fix default dma_mmap_* pgprot v2

fix default dma_mmap_* pgprot v2

[Christoph Hellwig]

Hi all,

As Shawn pointed out we've had issues with the dma mmap pgprots ever
since the dma_common_mmap helper was added beyong the initial
architectures - we default to uncached mappings, but for devices that
are DMA coherent, or if the DMA_ATTR_NON_CONSISTENT is set (and
supported) this can lead to aliasing of cache attributes.  This patch
fixes that.  My explanation of why this hasn't been much of an issue
is that the dma_mmap_ helpers aren't used widely and mostly just in
architecture specific drivers.

Changes since v1:
 - fix handling of DMA_ATTR_NON_CONSISTENT where it is a no-op
   (which is most architectures)
 - remove DMA_ATTR_WRITE_COMBINE on mips, as it seem dangerous as-is

[PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Christoph Hellwig]

All the way back to introducing dma_common_mmap we've defaulyed to mark
the pages as uncached.  But this is wrong for DMA coherent devices.
Later on DMA_ATTR_WRITE_COMBINE also got incorrect treatment as that
flag is only treated special on the alloc side for non-coherent devices.

Introduce a new dma_pgprot helper that deals with the check for coherent
devices so that only the remapping cases even reach arch_dma_mmap_pgprot
and we thus ensure no aliasing of page attributes happens, which makes
the powerpc version of arch_dma_mmap_pgprot obsolete and simplifies the
remaining ones.

Note that this means arch_dma_mmap_pgprot is a bit misnamed now, but
we'll phase it out soon.

Fixes: 64ccc9c033c6 ("common: dma-mapping: add support for generic dma_mmap_* calls")
Reported-by: Shawn Anastasio <shawn@anastas.io>
Reported-by: Gavin Li <git@thegavinli.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/arm/mm/dma-mapping.c        |  4 +---
 arch/arm64/mm/dma-mapping.c      |  4 +---
 arch/powerpc/Kconfig             |  1 -
 arch/powerpc/kernel/dma-common.c | 17 -----------------
 drivers/iommu/dma-iommu.c        |  6 +++---
 include/linux/dma-mapping.h      |  1 +
 include/linux/dma-noncoherent.h  |  5 -----
 kernel/dma/mapping.c             | 17 ++++++++++++++++-
 kernel/dma/remap.c               |  2 +-
 9 files changed, 23 insertions(+), 34 deletions(-)
 delete mode 100644 arch/powerpc/kernel/dma-common.c

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 6774b03aa405..d42557ee69c2 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -2405,9 +2405,7 @@ long arch_dma_coherent_to_pfn(struct device *dev, void *cpu_addr,
 pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
 		unsigned long attrs)
 {
-	if (!dev_is_dma_coherent(dev))
-		return __get_dma_pgprot(attrs, prot);
-	return prot;
+	return __get_dma_pgprot(attrs, prot);
 }
 
 void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 1d3f0b5a9940..bd2b039f43a6 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -14,9 +14,7 @@
 pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
 		unsigned long attrs)
 {
-	if (!dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_WRITE_COMBINE))
-		return pgprot_writecombine(prot);
-	return prot;
+	return pgprot_writecombine(prot);
 }
 
 void arch_sync_dma_for_device(struct device *dev, phys_addr_t paddr,
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 77f6ebf97113..d8dcd8820369 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -121,7 +121,6 @@ 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/dma-common.c b/arch/powerpc/kernel/dma-common.c
deleted file mode 100644
index dc7ef6b17b69..000000000000
--- a/arch/powerpc/kernel/dma-common.c
+++ /dev/null
@@ -1,17 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * Contains common dma routines for all powerpc platforms.
- *
- * Copyright (C) 2019 Shawn Anastasio.
- */
-
-#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;
-}
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index a7f9c3edbcb2..0015fe610b23 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -574,7 +574,7 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
 	struct iova_domain *iovad = &cookie->iovad;
 	bool coherent = dev_is_dma_coherent(dev);
 	int ioprot = dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs);
-	pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
+	pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
 	unsigned int count, min_size, alloc_sizes = domain->pgsize_bitmap;
 	struct page **pages;
 	struct sg_table sgt;
@@ -975,7 +975,7 @@ static void *iommu_dma_alloc_pages(struct device *dev, size_t size,
 		return NULL;
 
 	if (IS_ENABLED(CONFIG_DMA_REMAP) && (!coherent || PageHighMem(page))) {
-		pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
+		pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);
 
 		cpu_addr = dma_common_contiguous_remap(page, alloc_size,
 				VM_USERMAP, prot, __builtin_return_address(0));
@@ -1035,7 +1035,7 @@ static int iommu_dma_mmap(struct device *dev, struct vm_area_struct *vma,
 	unsigned long pfn, off = vma->vm_pgoff;
 	int ret;
 
