Re: [PATCH] [PATCH] ARM64: Setup DMA32 zone size by bootargs

[Mike Rapoport <rppt@kernel.org>]

On Tue, Sep 15, 2020 at 11:08:55PM +0800, Phil Chang wrote:
> Allowing the DMA32 zone be configurable in ARM64 but at most 4Gb.

Please add more details why would you like to limit the DMA32 zone.

> Signed-off-by: Alix Wu <alix.wu@mediatek.com>
> Signed-off-by: YJ Chiang <yj.chiang@mediatek.com>
> Signed-off-by: Phil Chang <phil.chang@mediatek.com>
> ---
> 
>  .../admin-guide/kernel-parameters.txt         |  3 ++
>  arch/arm64/include/asm/memory.h               |  2 +
>  arch/arm64/mm/init.c                          | 39 +++++++++++++++++--
>  3 files changed, 41 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index bdc1f33fd3d1..5be6259e9ba8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -980,6 +980,9 @@
>  			The filter can be disabled or changed to another
>  			driver later using sysfs.
>  
> +	dma32_size=nn[MG]  [KNL,BOOT,ARM64]
> +			Forces the DMA32 zone size of <nn> in MB.

Most of the kernel parameters that deal with memory sizes allow either
of [KMG] suffixes.

> +
>  	driver_async_probe=  [KNL]
>  			List of driver names to be probed asynchronously.
>  			Format: <driver_name1>,<driver_name2>...
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index afa722504bfd..710de08ae8ae 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -175,6 +175,8 @@ extern u64			kimage_vaddr;
>  /* the offset between the kernel virtual and physical mappings */
>  extern u64			kimage_voffset;
>  
> +extern phys_addr_t		dma32_zone_size;
> +
>  static inline unsigned long kaslr_offset(void)
>  {
>  	return kimage_vaddr - KIMAGE_VADDR;
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 481d22c32a2e..c8af53680d46 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -60,6 +60,9 @@ EXPORT_SYMBOL(physvirt_offset);
>  struct page *vmemmap __ro_after_init;
>  EXPORT_SYMBOL(vmemmap);
>  
> +phys_addr_t dma32_zone_size __ro_after_init;
> +EXPORT_SYMBOL(dma32_zone_size);
> +
>  /*
>   * 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
> @@ -242,6 +245,29 @@ static int __init early_mem(char *p)
>  }
>  early_param("mem", early_mem);
>  
> +static int __init setup_dma32_zone(char *p)
> +{
> +	u64 size;
> +
> +	if (!p)
> +		return -EINVAL;
> +
> +	if (kstrtoull(p, 0, &size))
> +		return -EINVAL;

Better to use memparse() here.

> +
> +	/* DMA32 zone size should never grater than 4G */
> +	if (size > max_zone_phys(32) / SZ_1M)
> +		return -EINVAL;
> +
> +	pr_notice("Setup dma32 zone size to %llu Mb\n", size);
> +
> +	dma32_zone_size = size * SZ_1M;
> +
> +	return 0;
> +}
> +
> +early_param("dma32_size", setup_dma32_zone);
> +
>  static int __init early_init_dt_scan_usablemem(unsigned long node,
>  		const char *uname, int depth, void *data)
>  {
> @@ -392,10 +418,17 @@ void __init arm64_memblock_init(void)
>  		arm64_dma_phys_limit = max_zone_phys(ARM64_ZONE_DMA_BITS);
>  	}
>  
> -	if (IS_ENABLED(CONFIG_ZONE_DMA32))
> -		arm64_dma32_phys_limit = max_zone_phys(32);
> -	else
> +	if (IS_ENABLED(CONFIG_ZONE_DMA32)) {
> +		if (dma32_zone_size) {
> +			arm64_dma32_phys_limit = min(max_zone_phys(32),
> +				dma32_zone_size + memblock_start_of_DRAM());
> +		} else {
> +			arm64_dma32_phys_limit = max_zone_phys(32);
> +			dma32_zone_size = arm64_dma32_phys_limit;
> +		}

I think this calculations can be hidden in max_zone_phys(), e.g.

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 481d22c32a2e..be3fdfb35a56 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -189,7 +189,12 @@ static void __init reserve_elfcorehdr(void)
 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_size = (1ULL << zone_bits);
+
+	if (IS_ENABLED(CONFIG_ZONE_DMA32) && zone_bits == 32 && dma32_zone_size)
+		zone_bits = min(zone_size,dma32_zone_size);
+
+	return min(offset + zone_size, memblock_end_of_DRAM());
 }
 
 static void __init zone_sizes_init(unsigned long min, unsigned long max)

> +	} else {
>  		arm64_dma32_phys_limit = PHYS_MASK + 1;
> +	}
>  
>  	reserve_crashkernel();
>  
> -- 
> 2.18.0

-- 
Sincerely yours,
Mike.