2020-02-24 19:45:42

by Christoph Hellwig

Subject: [PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

This allows the arch code to reset the page tables to cached access when
freeing a dma coherent allocation that was set to uncached using
arch_dma_set_uncached.

Signed-off-by: Christoph Hellwig <[email protected]>
---
arch/Kconfig | 7 +++++++
include/linux/dma-noncoherent.h | 1 +
kernel/dma/direct.c | 2 ++
3 files changed, 10 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 090cfe0c82a7..c26302f90c96 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -255,6 +255,13 @@ config ARCH_HAS_SET_DIRECT_MAP
config ARCH_HAS_DMA_SET_UNCACHED
bool

+#
+# Select if the architectures provides the arch_dma_clear_uncached symbol
+# to undo an in-place page table remap for uncached access.
+#
+config ARCH_HAS_DMA_CLEAR_UNCACHED
+ bool
+
# Select if arch init_task must go in the __init_task_data section
config ARCH_TASK_STRUCT_ON_STACK
bool
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index 1a4039506673..b59f1b6be3e9 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -109,5 +109,6 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
#endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */

void *arch_dma_set_uncached(void *addr, size_t size);
+void arch_dma_clear_uncached(void *addr, size_t size);

#endif /* _LINUX_DMA_NONCOHERENT_H */
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index f01a8191fd59..a8560052a915 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -219,6 +219,8 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,

if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
vunmap(cpu_addr);
+ else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
+ arch_dma_clear_uncached(cpu_addr, size);

dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
}
--
2.24.1

2020-02-24 21:55:03

by Ira Weiny

Subject: Re: [PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

On Mon, Feb 24, 2020 at 11:44:44AM -0800, Christoph Hellwig wrote:
> This allows the arch code to reset the page tables to cached access when
> freeing a dma coherent allocation that was set to uncached using
> arch_dma_set_uncached.
>
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
> arch/Kconfig | 7 +++++++
> include/linux/dma-noncoherent.h | 1 +
> kernel/dma/direct.c | 2 ++
> 3 files changed, 10 insertions(+)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 090cfe0c82a7..c26302f90c96 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -255,6 +255,13 @@ config ARCH_HAS_SET_DIRECT_MAP
> config ARCH_HAS_DMA_SET_UNCACHED
> bool
>
> +#
> +# Select if the architectures provides the arch_dma_clear_uncached symbol
> +# to undo an in-place page table remap for uncached access.
> +#
> +config ARCH_HAS_DMA_CLEAR_UNCACHED
> + bool
> +
> # Select if arch init_task must go in the __init_task_data section
> config ARCH_TASK_STRUCT_ON_STACK
> bool
> diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
> index 1a4039506673..b59f1b6be3e9 100644
> --- a/include/linux/dma-noncoherent.h
> +++ b/include/linux/dma-noncoherent.h
> @@ -109,5 +109,6 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
> #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
>
> void *arch_dma_set_uncached(void *addr, size_t size);
> +void arch_dma_clear_uncached(void *addr, size_t size);
>
> #endif /* _LINUX_DMA_NONCOHERENT_H */
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index f01a8191fd59..a8560052a915 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -219,6 +219,8 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
>
> if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
> vunmap(cpu_addr);
> + else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> + arch_dma_clear_uncached(cpu_addr, size);

Isn't using arch_dma_clear_uncached() before patch 5 going to break
bisectability?

Ira

>
> dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
> }
> --
> 2.24.1
>

2020-02-24 21:57:22

by Christoph Hellwig

Subject: Re: [PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

On Mon, Feb 24, 2020 at 01:53:28PM -0800, Ira Weiny wrote:
> > + else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> > + arch_dma_clear_uncached(cpu_addr, size);
>
> Isn't using arch_dma_clear_uncached() before patch 5 going to break
> bisectability?

Only if ARCH_HAS_DMA_CLEAR_UNCACHED is selected by anything, which
only happens in patch 5.