[PATCH v5 0/7] arm64: Default to 32-bit wide ZONE_DMA

[PATCH v5 0/7] arm64: Default to 32-bit wide ZONE_DMA

[Nicolas Saenz Julienne]

Using two distinct DMA zones turned out to be problematic. Here's an
attempt go back to a saner default.

I tested this on both a RPi4 and QEMU.

---

Changes since v4:
 - Fix of_dma_get_max_cpu_address() so it returns the last addressable
   addres, not the limit

Changes since v3:
 - Drop patch adding define in dma-mapping
 - Address small review changes
 - Update Ard's patch
 - Add new patch removing examples from mmzone.h

Changes since v2:
 - Introduce Ard's patch
 - Improve OF dma-ranges parsing function
 - Add unit test for OF function
 - Address small changes
 - Move crashkernel reservation later in boot process

Changes since v1:
 - Parse dma-ranges instead of using machine compatible string

Ard Biesheuvel (1):
  arm64: mm: Set ZONE_DMA size based on early IORT scan

Nicolas Saenz Julienne (6):
  arm64: mm: Move reserve_crashkernel() into mem_init()
  arm64: mm: Move zone_dma_bits initialization into zone_sizes_init()
  of/address: Introduce of_dma_get_max_cpu_address()
  of: unittest: Add test for of_dma_get_max_cpu_address()
  arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges
  mm: Remove examples from enum zone_type comment

 arch/arm64/mm/init.c      | 16 ++++++------
 drivers/acpi/arm64/iort.c | 52 +++++++++++++++++++++++++++++++++++++++
 drivers/of/address.c      | 42 +++++++++++++++++++++++++++++++
 drivers/of/unittest.c     | 18 ++++++++++++++
 include/linux/acpi_iort.h |  4 +++
 include/linux/mmzone.h    | 20 ---------------
 include/linux/of.h        |  7 ++++++
 7 files changed, 130 insertions(+), 29 deletions(-)

-- 
2.29.0

[PATCH v5 7/7] mm: Remove examples from enum zone_type comment

[Nicolas Saenz Julienne]

We can't really list every setup in common code. On top of that they are
unlikely to stay true for long as things change in the arch trees
independently of this comment.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/mmzone.h | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fb3bf696c05e..9d0c454d23cd 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -354,26 +354,6 @@ enum zone_type {
 	 * DMA mask is assumed when ZONE_DMA32 is defined. Some 64-bit
 	 * platforms may need both zones as they support peripherals with
 	 * different DMA addressing limitations.
-	 *
-	 * Some examples:
-	 *
-	 *  - i386 and x86_64 have a fixed 16M ZONE_DMA and ZONE_DMA32 for the
-	 *    rest of the lower 4G.
-	 *
-	 *  - arm only uses ZONE_DMA, the size, up to 4G, may vary depending on
-	 *    the specific device.
-	 *
-	 *  - arm64 has a fixed 1G ZONE_DMA and ZONE_DMA32 for the rest of the
-	 *    lower 4G.
-	 *
-	 *  - powerpc only uses ZONE_DMA, the size, up to 2G, may vary
-	 *    depending on the specific device.
-	 *
-	 *  - s390 uses ZONE_DMA fixed to the lower 2G.
-	 *
-	 *  - ia64 and riscv only use ZONE_DMA32.
-	 *
-	 *  - parisc uses neither.
 	 */
 #ifdef CONFIG_ZONE_DMA
 	ZONE_DMA,
-- 
2.29.0

Re: [PATCH v5 0/7] arm64: Default to 32-bit wide ZONE_DMA

[Catalin Marinas]

On Thu, Oct 29, 2020 at 06:25:43PM +0100, Nicolas Saenz Julienne wrote:
> Ard Biesheuvel (1):
>   arm64: mm: Set ZONE_DMA size based on early IORT scan
> 
> Nicolas Saenz Julienne (6):
>   arm64: mm: Move reserve_crashkernel() into mem_init()
>   arm64: mm: Move zone_dma_bits initialization into zone_sizes_init()
>   of/address: Introduce of_dma_get_max_cpu_address()
>   of: unittest: Add test for of_dma_get_max_cpu_address()
>   arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges
>   mm: Remove examples from enum zone_type comment

Thanks for putting this together. I had a minor comment but the patches
look fine to me. We still need an ack from Rob on the DT patch and I can
queue the series for 5.11.

Could you please also test the patch below on top of this series? It's
the removal of the implied DMA offset in the max_zone_phys()
calculation.

