On 7/17/19 9:59 PM, Alexey Kardashevskiy wrote:
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 <sh...@anastas.io>
Is this the default one?
include/linux/dma-noncoherent.h
# define arch_dma_mmap_pgprot(dev, prot, attrs) pgprot_noncached(prot)
Yep, that's the one.
Out of curiosity - do not we want to fix this one for everyone?
Other than m68k, mips, and arm64, everybody else that doesn't have
ARCH_NO_COHERENT_DMA_MMAP set uses this default implementation, so
I assume this behavior is acceptable on those architectures.
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 :)
Yeah, turns out it was just bad luck that I happened to run into these
crashes right after deciding to try out your patch :)
Reviewed-by: Alexey Kardashevskiy <a...@ozlabs.ru>
Thanks!
---
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 (sh...@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;
+}
