Re: [PATCH v6 3/4] arm64: use both ZONE_DMA and ZONE_DMA32

[Qian Cai]

> On Sep 11, 2019, at 2:25 PM, Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx> wrote:
> 
> So far all arm64 devices have supported 32 bit DMA masks for their
> peripherals. This is not true anymore for the Raspberry Pi 4 as most of
> it's peripherals can only address the first GB of memory on a total of
> up to 4 GB.
> 
> This goes against ZONE_DMA32's intent, as it's expected for ZONE_DMA32
> to be addressable with a 32 bit mask. So it was decided to re-introduce
> ZONE_DMA in arm64.
> 
> ZONE_DMA will contain the lower 1G of memory, which is currently the
> memory area addressable by any peripheral on an arm64 device.
> ZONE_DMA32 will contain the rest of the 32 bit addressable memory.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> 
> ---
> 
> I kept the Reviewed-by as the last bug solution was proposed by Catalin
> 
> Changes in v6:
> - Fixed bug in max_zone_phys
> 
> Changes in v5:
> - Fixed swiotlb initialization
> 
> Changes in v4:
> - Fixed issue when NUMA=n and ZONE_DMA=n
> - Merged two max_zone_dma*_phys() functions
> 
> Changes in v3:
> - Used fixed size ZONE_DMA
> - Fix check befor swiotlb_init()
> 
> Changes in v2:
> - Update comment to reflect new zones split
> - ZONE_DMA will never be left empty
> 
> arch/arm64/Kconfig            |  4 +++
> arch/arm64/include/asm/page.h |  2 ++
> arch/arm64/mm/init.c          | 54 +++++++++++++++++++++++++----------
> 3 files changed, 45 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6b6362b83004..2dbe0165bd15 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -267,6 +267,10 @@ config GENERIC_CSUM
> config GENERIC_CALIBRATE_DELAY
> 	def_bool y
> 
> +config ZONE_DMA
> +	bool "Support DMA zone" if EXPERT
> +	default y
> +
> config ZONE_DMA32
> 	bool "Support DMA32 zone" if EXPERT
> 	default y
> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
> index d39ddb258a04..7b8c98830101 100644
> --- a/arch/arm64/include/asm/page.h
> +++ b/arch/arm64/include/asm/page.h
> @@ -38,4 +38,6 @@ extern int pfn_valid(unsigned long);
> 
> #include <asm-generic/getorder.h>
> 
> +#define ARCH_ZONE_DMA_BITS 30
> +
> #endif
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 8e9bc64c5878..44f07fdf7a59 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -56,6 +56,13 @@ EXPORT_SYMBOL(physvirt_offset);
> struct page *vmemmap __ro_after_init;
> EXPORT_SYMBOL(vmemmap);
> 
> +/*
> + * We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA covers the first 1G of
> + * memory as some devices, namely the Raspberry Pi 4, have peripherals with
> + * this limited view of the memory. ZONE_DMA32 will cover the rest of the 32
> + * bit addressable memory area.
> + */
> +phys_addr_t arm64_dma_phys_limit __ro_after_init;
> phys_addr_t arm64_dma32_phys_limit __ro_after_init;
> 
> #ifdef CONFIG_KEXEC_CORE
> @@ -169,15 +176,16 @@ static void __init reserve_elfcorehdr(void)
> {
> }
> #endif /* CONFIG_CRASH_DUMP */
> +
> /*
> - * Return the maximum physical address for ZONE_DMA32 (DMA_BIT_MASK(32)). 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 with a given address size
> + * limit. It currently assumes that for memory starting above 4G, 32-bit
> + * devices will use a DMA offset.
>  */
> -static phys_addr_t __init max_zone_dma32_phys(void)
> +static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
> {