--------------------------8<-----------------------------
From 3ae252d888be4984a612236124f5b099e804c745 Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Fri, 30 Oct 2020 18:07:34 +0000
Subject: [PATCH] arm64: Ignore any DMA offsets in the max_zone_phys()
 calculation

Currently, the kernel assumes that if RAM starts above 32-bit (or
zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and
such constrained devices have a hardwired DMA offset. In practice, we
haven't noticed any such hardware so let's assume that we can expand
ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly,
ZONE_DMA is expanded to the 4GB limit if no RAM addressable by
zone_bits.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/mm/init.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 095540667f0f..362160e16fb2 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -175,14 +175,21 @@ static void __init reserve_elfcorehdr(void)
 #endif /* CONFIG_CRASH_DUMP */
 
 /*
- * Return the maximum physical address for a zone with a given address size
- * limit. It currently assumes that for memory starting above 4G, 32-bit
- * devices will use a DMA offset.
+ * Return the maximum physical address for a zone accessible by the given bits
+ * limit. If the DRAM starts above 32-bit, expand the zone to the maximum
+ * available memory, otherwise cap it at 32-bit.
  */
 static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
 {
-	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
-	return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
+	phys_addr_t zone_mask = (1ULL << zone_bits) - 1;
+	phys_addr_t phys_start = memblock_start_of_DRAM();
+
+	if (!(phys_start & U32_MAX))
+		zone_mask = PHYS_ADDR_MAX;
+	else if (!(phys_start & zone_mask))
+		zone_mask = U32_MAX;
+
+	return min(zone_mask + 1, memblock_end_of_DRAM());
 }
 
 static void __init zone_sizes_init(unsigned long min, unsigned long max)

Re: [PATCH v5 0/7] arm64: Default to 32-bit wide ZONE_DMA

[Nicolas Saenz Julienne]

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On Fri, 2020-10-30 at 18:11 +0000, Catalin Marinas wrote:
> On Thu, Oct 29, 2020 at 06:25:43PM +0100, Nicolas Saenz Julienne wrote:
> > Ard Biesheuvel (1):
> >   arm64: mm: Set ZONE_DMA size based on early IORT scan
> > 
> > Nicolas Saenz Julienne (6):
> >   arm64: mm: Move reserve_crashkernel() into mem_init()
> >   arm64: mm: Move zone_dma_bits initialization into zone_sizes_init()
> >   of/address: Introduce of_dma_get_max_cpu_address()
> >   of: unittest: Add test for of_dma_get_max_cpu_address()
> >   arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges
> >   mm: Remove examples from enum zone_type comment
> 
> Thanks for putting this together. I had a minor comment but the patches
> look fine to me. We still need an ack from Rob on the DT patch and I can
> queue the series for 5.11.

I'm preparing a v6 unifying both functions as you suggested.

> Could you please also test the patch below on top of this series? It's
> the removal of the implied DMA offset in the max_zone_phys()
> calculation.

Yes, happily. Comments below.

> --------------------------8<-----------------------------
> From 3ae252d888be4984a612236124f5b099e804c745 Mon Sep 17 00:00:00 2001
> From: Catalin Marinas <catalin.marinas@arm.com>
> Date: Fri, 30 Oct 2020 18:07:34 +0000
> Subject: [PATCH] arm64: Ignore any DMA offsets in the max_zone_phys()
>  calculation
> 
> Currently, the kernel assumes that if RAM starts above 32-bit (or
> zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and
> such constrained devices have a hardwired DMA offset. In practice, we
> haven't noticed any such hardware so let's assume that we can expand
> ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly,
> ZONE_DMA is expanded to the 4GB limit if no RAM addressable by
> zone_bits.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> ---
>  arch/arm64/mm/init.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 095540667f0f..362160e16fb2 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -175,14 +175,21 @@ static void __init reserve_elfcorehdr(void)
>  #endif /* CONFIG_CRASH_DUMP */
>  
>  /*
> - * Return the maximum physical address for a zone with a given address size
> - * limit. It currently assumes that for memory starting above 4G, 32-bit
> - * devices will use a DMA offset.
> + * Return the maximum physical address for a zone accessible by the given bits
> + * limit. If the DRAM starts above 32-bit, expand the zone to the maximum
> + * available memory, otherwise cap it at 32-bit.
>   */
>  static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
>  {
> -	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
> -	return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
> +	phys_addr_t zone_mask = (1ULL << zone_bits) - 1;

Maybe use DMA_BIT_MASK(), instead of the manual calculation?

> +	phys_addr_t phys_start = memblock_start_of_DRAM();
> +
> +	if (!(phys_start & U32_MAX))

I'd suggest using 'bigger than' instead of masks. Just to cover ourselves
against memory starting at odd locations. Also it'll behaves properly when
phys_start is zero (this breaks things on RPi4).

