From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2DA3C433EF for ; Mon, 4 Jul 2022 15:08:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 200136B0072; Mon, 4 Jul 2022 11:08:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1AE736B0073; Mon, 4 Jul 2022 11:08:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 077DC6B0074; Mon, 4 Jul 2022 11:08:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id ED6B06B0072 for ; Mon, 4 Jul 2022 11:08:47 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id C623D2082D for ; Mon, 4 Jul 2022 15:08:47 +0000 (UTC) X-FDA: 79649749494.06.4E1A0A9 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf30.hostedemail.com (Postfix) with ESMTP id DFD3B80021 for ; Mon, 4 Jul 2022 15:08:46 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 03A6F23A; Mon, 4 Jul 2022 08:08:46 -0700 (PDT) Received: from [10.57.86.91] (unknown [10.57.86.91]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B9C583F792; Mon, 4 Jul 2022 08:08:41 -0700 (PDT) Message-ID: <2be62742-4737-bb3c-5467-011a26edfcea@arm.com> Date: Mon, 4 Jul 2022 16:08:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v7 01/21] lib/scatterlist: add flag for indicating P2PDMA segments in an SGL Content-Language: en-GB To: Logan Gunthorpe , 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 Cc: Stephen Bates , Christoph Hellwig , Dan Williams , Jason Gunthorpe , =?UTF-8?Q?Christian_K=c3=b6nig?= , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Martin Oliveira , Chaitanya Kulkarni , Ralph Campbell , Chaitanya Kulkarni References: <20220615161233.17527-1-logang@deltatee.com> <20220615161233.17527-2-logang@deltatee.com> From: Robin Murphy In-Reply-To: <20220615161233.17527-2-logang@deltatee.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656947327; a=rsa-sha256; cv=none; b=Q4Jlr8o9Kv1rSSaKKGMSDnlVPnQyn1z3ecp0wOFYtxyKHT3fQAuEvHmfrJMmUgxGzT1Z2e nLIcRR4bFr3TJJ9wk/cv3LlW1HD66AvTvkkxnJ50XU36taOrVniMwaRz6+Bpqd3ZY6TxEL yv8Eg4U6zenYIxZOEy0VtePs6QVsg1k= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; spf=pass (imf30.hostedemail.com: domain of robin.murphy@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=robin.murphy@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656947327; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gzMIizqjvcjUqAnb5IAJ862AQ/s/fxwCGoKaF18Q1o0=; b=y12uNz56YV30mti+L4pJ1+ENwdYeVZE0AZq30L/srsJRo5BRhxNe9G/NPGgh+kYgBGOt2g EHhy4Z7fg+K/5aqUQbI2f1LP5SqfpOGMdag+Vfa8bUTcVdT7quUsLOV9oQAix6GDSXZTbX +q/fdALpgiNdR7pTLbEYhOGpMnrvkBk= X-Stat-Signature: hsw6gi8ynp8dpws18hqddrn8oqk6m965 X-Rspamd-Queue-Id: DFD3B80021 Authentication-Results: imf30.hostedemail.com; dkim=none; spf=pass (imf30.hostedemail.com: domain of robin.murphy@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=robin.murphy@arm.com; dmarc=pass (policy=none) header.from=arm.com X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1656947326-405407 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 2022-06-15 17:12, Logan Gunthorpe wrote: > Make use of the third free LSB in scatterlist's page_link on 64bit systems. > > The extra bit will be used by dma_[un]map_sg_p2pdma() to determine when a > given SGL segments dma_address points to a PCI bus address. > dma_unmap_sg_p2pdma() will need to perform different cleanup when a > segment is marked as a bus address. > > The new bit will only be used when CONFIG_PCI_P2PDMA is set; this means > PCI P2PDMA will require CONFIG_64BIT. This should be acceptable as the > majority of P2PDMA use cases are restricted to newer root complexes and > roughly require the extra address space for memory BARs used in the > transactions. Another thought that's hit me slightly late; depending on CONFIG_64BIT also means that we've got a whole 4 bytes of padding in struct scatterlist to play with, so at that point maybe it's worth considering carrying new extra DMA mapping properties in their own field(s). For instance it would also be really helpful to flag whether a segment is bounce-buffered or not. Robin. > Signed-off-by: Logan Gunthorpe > Reviewed-by: Chaitanya Kulkarni > --- > drivers/pci/Kconfig | 5 +++++ > include/linux/scatterlist.h | 44 ++++++++++++++++++++++++++++++++++++- > 2 files changed, 48 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig > index 133c73207782..5cc7cba1941f 100644 > --- a/drivers/pci/Kconfig > +++ b/drivers/pci/Kconfig > @@ -164,6 +164,11 @@ config PCI_PASID > config PCI_P2PDMA > bool "PCI peer-to-peer transfer support" > depends on ZONE_DEVICE > + # > + # The need for the scatterlist DMA bus address flag means PCI P2PDMA > + # requires 64bit > + # > + depends on 64BIT > select GENERIC_ALLOCATOR > help > Enableѕ drivers to do PCI peer-to-peer transactions to and from > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 7ff9d6386c12..6561ca8aead8 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -64,12 +64,24 @@ struct sg_append_table { > #define SG_CHAIN 0x01UL > #define SG_END 0x02UL > > +/* > + * bit 2 is the third free bit in the page_link on 64bit systems which > + * is used by dma_unmap_sg() to determine if the dma_address is a > + * bus address when doing P2PDMA. > + */ > +#ifdef CONFIG_PCI_P2PDMA > +#define SG_DMA_BUS_ADDRESS 0x04UL > +static_assert(__alignof__(struct page) >= 8); > +#else > +#define SG_DMA_BUS_ADDRESS 0x00UL > +#endif > + > /* > * We overload the LSB of the page pointer to indicate whether it's > * a valid sg entry, or whether it points to the start of a new scatterlist. > * Those low bits are there for everyone! (thanks mason :-) > */ > -#define SG_PAGE_LINK_MASK (SG_CHAIN | SG_END) > +#define SG_PAGE_LINK_MASK (SG_CHAIN | SG_END | SG_DMA_BUS_ADDRESS) > > static inline unsigned int __sg_flags(struct scatterlist *sg) > { > @@ -91,6 +103,11 @@ static inline bool sg_is_last(struct scatterlist *sg) > return __sg_flags(sg) & SG_END; > } > > +static inline bool sg_is_dma_bus_address(struct scatterlist *sg) > +{ > + return __sg_flags(sg) & SG_DMA_BUS_ADDRESS; > +} > + > /** > * sg_assign_page - Assign a given page to an SG entry > * @sg: SG entry > @@ -245,6 +262,31 @@ static inline void sg_unmark_end(struct scatterlist *sg) > sg->page_link &= ~SG_END; > } > > +/** > + * sg_dma_mark_bus address - Mark the scatterlist entry as a bus address > + * @sg: SG entryScatterlist > + * > + * Description: > + * Marks the passed in sg entry to indicate that the dma_address is > + * a bus address and doesn't need to be unmapped. > + **/ > +static inline void sg_dma_mark_bus_address(struct scatterlist *sg) > +{ > + sg->page_link |= SG_DMA_BUS_ADDRESS; > +} > + > +/** > + * sg_unmark_pci_p2pdma - Unmark the scatterlist entry as a bus address > + * @sg: SG entryScatterlist > + * > + * Description: > + * Clears the bus address mark. > + **/ > +static inline void sg_dma_unmark_bus_address(struct scatterlist *sg) > +{ > + sg->page_link &= ~SG_DMA_BUS_ADDRESS; > +} > + > /** > * sg_phys - Return physical address of an sg entry > * @sg: SG entry