commit 031495635b4668f94e964e037ca93d0d38bfde58 upstream.

The following patches resulted in deferring crash kernel reservation to mem_init(), mainly aimed at platforms with DMA memory zones (no IOMMU), in particular Raspberry Pi 4.

commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32") commit 8424ecdde7df ("arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges") commit 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into mem_init()") commit 2687275a5843 ("arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required")

Above changes introduced boot slowdown due to linear map creation for all the memory banks with NO_BLOCK_MAPPINGS, see discussion[1]. The proposed changes restore crash kernel reservation to earlier behavior thus avoids slow boot, particularly for platforms with IOMMU (no DMA memory zones).

Tested changes to confirm no ~150ms boot slowdown on our SoC with IOMMU and 8GB memory. Also tested with ZONE_DMA and/or ZONE_DMA32 configs to confirm no regression to deferring scheme of crash kernel memory reservation. In both cases successfully collected kernel crash dump.

[1] https://lore.kernel.org/all/9436d033-579b-55fa-9b00-6f4b661c2dd7@linux.micro...

Signed-off-by: Vijay Balakrishna vijayb@linux.microsoft.com Cc: stable@vger.kernel.org Reviewed-by: Pasha Tatashin pasha.tatashin@soleen.com Link: https://lore.kernel.org/r/1646242689-20744-1-git-send-email-vijayb@linux.mic... [will: Add #ifdef CONFIG_KEXEC_CORE guards to fix 'crashk_res' references in allnoconfig build] Signed-off-by: Will Deacon will@kernel.org --- arch/arm64/mm/init.c | 36 ++++++++++++++++++++++++++++++++---- arch/arm64/mm/mmu.c | 32 +++++++++++++++++++++++++++++++- 2 files changed, 63 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index c0a7f0d90b39..80cc79760e8e 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -58,8 +58,34 @@ EXPORT_SYMBOL(memstart_addr); * unless restricted on specific platforms (e.g. 30-bit on Raspberry Pi 4). * In such case, ZONE_DMA32 covers the rest of the 32-bit addressable memory, * otherwise it is empty. + * + * Memory reservation for crash kernel either done early or deferred + * depending on DMA memory zones configs (ZONE_DMA) -- + * + * In absence of ZONE_DMA configs arm64_dma_phys_limit initialized + * here instead of max_zone_phys(). This lets early reservation of + * crash kernel memory which has a dependency on arm64_dma_phys_limit. + * Reserving memory early for crash kernel allows linear creation of block + * mappings (greater than page-granularity) for all the memory bank rangs. + * In this scheme a comparatively quicker boot is observed. + * + * If ZONE_DMA configs are defined, crash kernel memory reservation + * is delayed until DMA zone memory range size initilazation performed in + * zone_sizes_init(). The defer is necessary to steer clear of DMA zone + * memory range to avoid overlap allocation. So crash kernel memory boundaries + * are not known when mapping all bank memory ranges, which otherwise means + * not possible to exclude crash kernel range from creating block mappings + * so page-granularity mappings are created for the entire memory range. + * Hence a slightly slower boot is observed. + * + * Note: Page-granularity mapppings are necessary for crash kernel memory + * range for shrinking its size via /sys/kernel/kexec_crash_size interface. */ -phys_addr_t arm64_dma_phys_limit __ro_after_init; +#if IS_ENABLED(CONFIG_ZONE_DMA) || IS_ENABLED(CONFIG_ZONE_DMA32) +phys_addr_t __ro_after_init arm64_dma_phys_limit; +#else +phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1; +#endif

#ifdef CONFIG_KEXEC_CORE /* @@ -210,8 +236,6 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max) if (!arm64_dma_phys_limit) arm64_dma_phys_limit = dma32_phys_limit; #endif - if (!arm64_dma_phys_limit) - arm64_dma_phys_limit = PHYS_MASK + 1; max_zone_pfns[ZONE_NORMAL] = max;

free_area_init(max_zone_pfns); @@ -407,6 +431,9 @@ void __init arm64_memblock_init(void)

reserve_elfcorehdr();

+ if (!IS_ENABLED(CONFIG_ZONE_DMA) && !IS_ENABLED(CONFIG_ZONE_DMA32)) + reserve_crashkernel(); + high_memory = __va(memblock_end_of_DRAM() - 1) + 1; }

@@ -451,7 +478,8 @@ void __init bootmem_init(void) * request_standard_resources() depends on crashkernel's memory being * reserved, so do it here. */ - reserve_crashkernel(); + if (IS_ENABLED(CONFIG_ZONE_DMA) || IS_ENABLED(CONFIG_ZONE_DMA32)) + reserve_crashkernel();

memblock_dump_all(); } diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 991e599f7057..993be1e31c49 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -492,7 +492,7 @@ static void __init map_mem(pgd_t *pgdp) int flags = 0; u64 i;

- if (rodata_full || crash_mem_map || debug_pagealloc_enabled()) + if (rodata_full || debug_pagealloc_enabled()) flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

/* @@ -503,6 +503,17 @@ static void __init map_mem(pgd_t *pgdp) */ memblock_mark_nomap(kernel_start, kernel_end - kernel_start);

+#ifdef CONFIG_KEXEC_CORE + if (crash_mem_map) { + if (IS_ENABLED(CONFIG_ZONE_DMA) || + IS_ENABLED(CONFIG_ZONE_DMA32)) + flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; + else if (crashk_res.end) + memblock_mark_nomap(crashk_res.start, + resource_size(&crashk_res)); + } +#endif + /* map all the memory banks */ for_each_mem_range(i, &start, &end) { if (start >= end) @@ -529,6 +540,25 @@ static void __init map_mem(pgd_t *pgdp) __map_memblock(pgdp, kernel_start, kernel_end, PAGE_KERNEL, NO_CONT_MAPPINGS); memblock_clear_nomap(kernel_start, kernel_end - kernel_start); + + /* + * Use page-level mappings here so that we can shrink the region + * in page granularity and put back unused memory to buddy system + * through /sys/kernel/kexec_crash_size interface. + */ +#ifdef CONFIG_KEXEC_CORE + if (crash_mem_map && + !IS_ENABLED(CONFIG_ZONE_DMA) && !IS_ENABLED(CONFIG_ZONE_DMA32)) { + if (crashk_res.end) { + __map_memblock(pgdp, crashk_res.start, + crashk_res.end + 1, + PAGE_KERNEL, + NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS); + memblock_clear_nomap(crashk_res.start, + resource_size(&crashk_res)); + } + } +#endif }

void mark_rodata_ro(void)