On Thu, 22 Aug 2024 11:37:14 -0700
mhkelley58@xxxxxxxxx wrote:
> From: Michael Kelley <mhklinux@xxxxxxxxxxx>
>
> With the addition of swiotlb throttling functionality, storage
> device drivers may want to know whether using the DMA_ATTR_MAY_BLOCK
> attribute is useful. In a CoCo VM or environment where swiotlb=force
> is used, the MAY_BLOCK attribute enables swiotlb throttling. But if
> throttling is not enable or useful, storage device drivers probably
> do not want to set BLK_MQ_F_BLOCKING at the blk-mq request queue level.
>
> Add function dma_recommend_may_block() that indicates whether
> the underlying implementation of the DMA map calls would benefit
> from allowing blocking. If the kernel was built with
> CONFIG_SWIOTLB_THROTTLE, and swiotlb=force is set (on the kernel
> command line or due to being a CoCo VM), this function returns
> true. Otherwise it returns false.
>
> Signed-off-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
LGTM.
Reviewed-by: Petr Tesarik <ptesarik@xxxxxxxx>
Petr T
> ---
> include/linux/dma-mapping.h | 5 +++++
> kernel/dma/direct.c | 6 ++++++
> kernel/dma/direct.h | 1 +
> kernel/dma/mapping.c | 10 ++++++++++
> 4 files changed, 22 insertions(+)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 7b78294813be..ec2edf068218 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -145,6 +145,7 @@ int dma_set_mask(struct device *dev, u64 mask);
> int dma_set_coherent_mask(struct device *dev, u64 mask);
> u64 dma_get_required_mask(struct device *dev);
> bool dma_addressing_limited(struct device *dev);
> +bool dma_recommend_may_block(struct device *dev);
> size_t dma_max_mapping_size(struct device *dev);
> size_t dma_opt_mapping_size(struct device *dev);
> unsigned long dma_get_merge_boundary(struct device *dev);
> @@ -252,6 +253,10 @@ static inline bool dma_addressing_limited(struct device *dev)
> {
> return false;
> }
> +static inline bool dma_recommend_may_block(struct device *dev)
> +{
> + return false;
> +}
> static inline size_t dma_max_mapping_size(struct device *dev)
> {
> return 0;
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 80e03c0838d4..34d14e4ace64 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -649,6 +649,12 @@ bool dma_direct_all_ram_mapped(struct device *dev)
> check_ram_in_range_map);
> }
>
> +bool dma_direct_recommend_may_block(struct device *dev)
> +{
> + return IS_ENABLED(CONFIG_SWIOTLB_THROTTLE) &&
> + is_swiotlb_force_bounce(dev);
> +}
> +
> size_t dma_direct_max_mapping_size(struct device *dev)
> {
> /* If SWIOTLB is active, use its maximum mapping size */
> diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
> index d2c0b7e632fc..63516a540276 100644
> --- a/kernel/dma/direct.h
> +++ b/kernel/dma/direct.h
> @@ -21,6 +21,7 @@ bool dma_direct_need_sync(struct device *dev, dma_addr_t dma_addr);
> int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
> enum dma_data_direction dir, unsigned long attrs);
> bool dma_direct_all_ram_mapped(struct device *dev);
> +bool dma_direct_recommend_may_block(struct device *dev);
> size_t dma_direct_max_mapping_size(struct device *dev);
>
> #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index b1c18058d55f..832982bafd5a 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -858,6 +858,16 @@ bool dma_addressing_limited(struct device *dev)
> }
> EXPORT_SYMBOL_GPL(dma_addressing_limited);
>
> +bool dma_recommend_may_block(struct device *dev)
> +{
> + const struct dma_map_ops *ops = get_dma_ops(dev);
> +
> + if (dma_map_direct(dev, ops))
> + return dma_direct_recommend_may_block(dev);
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(dma_recommend_may_block);
> +
> size_t dma_max_mapping_size(struct device *dev)
> {
> const struct dma_map_ops *ops = get_dma_ops(dev);
