[PATCH] powerpc/dma: Fix invalid DMA mmap behavior

[Alexey Kardashevskiy]

On 18/07/2019 09:54, Shawn Anastasio wrote:
> The refactor of powerpc DMA functions in commit 6666cc17d780
> ("powerpc/dma: remove dma_nommu_mmap_coherent") incorrectly
> changes the way DMA mappings are handled on powerpc.
> Since this change, all mapped pages are marked as cache-inhibited
> through the default implementation of arch_dma_mmap_pgprot.
> This differs from the previous behavior of only marking pages
> in noncoherent mappings as cache-inhibited and has resulted in
> sporadic system crashes in certain hardware configurations and
> workloads (see Bugzilla).
> 
> This commit restores the previous correct behavior by providing
> an implementation of arch_dma_mmap_pgprot that only marks
> pages in noncoherent mappings as cache-inhibited. As this behavior
> should be universal for all powerpc platforms a new file,
> dma-generic.c, was created to store it.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204145
> Fixes: 6666cc17d780 ("powerpc/dma: remove dma_nommu_mmap_coherent")
> Signed-off-by: Shawn Anastasio <shawn at anastas.io>


Is this the default one?

include/linux/dma-noncoherent.h
# define arch_dma_mmap_pgprot(dev, prot, attrs) pgprot_noncached(prot)

Out of curiosity - do not we want to fix this one for everyone?

Either way, the patch is correct. I'm glad to know it was not my " 
powerpc/ioda2: Yet another attempt to allow DMA masks between 32 and 59" 
which broke it :)

Reviewed-by: Alexey Kardashevskiy <aik at ozlabs.ru>



> ---
>   arch/powerpc/Kconfig             |  1 +
>   arch/powerpc/kernel/Makefile     |  3 ++-
>   arch/powerpc/kernel/dma-common.c | 17 +++++++++++++++++
>   3 files changed, 20 insertions(+), 1 deletion(-)
>   create mode 100644 arch/powerpc/kernel/dma-common.c
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index d8dcd8820369..77f6ebf97113 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -121,6 +121,7 @@ config PPC
>   	select ARCH_32BIT_OFF_T if PPC32
>   	select ARCH_HAS_DEBUG_VIRTUAL
>   	select ARCH_HAS_DEVMEM_IS_ALLOWED
> +	select ARCH_HAS_DMA_MMAP_PGPROT
>   	select ARCH_HAS_ELF_RANDOMIZE
>   	select ARCH_HAS_FORTIFY_SOURCE
>   	select ARCH_HAS_GCOV_PROFILE_ALL
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 56dfa7a2a6f2..ea0c69236789 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -49,7 +49,8 @@ obj-y				:= cputable.o ptrace.o syscalls.o \
>   				   signal.o sysfs.o cacheinfo.o time.o \
>   				   prom.o traps.o setup-common.o \
>   				   udbg.o misc.o io.o misc_$(BITS).o \
> -				   of_platform.o prom_parse.o
> +				   of_platform.o prom_parse.o \
> +				   dma-common.o
>   obj-$(CONFIG_PPC64)		+= setup_64.o sys_ppc32.o \
>   				   signal_64.o ptrace32.o \
>   				   paca.o nvram_64.o firmware.o
> diff --git a/arch/powerpc/kernel/dma-common.c b/arch/powerpc/kernel/dma-common.c
> new file mode 100644
> index 000000000000..5a15f99f4199
> --- /dev/null
> +++ b/arch/powerpc/kernel/dma-common.c
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Contains common dma routines for all powerpc platforms.
> + *
> + * Copyright (C) 2019 Shawn Anastasio (shawn at anastas.io)
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/dma-noncoherent.h>
> +
> +pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
> +		unsigned long attrs)
> +{
> +	if (!dev_is_dma_coherent(dev))
> +		return pgprot_noncached(prot);
> +	return prot;
> +}
> 

-- 
Alexey