-	vma->vm_page_prot = arch_dma_mmap_pgprot(dev, vma->vm_page_prot, attrs);
+	vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
 
 	if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
 		return ret;
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index f7d1eea32c78..3dda399ec9ce 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -611,6 +611,7 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
 #define dma_get_sgtable(d, t, v, h, s) dma_get_sgtable_attrs(d, t, v, h, s, 0)
 #define dma_mmap_coherent(d, v, c, h, s) dma_mmap_attrs(d, v, c, h, s, 0)
 
+pgprot_t dma_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs);
 extern int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
 		void *cpu_addr, dma_addr_t dma_addr, size_t size,
 		unsigned long attrs);
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index 3813211a9aad..9ae5cee543c4 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -42,13 +42,8 @@ void arch_dma_free(struct device *dev, size_t size, void *cpu_addr,
 		dma_addr_t dma_addr, unsigned long attrs);
 long arch_dma_coherent_to_pfn(struct device *dev, void *cpu_addr,
 		dma_addr_t dma_addr);
-
-#ifdef CONFIG_ARCH_HAS_DMA_MMAP_PGPROT
 pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
 		unsigned long attrs);
-#else
-# define arch_dma_mmap_pgprot(dev, prot, attrs)	pgprot_noncached(prot)
-#endif
 
 #ifdef CONFIG_DMA_NONCOHERENT_CACHE_SYNC
 void arch_dma_cache_sync(struct device *dev, void *vaddr, size_t size,
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index b945239621d8..51d9657e0a8f 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -150,6 +150,21 @@ int dma_get_sgtable_attrs(struct device *dev, struct sg_table *sgt,
 }
 EXPORT_SYMBOL(dma_get_sgtable_attrs);
 
+/*
+ * Return the page attributes used for mapping dma_alloc_* memory, either in
+ * kernel space if remapping is needed, or to userspace through dma_mmap_*.
+ */
+pgprot_t dma_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs)
+{
+	if (dev_is_dma_coherent(dev) ||
+	    (IS_ENABLED(CONFIG_DMA_NONCOHERENT_CACHE_SYNC) &&
+             (attrs & DMA_ATTR_NON_CONSISTENT)))
+		return prot;
+	if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_MMAP_PGPROT))
+		return arch_dma_mmap_pgprot(dev, prot, attrs);
+	return pgprot_noncached(prot);
+}
+
 /*
  * Create userspace mapping for the DMA-coherent memory.
  */
@@ -164,7 +179,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
 	unsigned long pfn;
 	int ret = -ENXIO;
 
-	vma->vm_page_prot = arch_dma_mmap_pgprot(dev, vma->vm_page_prot, attrs);
+	vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
 
 	if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
 		return ret;
diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c
index a594aec07882..ffe78f0b2fe4 100644
--- a/kernel/dma/remap.c
+++ b/kernel/dma/remap.c
@@ -218,7 +218,7 @@ void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
 
 	/* create a coherent mapping */
 	ret = dma_common_contiguous_remap(page, size, VM_USERMAP,
-			arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs),
+			dma_pgprot(dev, PAGE_KERNEL, attrs),
 			__builtin_return_address(0));
 	if (!ret) {
 		__dma_direct_free_pages(dev, size, page);
-- 
2.20.1

[PATCH 2/2] MIPS: remove support for DMA_ATTR_WRITE_COMBINE

[Christoph Hellwig]

Mips uses the KSEG1 kernel memory segment do map dma coherent
allocations for non-coherent devices as uncachable, and does not have
any kind of special support for DMA_ATTR_WRITE_COMBINE in the allocation
path.  Thus supporting DMA_ATTR_WRITE_COMBINE in dma_mmap_attrs will
lead to multiple mappings with different caching attributes.