> +		zone_mask = PHYS_ADDR_MAX;
> +	else if (!(phys_start & zone_mask))
> +		zone_mask = U32_MAX;
> +
> +	return min(zone_mask + 1, memblock_end_of_DRAM());

This + 1 isn't going to play well when zone_mask is PHYS_ADDR_MAX.

Regards,
Nicolas


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Re: [PATCH v5 0/7] arm64: Default to 32-bit wide ZONE_DMA

[Catalin Marinas]

On Tue, Nov 03, 2020 at 06:00:33PM +0100, Nicolas Saenz Julienne wrote:
> On Fri, 2020-10-30 at 18:11 +0000, Catalin Marinas wrote:
> > On Thu, Oct 29, 2020 at 06:25:43PM +0100, Nicolas Saenz Julienne wrote:
> > > Ard Biesheuvel (1):
> > >   arm64: mm: Set ZONE_DMA size based on early IORT scan
> > > 
> > > Nicolas Saenz Julienne (6):
> > >   arm64: mm: Move reserve_crashkernel() into mem_init()
> > >   arm64: mm: Move zone_dma_bits initialization into zone_sizes_init()
> > >   of/address: Introduce of_dma_get_max_cpu_address()
> > >   of: unittest: Add test for of_dma_get_max_cpu_address()
> > >   arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges
> > >   mm: Remove examples from enum zone_type comment
> > 
> > Thanks for putting this together. I had a minor comment but the patches
> > look fine to me. We still need an ack from Rob on the DT patch and I can
> > queue the series for 5.11.
> 
> I'm preparing a v6 unifying both functions as you suggested.
> 
> > Could you please also test the patch below on top of this series? It's
> > the removal of the implied DMA offset in the max_zone_phys()
> > calculation.
> 
> Yes, happily. Comments below.
> 
> > --------------------------8<-----------------------------
> > From 3ae252d888be4984a612236124f5b099e804c745 Mon Sep 17 00:00:00 2001
> > From: Catalin Marinas <catalin.marinas@arm.com>
> > Date: Fri, 30 Oct 2020 18:07:34 +0000
> > Subject: [PATCH] arm64: Ignore any DMA offsets in the max_zone_phys()
> >  calculation
> > 
> > Currently, the kernel assumes that if RAM starts above 32-bit (or
> > zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and
> > such constrained devices have a hardwired DMA offset. In practice, we
> > haven't noticed any such hardware so let's assume that we can expand
> > ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly,
> > ZONE_DMA is expanded to the 4GB limit if no RAM addressable by
> > zone_bits.
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > ---
> >  arch/arm64/mm/init.c | 17 ++++++++++++-----
> >  1 file changed, 12 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 095540667f0f..362160e16fb2 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -175,14 +175,21 @@ static void __init reserve_elfcorehdr(void)
> >  #endif /* CONFIG_CRASH_DUMP */
> >  
> >  /*
> > - * Return the maximum physical address for a zone with a given address size
> > - * limit. It currently assumes that for memory starting above 4G, 32-bit
> > - * devices will use a DMA offset.
> > + * Return the maximum physical address for a zone accessible by the given bits
> > + * limit. If the DRAM starts above 32-bit, expand the zone to the maximum
> > + * available memory, otherwise cap it at 32-bit.
> >   */
> >  static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
> >  {
> > -	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
> > -	return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
> > +	phys_addr_t zone_mask = (1ULL << zone_bits) - 1;
> 
> Maybe use DMA_BIT_MASK(), instead of the manual calculation?

Yes.

> 
> > +	phys_addr_t phys_start = memblock_start_of_DRAM();
> > +
> > +	if (!(phys_start & U32_MAX))
> 
> I'd suggest using 'bigger than' instead of masks. Just to cover ourselves
> against memory starting at odd locations. Also it'll behaves properly when
> phys_start is zero (this breaks things on RPi4).

Good point.

> > +		zone_mask = PHYS_ADDR_MAX;
> > +	else if (!(phys_start & zone_mask))
> > +		zone_mask = U32_MAX;
> > +
> > +	return min(zone_mask + 1, memblock_end_of_DRAM());
> 
> This + 1 isn't going to play well when zone_mask is PHYS_ADDR_MAX.

You are right on PHYS_ADDR_MAX overflowing but I'd keep the +1 since
memblock_end_of_DRAM() returns the first byte past the accessible range
(so exclusive end).

I'll tweak this function a bit to avoid the overflow or use the
arm64-specific PHYS_MASK (that's never going to be the full 64 bits).

Thanks.

-- 
Catalin