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Message-ID: <bff5ccf2-d748-6e72-79b7-9d211a9ad21e@huawei.com>
Date: Wed, 30 Mar 2022 17:24:56 +0800
From: Kefeng Wang <wangkefeng.wang@...wei.com>
To: Vijay Balakrishna <vijayb@...ux.microsoft.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>
CC: Pasha Tatashin <pasha.tatashin@...een.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH 1/2] arm64: mm: Do not defer reserve_crashkernel() if only
ZONE_DMA32
On 2022/3/30 6:29, Vijay Balakrishna wrote:
>
>
> On 3/24/2022 10:53 PM, Kefeng Wang wrote:
>> The kernel could be benifit due to BLOCK_MAPPINGS, see commit
>> 031495635b46 ("arm64: Do not defer reserve_crashkernel() for
>> platforms with no DMA memory zones"), if there is only with
>> ZONE_DMA32, we could set arm64_dma_phys_limit to max_zone_phys(32)
>> earlier in arm64_memblock_init(), then we will benifit too.
>
> Thanks for noticing platforms with just ZONE_DMA32 config can also
> benefit BLOCK_MAPPINGS. I assume you have access to one where you
> notice the difference with proposed changes and able to test. I did
> test proposed changes on SoC we use with IOMMU (no ZONE_DMA configs
> enabled).
>
> Nits --
> - benifit -> benefit
> - consider making commit message clear, "then we will.." seems you are
> referring to platforms with just ZONE_DMA32 config enabled
> - to reflect new change consider updating comment added in commit
> 031495635b46
>
One more question, could we add new cmdline(eg, dma_force_32bit) to let
the arm64 using
32bit dma by default? I think most platforms are not with small DMA
bit(only found 20bit in Raspberry Pi 4?),
Here is a draft(based on this patch) to do it, if the kernel boot with
this cmdline and even ZONE_DMA
is enabled, the kernel allows linear creation of block mapping, not sure
this is the right way, any suggestion? Thanks.
diff --git a/arch/arm64/include/asm/processor.h
b/arch/arm64/include/asm/processor.h
index 73e38d9a540c..8febed26aeed 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -100,6 +100,7 @@
base)
#endif /* CONFIG_ARM64_FORCE_52BIT */
+extern bool arm64_dma_force_32bit;
extern phys_addr_t arm64_dma_phys_limit;
#define ARCH_LOW_ADDRESS_LIMIT (arm64_dma_phys_limit - 1)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index d6f64819ef89..86aab5db735b 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -92,6 +92,16 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit;
phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
#endif
+bool __ro_after_init arm64_dma_force_32bit;
+static int __init arm64_dma_force_32bit_setup(char *p)
+{
+ arm64_dma_force_32bit = true;
+ zone_dma_bits = 32;
+
+ return 0;
+}
+early_param("dma_force_32bit", arm64_dma_force_32bit_setup);
+
/*
* reserve_crashkernel() - reserves memory for crash kernel
*
@@ -165,10 +175,11 @@ static void __init zone_sizes_init(void)
#ifdef CONFIG_ZONE_DMA
unsigned int acpi_zone_dma_bits;
unsigned int dt_zone_dma_bits;
-
- acpi_zone_dma_bits = fls64(acpi_iort_dma_get_max_cpu_address());
- dt_zone_dma_bits = fls64(of_dma_get_max_cpu_address(NULL));
- zone_dma_bits = min3(32U, dt_zone_dma_bits, acpi_zone_dma_bits);
+ if (!arm64_dma_force_32bit) {
+ acpi_zone_dma_bits =
fls64(acpi_iort_dma_get_max_cpu_address());
+ dt_zone_dma_bits = fls64(of_dma_get_max_cpu_address(NULL));
+ zone_dma_bits = min3(32U, dt_zone_dma_bits,
acpi_zone_dma_bits);
+ }
arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
#endif
@@ -336,7 +347,7 @@ void __init arm64_memblock_init(void)
early_init_fdt_scan_reserved_mem();
dma32_phys_limit = max_zone_phys(32);
- if (!IS_ENABLED(CONFIG_ZONE_DMA)) {
+ if (!IS_ENABLED(CONFIG_ZONE_DMA) || arm64_dma_force_32bit) {
if (IS_ENABLED(CONFIG_ZONE_DMA32))
arm64_dma_phys_limit = dma32_phys_limit;
reserve_crashkernel();
@@ -388,7 +399,7 @@ void __init bootmem_init(void)
* request_standard_resources() depends on crashkernel's memory
being
* reserved, so do it here.
*/
- if (IS_ENABLED(CONFIG_ZONE_DMA))
+ if (IS_ENABLED(CONFIG_ZONE_DMA) && !arm64_dma_force_32bit)
reserve_crashkernel();
memblock_dump_all();
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 23734481318a..9431ad581927 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -529,7 +529,7 @@ static void __init map_mem(pgd_t *pgdp)
#ifdef CONFIG_KEXEC_CORE
if (crash_mem_map) {
- if (IS_ENABLED(CONFIG_ZONE_DMA))
+ if (IS_ENABLED(CONFIG_ZONE_DMA) && !arm64_dma_force_32bit)
flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
else if (crashk_res.end)
memblock_mark_nomap(crashk_res.start,
@@ -570,7 +570,7 @@ static void __init map_mem(pgd_t *pgdp)
* through /sys/kernel/kexec_crash_size interface.
*/
#ifdef CONFIG_KEXEC_CORE
- if (crash_mem_map && !IS_ENABLED(CONFIG_ZONE_DMA)) {
+ if (crash_mem_map && (!IS_ENABLED(CONFIG_ZONE_DMA) ||
arm64_dma_force_32bit)) {
if (crashk_res.end) {
__map_memblock(pgdp, crashk_res.start,
crashk_res.end + 1,
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