Fixes: 8c172467be36 ("MIPS: Add implementation of dma_map_ops.mmap()")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/mips/Kconfig              | 1 -
 arch/mips/mm/dma-noncoherent.c | 8 --------
 2 files changed, 9 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index d50fafd7bf3a..86e6760ef0d0 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1119,7 +1119,6 @@ config DMA_PERDEV_COHERENT
 
 config DMA_NONCOHERENT
 	bool
-	select ARCH_HAS_DMA_MMAP_PGPROT
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select ARCH_HAS_UNCACHED_SEGMENT
 	select NEED_DMA_MAP_STATE
diff --git a/arch/mips/mm/dma-noncoherent.c b/arch/mips/mm/dma-noncoherent.c
index ed56c6fa7be2..1d4d57dd9acf 100644
--- a/arch/mips/mm/dma-noncoherent.c
+++ b/arch/mips/mm/dma-noncoherent.c
@@ -65,14 +65,6 @@ long arch_dma_coherent_to_pfn(struct device *dev, void *cpu_addr,
 	return page_to_pfn(virt_to_page(cached_kernel_address(cpu_addr)));
 }
 
-pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
-		unsigned long attrs)
-{
-	if (attrs & DMA_ATTR_WRITE_COMBINE)
-		return pgprot_writecombine(prot);
-	return pgprot_noncached(prot);
-}
-
 static inline void dma_sync_virt(void *addr, size_t size,
 		enum dma_data_direction dir)
 {
-- 
2.20.1

Re: [PATCH 2/2] MIPS: remove support for DMA_ATTR_WRITE_COMBINE

[Sergei Shtylyov]

Hello!

On 05.08.2019 11:01, Christoph Hellwig wrote:

> Mips uses the KSEG1 kernel memory segment do map dma coherent

     MIPS. s/do/to/?

> allocations for n

on-coherent devices as uncachable, and does not have

    Uncacheable?

> any kind of special support for DMA_ATTR_WRITE_COMBINE in the allocation
> path.  Thus supporting DMA_ATTR_WRITE_COMBINE in dma_mmap_attrs will
> lead to multiple mappings with different caching attributes.
> 
> Fixes: 8c172467be36 ("MIPS: Add implementation of dma_map_ops.mmap()")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
[...]

MBR, Sergei

Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Catalin Marinas]

On Mon, Aug 05, 2019 at 11:01:44AM +0300, Christoph Hellwig wrote:
> All the way back to introducing dma_common_mmap we've defaulyed to mark

s/defaultyed/defaulted/

> the pages as uncached.  But this is wrong for DMA coherent devices.
> Later on DMA_ATTR_WRITE_COMBINE also got incorrect treatment as that
> flag is only treated special on the alloc side for non-coherent devices.
> 
> Introduce a new dma_pgprot helper that deals with the check for coherent
> devices so that only the remapping cases even reach arch_dma_mmap_pgprot

s/even/ever/

> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 1d3f0b5a9940..bd2b039f43a6 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -14,9 +14,7 @@
>  pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
>  		unsigned long attrs)
>  {
> -	if (!dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_WRITE_COMBINE))
> -		return pgprot_writecombine(prot);
> -	return prot;
> +	return pgprot_writecombine(prot);
>  }

For arm64:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Gavin Li]

>         /* create a coherent mapping */
>         ret = dma_common_contiguous_remap(page, size, VM_USERMAP,
> -                       arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs),
> +                       dma_pgprot(dev, PAGE_KERNEL, attrs),
>                         __builtin_return_address(0));
>         if (!ret) {
>                 __dma_direct_free_pages(dev, size, page);

Is dma_common_contiguous_remap() still necessary in the
DMA_ATTR_NON_CONSISTENT case? I would presume it would be fine to just
return a linearly mapped address in that case.

Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Christoph Hellwig]

On Mon, Aug 05, 2019 at 07:55:44PM -0700, Gavin Li wrote:
> >         /* create a coherent mapping */
> >         ret = dma_common_contiguous_remap(page, size, VM_USERMAP,
> > -                       arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs),
> > +                       dma_pgprot(dev, PAGE_KERNEL, attrs),
> >                         __builtin_return_address(0));
> >         if (!ret) {
> >                 __dma_direct_free_pages(dev, size, page);
> 
> Is dma_common_contiguous_remap() still necessary in the
> DMA_ATTR_NON_CONSISTENT case? I would presume it would be fine to just
> return a linearly mapped address in that case.