> -	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, 32);
> -	return min(offset + (1ULL << 32), memblock_end_of_DRAM());
> +	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
> +	return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
> }
> 
> #ifdef CONFIG_NUMA
> @@ -186,6 +194,9 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
> {
> 	unsigned long max_zone_pfns[MAX_NR_ZONES]  = {0};
> 
> +#ifdef CONFIG_ZONE_DMA
> +	max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
> +#endif
> #ifdef CONFIG_ZONE_DMA32
> 	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(arm64_dma32_phys_limit);
> #endif
> @@ -201,13 +212,18 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
> 	struct memblock_region *reg;
> 	unsigned long zone_size[MAX_NR_ZONES], zhole_size[MAX_NR_ZONES];
> 	unsigned long max_dma32 = min;
> +	unsigned long max_dma = min;
> 
> 	memset(zone_size, 0, sizeof(zone_size));
> 
> -	/* 4GB maximum for 32-bit only capable devices */
> +#ifdef CONFIG_ZONE_DMA
> +	max_dma = PFN_DOWN(arm64_dma_phys_limit);
> +	zone_size[ZONE_DMA] = max_dma - min;
> +	max_dma32 = max_dma;
> +#endif
> #ifdef CONFIG_ZONE_DMA32
> 	max_dma32 = PFN_DOWN(arm64_dma32_phys_limit);
> -	zone_size[ZONE_DMA32] = max_dma32 - min;
> +	zone_size[ZONE_DMA32] = max_dma32 - max_dma;
> #endif
> 	zone_size[ZONE_NORMAL] = max - max_dma32;
> 
> @@ -219,11 +235,17 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
> 
> 		if (start >= max)
> 			continue;
> -
> +#ifdef CONFIG_ZONE_DMA
> +		if (start < max_dma) {
> +			unsigned long dma_end = min_not_zero(end, max_dma);
> +			zhole_size[ZONE_DMA] -= dma_end - start;
> +		}
> +#endif
> #ifdef CONFIG_ZONE_DMA32
> 		if (start < max_dma32) {
> -			unsigned long dma_end = min(end, max_dma32);
> -			zhole_size[ZONE_DMA32] -= dma_end - start;
> +			unsigned long dma32_end = min(end, max_dma32);
> +			unsigned long dma32_start = max(start, max_dma);
> +			zhole_size[ZONE_DMA32] -= dma32_end - dma32_start;
> 		}
> #endif
> 		if (end > max_dma32) {
> @@ -418,9 +440,11 @@ void __init arm64_memblock_init(void)
> 
> 	early_init_fdt_scan_reserved_mem();
> 
> -	/* 4GB maximum for 32-bit only capable devices */
> +	if (IS_ENABLED(CONFIG_ZONE_DMA))
> +		arm64_dma_phys_limit = max_zone_phys(ARCH_ZONE_DMA_BITS);
> +
> 	if (IS_ENABLED(CONFIG_ZONE_DMA32))
> -		arm64_dma32_phys_limit = max_zone_dma32_phys();
> +		arm64_dma32_phys_limit = max_zone_phys(32);
> 	else
> 		arm64_dma32_phys_limit = PHYS_MASK + 1;
> 
> @@ -430,7 +454,7 @@ void __init arm64_memblock_init(void)
> 
> 	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
> 
> -	dma_contiguous_reserve(arm64_dma32_phys_limit);
> +	dma_contiguous_reserve(arm64_dma_phys_limit ? : arm64_dma32_phys_limit);
> }
> 
> void __init bootmem_init(void)
> @@ -534,7 +558,7 @@ static void __init free_unused_memmap(void)
> void __init mem_init(void)
> {
> 	if (swiotlb_force == SWIOTLB_FORCE ||
> -	    max_pfn > (arm64_dma32_phys_limit >> PAGE_SHIFT))
> +	    max_pfn > PFN_DOWN(arm64_dma_phys_limit ? : arm64_dma32_phys_limit))
> 		swiotlb_init(1);
> 	else
> 		swiotlb_force = SWIOTLB_NO_FORCE;
> -- 
> 2.23.0
> 
> 

With ZONE_DMA=y, this config will fail to reserve 512M CMA on a server,

https://raw.githubusercontent.com/cailca/linux-mm/master/arm64.config

CONFIG_DMA_CMA=y
CONFIG_CMA_SIZE_MBYTES=64
CONFIG_CMA_SIZE_SEL_MBYTES=y
CONFIG_CMA_ALIGNMENT=8
CONFIG_CMA=y
CONFIG_CMA_DEBUGFS=y
CONFIG_CMA_AREAS=7

Is this expected?