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s=20200525; h=Subject:In-Reply-To:MIME-Version:Date: Message-ID:From:References:Cc:To:content-disposition; bh=m8eFPt4Ky/TIsfccDRiBKAA6Im8fSHoSL1rWmfMykMo=; b=litugTKON8LXh2E4fNWf+tdFsh q2CsD9IDYGKKVIawn8gamhxRH644MuufqFWDCKKprPoZHtnAsUpBhIfbDLYsRIwcTEv0TojuuQngh 9J3WiaV60JpGFYmjOv2GNCbeGl6swiX0xF3BgMcQ26cgzBguK1z1MH20QdPZRSQUkmZ+cHM0b8weO nMw1zNo5ZDzrtWTjylir56GRiIHipKmvmqBkHqMQTaNXL2ccxzXkV9uRTIH6IoeArfVAH59w8/LqW lQKk+yTetQfXb8ka5Hd5m4l/qqdvdrI67gA7aRHbkH+i+GOkWx0VzhB9jVE/dO+eFCXLyB281bkpf Y9mF4fFg==; Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.92) (envelope-from ) id 1lLq3k-0000KL-25; Mon, 15 Mar 2021 10:27:13 -0600 To: Ira Weiny 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 , Jason Gunthorpe , =?UTF-8?Q?Christian_K=c3=b6nig?= , Ira Weiny , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin References: <20210311233142.7900-1-logang@deltatee.com> <20210311233142.7900-5-logang@deltatee.com> <20210313013856.GA3402637@iweiny-DESK2.sc.intel.com> From: Logan Gunthorpe Message-ID: <7509243d-b605-953b-6941-72876a60d527@deltatee.com> Date: Mon, 15 Mar 2021 10:27:08 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210313013856.GA3402637@iweiny-DESK2.sc.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: jianxin.xiong@intel.com, dave.hansen@linux.intel.com, jason@jlekstrand.net, dave.b.minturn@intel.com, andrzej.jakowski@intel.com, daniel.vetter@ffwll.ch, willy@infradead.org, ddutile@redhat.com, jhubbard@nvidia.com, iweiny@intel.com, christian.koenig@amd.com, jgg@ziepe.ca, 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, ira.weiny@intel.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH v2 04/11] PCI/P2PDMA: Introduce pci_p2pdma_should_map_bus() and pci_p2pdma_bus_offset() 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) X-Stat-Signature: j5oppj9wxg1m17ptg85tk7zupntb5dns X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: CF4E0C033253 Received-SPF: none (deltatee.com>: No applicable sender policy available) receiver=imf22; identity=mailfrom; envelope-from=""; helo=ale.deltatee.com; client-ip=204.191.154.188 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615825649-741572 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021-03-12 6:38 p.m., Ira Weiny wrote: > On Thu, Mar 11, 2021 at 04:31:34PM -0700, Logan Gunthorpe wrote: >> Introduce pci_p2pdma_should_map_bus() which is meant to be called by >> DMA map functions to determine how to map a given p2pdma page. >> >> pci_p2pdma_bus_offset() is also added to allow callers to get the bus >> offset if they need to map the bus address. >> >> Signed-off-by: Logan Gunthorpe >> --- >> drivers/pci/p2pdma.c | 50 ++++++++++++++++++++++++++++++++++++++ >> include/linux/pci-p2pdma.h | 11 +++++++++ >> 2 files changed, 61 insertions(+) >> >> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c >> index 7f6836732bce..66d16b7eb668 100644 >> --- a/drivers/pci/p2pdma.c >> +++ b/drivers/pci/p2pdma.c >> @@ -912,6 +912,56 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg, >> } >> EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs); >> >> +/** >> + * pci_p2pdma_bus_offset - returns the bus offset for a given page >> + * @page: page to get the offset for >> + * >> + * Must be passed a PCI p2pdma page. >> + */ >> +u64 pci_p2pdma_bus_offset(struct page *page) >> +{ >> + struct pci_p2pdma_pagemap *p2p_pgmap = to_p2p_pgmap(page->pgmap); >> + >> + WARN_ON(!is_pci_p2pdma_page(page)); > > Shouldn't this check be before the to_p2p_pgmap() call? The to_p2p_pgmap() call is just doing pointer arithmetic, so strictly speaking it doesn't need to be before. We just can't access p2p_pgmap until it has been checked. > And I've been told not > to introduce WARN_ON's. Should this be? > > if (!is_pci_p2pdma_page(page)) > return -1; In this case the WARN_ON is just to guard against misuse of the function. It should never happen unless a developer changes the code in a way that is incorrect. So I think that's the correct use of WARN_ON. Though I might change it to WARN and return, that seems safer. Logan