It would not be required for a real DMA_ATTR_NON_CONSISTENT
implementation.  But only parisc and mips actually properly implement
DMA_ATTR_NON_CONSISTENT, everyone ignores it.  Given that the API is
a little ill defined and I have a better replacement in the pipeline
I don't want to start implementing it for other architectures now.

Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Shawn Anastasio]

On 8/5/19 10:01 AM, Christoph Hellwig wrote:
> diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
> index 3813211a9aad..9ae5cee543c4 100644
> --- a/include/linux/dma-noncoherent.h
> +++ b/include/linux/dma-noncoherent.h
> @@ -42,13 +42,8 @@ void arch_dma_free(struct device *dev, size_t size, void *cpu_addr,
>   		dma_addr_t dma_addr, unsigned long attrs);
>   long arch_dma_coherent_to_pfn(struct device *dev, void *cpu_addr,
>   		dma_addr_t dma_addr);
> -
> -#ifdef CONFIG_ARCH_HAS_DMA_MMAP_PGPROT
>   pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
>   		unsigned long attrs);
> -#else
> -# define arch_dma_mmap_pgprot(dev, prot, attrs)	pgprot_noncached(prot)
> -#endif

Nit, but maybe the prototype should still be ifdef'd here? It at least
could prevent a reader from incorrectly thinking that the function is
always present.

Also, like Will mentioned earlier, the function name isn't entirely
accurate anymore. I second the suggestion of using something like
arch_dma_noncoherent_pgprot(). As for your idea of defining
pgprot_dmacoherent for all architectures as

#ifndef pgprot_dmacoherent
#define pgprot_dmacoherent pgprot_noncached
#endif

I think that the name here is kind of misleading too, since this
definition will only be used when there is no support for proper
DMA coherency.

Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Christoph Hellwig]

On Tue, Aug 06, 2019 at 09:39:06PM +0200, Shawn Anastasio wrote:
>> -#ifdef CONFIG_ARCH_HAS_DMA_MMAP_PGPROT
>>   pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
>>   		unsigned long attrs);
>> -#else
>> -# define arch_dma_mmap_pgprot(dev, prot, attrs)	pgprot_noncached(prot)
>> -#endif
>
> Nit, but maybe the prototype should still be ifdef'd here? It at least
> could prevent a reader from incorrectly thinking that the function is
> always present.

Actually it is typical modern Linux style to just provide a prototype
and then use "if (IS_ENABLED(CONFIG_FOO))" to guard the call(s) to it.

>
> Also, like Will mentioned earlier, the function name isn't entirely
> accurate anymore. I second the suggestion of using something like
> arch_dma_noncoherent_pgprot().

As mentioned I plan to remove arch_dma_mmap_pgprot for 5.4, so I'd
rather avoid churn for the short period of time.

> As for your idea of defining
> pgprot_dmacoherent for all architectures as
>
> #ifndef pgprot_dmacoherent
> #define pgprot_dmacoherent pgprot_noncached
> #endif
>
> I think that the name here is kind of misleading too, since this
> definition will only be used when there is no support for proper
> DMA coherency.

Do you have a suggestion for a better name?  I'm pretty bad at naming,
so just reusing the arm name seemed like a good way to avoid having
to make naming decisions myself.

Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Shawn Anastasio]

On 8/7/19 8:04 AM, Christoph Hellwig wrote:
> Actually it is typical modern Linux style to just provide a prototype
> and then use "if (IS_ENABLED(CONFIG_FOO))" to guard the call(s) to it.

I see.

>> Also, like Will mentioned earlier, the function name isn't entirely
>> accurate anymore. I second the suggestion of using something like
>> arch_dma_noncoherent_pgprot().
> 
> As mentioned I plan to remove arch_dma_mmap_pgprot for 5.4, so I'd
> rather avoid churn for the short period of time.

Yeah, fair enough.

>> As for your idea of defining
>> pgprot_dmacoherent for all architectures as
>>
>> #ifndef pgprot_dmacoherent
>> #define pgprot_dmacoherent pgprot_noncached
>> #endif
>>
>> I think that the name here is kind of misleading too, since this
>> definition will only be used when there is no support for proper
>> DMA coherency.
> 
> Do you have a suggestion for a better name?  I'm pretty bad at naming,
> so just reusing the arm name seemed like a good way to avoid having
> to make naming decisions myself.

Good question. Perhaps something like `pgprot_dmacoherent_fallback`
would better convey that this is only used for devices that don't
support DMA coherency? Or maybe `pgprot_dma_noncoherent`?