawcable.net ([24.64.145.4] helo=[192.168.0.10]) by ale.deltatee.com with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1kb5vm-0003Mq-D0; Fri, 06 Nov 2020 10:53:47 -0700 To: Jason Gunthorpe 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 , Christoph Hellwig , Dan Williams , =?UTF-8?Q?Christian_K=c3=b6nig?= , Ira Weiny , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter References: <20201106170036.18713-1-logang@deltatee.com> <20201106170036.18713-15-logang@deltatee.com> <20201106172206.GS36674@ziepe.ca> <20201106174223.GU36674@ziepe.ca> From: Logan Gunthorpe Message-ID: <2c2d2815-165e-2ef9-60d6-3ace7ff3aaa5@deltatee.com> Date: Fri, 6 Nov 2020 10:53:45 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201106174223.GU36674@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 24.64.145.4 X-SA-Exim-Rcpt-To: daniel.vetter@ffwll.ch, willy@infradead.org, ddutile@redhat.com, jhubbard@nvidia.com, iweiny@intel.com, christian.koenig@amd.com, dan.j.williams@intel.com, hch@lst.de, sbates@raithlin.com, iommu@lists.linux-foundation.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH 14/15] PCI/P2PDMA: Introduce pci_mmap_p2pmem() X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-11-06 10:42 a.m., Jason Gunthorpe wrote: > On Fri, Nov 06, 2020 at 10:28:00AM -0700, Logan Gunthorpe wrote: >> >> >> On 2020-11-06 10:22 a.m., Jason Gunthorpe wrote: >>> On Fri, Nov 06, 2020 at 10:00:35AM -0700, Logan Gunthorpe wrote: >>>> Introduce pci_mmap_p2pmem() which is a helper to allocate and mmap >>>> a hunk of p2pmem into userspace. >>>> >>>> Signed-off-by: Logan Gunthorpe >>>> drivers/pci/p2pdma.c | 104 +++++++++++++++++++++++++++++++++++++ >>>> include/linux/pci-p2pdma.h | 6 +++ >>>> 2 files changed, 110 insertions(+) >>>> >>>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c >>>> index 9961e779f430..8eab53ac59ae 100644 >>>> +++ b/drivers/pci/p2pdma.c >>>> @@ -16,6 +16,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> #include >>>> #include >>>> #include >>>> @@ -1055,3 +1056,106 @@ ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev, >>>> return sprintf(page, "%s\n", pci_name(p2p_dev)); >>>> } >>>> EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show); >>>> + >>>> +struct pci_p2pdma_map { >>>> + struct kref ref; >>>> + struct pci_dev *pdev; >>>> + void *kaddr; >>>> + size_t len; >>>> +}; >>> >>> Why have this at all? Nothing uses it and no vm_operations ops are >>> implemented? >> >> It's necessary to free the allocated p2pmem when the mapping is torn down. > > That's suspicious.. Once in a VMA the lifetime of the page must be > controlled by the page refcount, it can't be put back into the genpool > just because the vma was destroed. Ah, hmm, yes. I guess the pages have to be hooked and returned to the genalloc through free_devmap_managed_page(). Seems like it might be doable... but it will complicate things for users that don't want to use the genpool (though no such users exist upstream). Logan