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Date: Thu, 9 May 2024 16:11:26 +0100
From: Steven Price <steven.price@....com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>,
Christoph Hellwig <hch@....de>
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
Will Deacon <will@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
Magnus Karlsson <magnus.karlsson@...el.com>,
nex.sw.ncis.osdt.itp.upstreaming@...el.com, bpf@...r.kernel.org,
netdev@...r.kernel.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma: fix DMA sync for drivers not calling dma_set_mask*()
On 09/05/2024 15:46, Alexander Lobakin wrote:
> There are several reports that the DMA sync shortcut broke non-coherent
> devices.
> dev->dma_need_sync is false after the &device allocation and if a driver
> didn't call dma_set_mask*(), it will still be false even if the device
> is not DMA-coherent and thus needs synchronizing. Due to historical
> reasons, there's still a lot of drivers not calling it.
> Invert the boolean, so that the sync will be performed by default and
> the shortcut will be enabled only when calling dma_set_mask*().
>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Closes: https://lore.kernel.org/lkml/46160534-5003-4809-a408-6b3a3f4921e9@samsung.com
> Reported-by: Steven Price <steven.price@....com>
> Closes: https://lore.kernel.org/lkml/010686f5-3049-46a1-8230-7752a1b433ff@arm.com
> Fixes: 32ba8b823252 ("dma: avoid redundant calls for sync operations")
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
Tested-by: Steven Price <steven.price@....com>
Thanks for the quick fix.
Note that the fixes hash (32ba8b823252) is not the one in linux-next -
that's f406c8e4b770. If the branch is getting rebased then no problem, I
just thought I should point that out.
Thanks,
Steve
> ---
> include/linux/device.h | 4 ++--
> include/linux/dma-map-ops.h | 4 ++--
> include/linux/dma-mapping.h | 2 +-
> kernel/dma/mapping.c | 10 +++++-----
> kernel/dma/swiotlb.c | 2 +-
> 5 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index ed95b829f05b..d4b50accff26 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -691,7 +691,7 @@ struct device_physical_location {
> * and optionall (if the coherent mask is large enough) also
> * for dma allocations. This flag is managed by the dma ops
> * instance from ->dma_supported.
> - * @dma_need_sync: The device needs performing DMA sync operations.
> + * @dma_skip_sync: DMA sync operations can be skipped for coherent buffers.
> *
> * At the lowest level, every device in a Linux system is represented by an
> * instance of struct device. The device structure contains the information
> @@ -805,7 +805,7 @@ struct device {
> bool dma_ops_bypass : 1;
> #endif
> #ifdef CONFIG_DMA_NEED_SYNC
> - bool dma_need_sync:1;
> + bool dma_skip_sync:1;
> #endif
> };
>
> diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
> index 4893cb89cb52..5217b922d29f 100644
> --- a/include/linux/dma-map-ops.h
> +++ b/include/linux/dma-map-ops.h
> @@ -280,8 +280,8 @@ static inline void dma_reset_need_sync(struct device *dev)
> {
> #ifdef CONFIG_DMA_NEED_SYNC
> /* Reset it only once so that the function can be called on hotpath */
> - if (unlikely(!dev->dma_need_sync))
> - dev->dma_need_sync = true;
> + if (unlikely(dev->dma_skip_sync))
> + dev->dma_skip_sync = false;
> #endif
> }
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index eb4e15893b6c..f693aafe221f 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -295,7 +295,7 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr);
> static inline bool dma_dev_need_sync(const struct device *dev)
> {
> /* Always call DMA sync operations when debugging is enabled */
> - return dev->dma_need_sync || IS_ENABLED(CONFIG_DMA_API_DEBUG);
> + return !dev->dma_skip_sync || IS_ENABLED(CONFIG_DMA_API_DEBUG);
> }
>
> static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 3524bc92c37f..3f77c3f8d16d 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -392,7 +392,7 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
>
> if (dma_map_direct(dev, ops))
> /*
> - * dma_need_sync could've been reset on first SWIOTLB buffer
> + * dma_skip_sync could've been reset on first SWIOTLB buffer
> * mapping, but @dma_addr is not necessary an SWIOTLB buffer.
> * In this case, fall back to more granular check.
> */
> @@ -407,20 +407,20 @@ static void dma_setup_need_sync(struct device *dev)
>
> if (dma_map_direct(dev, ops) || (ops->flags & DMA_F_CAN_SKIP_SYNC))
> /*
> - * dma_need_sync will be reset to %true on first SWIOTLB buffer
> + * dma_skip_sync will be reset to %false on first SWIOTLB buffer
> * mapping, if any. During the device initialization, it's
> * enough to check only for the DMA coherence.
> */
> - dev->dma_need_sync = !dev_is_dma_coherent(dev);
> + dev->dma_skip_sync = dev_is_dma_coherent(dev);
> else if (!ops->sync_single_for_device && !ops->sync_single_for_cpu &&
> !ops->sync_sg_for_device && !ops->sync_sg_for_cpu)
> /*
> * Synchronization is not possible when none of DMA sync ops
> * is set.
> */
> - dev->dma_need_sync = false;
> + dev->dma_skip_sync = true;
> else
> - dev->dma_need_sync = true;
> + dev->dma_skip_sync = false;
> }
> #else /* !CONFIG_DMA_NEED_SYNC */
> static inline void dma_setup_need_sync(struct device *dev) { }
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index ae3e593eaadb..068134697cf1 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -1409,7 +1409,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
> }
>
> /*
> - * If dma_need_sync wasn't set, reset it on first SWIOTLB buffer
> + * If dma_skip_sync was set, reset it on first SWIOTLB buffer
> * mapping to always sync SWIOTLB buffers.
> */
> dma_reset_need_sync(dev);
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