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Tue, 11 May 2021 16:06:01 +0000 (UTC) Received: from [10.3.115.19] (ovpn-115-19.phx2.redhat.com [10.3.115.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0FBB95C232; Tue, 11 May 2021 16:05:56 +0000 (UTC) Subject: Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma() 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 , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy References: <20210408170123.8788-1-logang@deltatee.com> <20210408170123.8788-6-logang@deltatee.com> From: Don Dutile Message-ID: Date: Tue, 11 May 2021 12:05:56 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20210408170123.8788-6-logang@deltatee.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Rspamd-Queue-Id: EFA52500153D Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=bpzbCL2g; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf01.hostedemail.com: domain of ddutile@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=ddutile@redhat.com X-Rspamd-Server: rspam03 X-Stat-Signature: iuo7wm1ket1zpe3dffem19ycnc3g463y Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620749166-435169 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 4/8/21 1:01 PM, Logan Gunthorpe wrote: > dma_map_sg() either returns a positive number indicating the number > of entries mapped or zero indicating that resources were not available > to create the mapping. When zero is returned, it is always safe to retry > the mapping later once resources have been freed. > > Once P2PDMA pages are mixed into the SGL there may be pages that may > never be successfully mapped with a given device because that device may > not actually be able to access those pages. Thus, multiple error > conditions will need to be distinguished to determine weather a retry s/weather/whether/ > is safe. > > Introduce dma_map_sg_p2pdma[_attrs]() with a different calling > convention from dma_map_sg(). The function will return a positive > integer on success or a negative errno on failure. > > ENOMEM will be used to indicate a resource failure and EREMOTEIO to > indicate that a P2PDMA page is not mappable. > > The __DMA_ATTR_PCI_P2PDMA attribute is introduced to inform the lower > level implementations that P2PDMA pages are allowed and to warn if a > caller introduces them into the regular dma_map_sg() interface. > > Signed-off-by: Logan Gunthorpe John caught any other comment I had (and more). -dd > --- > include/linux/dma-mapping.h | 15 +++++++++++ > kernel/dma/mapping.c | 52 ++++++++++++++++++++++++++++++++----- > 2 files changed, 61 insertions(+), 6 deletions(-) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 2a984cb4d1e0..50b8f586cf59 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -60,6 +60,12 @@ > * at least read-only at lesser-privileged levels). > */ > #define DMA_ATTR_PRIVILEGED (1UL << 9) > +/* > + * __DMA_ATTR_PCI_P2PDMA: This should not be used directly, use > + * dma_map_sg_p2pdma() instead. Used internally to indicate that the > + * caller is using the dma_map_sg_p2pdma() interface. > + */ > +#define __DMA_ATTR_PCI_P2PDMA (1UL << 10) > > /* > * A dma_addr_t can hold any valid DMA or bus address for the platform. It can > @@ -107,6 +113,8 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size, > enum dma_data_direction dir, unsigned long attrs); > int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > enum dma_data_direction dir, unsigned long attrs); > +int dma_map_sg_p2pdma_attrs(struct device *dev, struct scatterlist *sg, > + int nents, enum dma_data_direction dir, unsigned long attrs); > void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg, > int nents, enum dma_data_direction dir, > unsigned long attrs); > @@ -160,6 +168,12 @@ static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, > { > return 0; > } > +static inline int dma_map_sg_p2pdma_attrs(struct device *dev, > + struct scatterlist *sg, int nents, enum dma_data_direction dir, > + unsigned long attrs) > +{ > + return 0; > +} > static inline void dma_unmap_sg_attrs(struct device *dev, > struct scatterlist *sg, int nents, enum dma_data_direction dir, > unsigned long attrs) > @@ -392,6 +406,7 @@ static inline void dma_sync_sgtable_for_device(struct device *dev, > #define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, 0) > #define dma_unmap_single(d, a, s, r) dma_unmap_single_attrs(d, a, s, r, 0) > #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0) > +#define dma_map_sg_p2pdma(d, s, n, r) dma_map_sg_p2pdma_attrs(d, s, n, r, 0) > #define dma_unmap_sg(d, s, n, r) dma_unmap_sg_attrs(d, s, n, r, 0) > #define dma_map_page(d, p, o, s, r) dma_map_page_attrs(d, p, o, s, r, 0) > #define dma_unmap_page(d, a, s, r) dma_unmap_page_attrs(d, a, s, r, 0) > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c > index b6a633679933..923089c4267b 100644 > --- a/kernel/dma/mapping.c > +++ b/kernel/dma/mapping.c > @@ -177,12 +177,8 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size, > } > EXPORT_SYMBOL(dma_unmap_page_attrs); > > -/* > - * dma_maps_sg_attrs returns 0 on error and > 0 on success. > - * It should never return a value < 0. > - */ > -int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > - enum dma_data_direction dir, unsigned long attrs) > +static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, > + int nents, enum dma_data_direction dir, unsigned long attrs) > { > const struct dma_map_ops *ops = get_dma_ops(dev); > int ents; > @@ -197,6 +193,20 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > ents = dma_direct_map_sg(dev, sg, nents, dir, attrs); > else > ents = ops->map_sg(dev, sg, nents, dir, attrs); > + > + return ents; > +} > + > +/* > + * dma_maps_sg_attrs returns 0 on error and > 0 on success. > + * It should never return a value < 0. > + */ > +int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > + enum dma_data_direction dir, unsigned long attrs) > +{ > + int ents; > + > + ents = __dma_map_sg_attrs(dev, sg, nents, dir, attrs); > BUG_ON(ents < 0); > debug_dma_map_sg(dev, sg, nents, ents, dir); > > @@ -204,6 +214,36 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, > } > EXPORT_SYMBOL(dma_map_sg_attrs); > > +/* > + * like dma_map_sg_attrs, but returns a negative errno on error (and > 0 > + * on success). This function must be used if PCI P2PDMA pages might > + * be in the scatterlist. > + * > + * On error this function may return: > + * -ENOMEM indicating that there was not enough resources available and > + * the transfer may be retried later > + * -EREMOTEIO indicating that P2PDMA pages were included but cannot > + * be mapped by the specified device, retries will always fail > + * > + * The scatterlist should be unmapped with the regular dma_unmap_sg[_attrs](). > + */ > +int dma_map_sg_p2pdma_attrs(struct device *dev, struct scatterlist *sg, > + int nents, enum dma_data_direction dir, unsigned long attrs) > +{ > + int ents; > + > + ents = __dma_map_sg_attrs(dev, sg, nents, dir, > + attrs | __DMA_ATTR_PCI_P2PDMA); > + if (!ents) > + ents = -ENOMEM; > + > + if (ents > 0) > + debug_dma_map_sg(dev, sg, nents, ents, dir); > + > + return ents; > +} > +EXPORT_SYMBOL_GPL(dma_map_sg_p2pdma_attrs); > + > void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg, > int nents, enum dma_data_direction dir, > unsigned long attrs)