[PATCH v3] arm64: Do not defer reserve_crashkernel() for platforms with no DMA memory zones

From: Vijay Balakrishna
Date: Wed Mar 02 2022 - 12:38:23 EST

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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@xxxxxxxxxxxxxxxxxxx/

Signed-off-by: Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Changes from v2 -> v3
---------------------
- IS_ENABLED() does not need to be an #ifdef (Mike's comment)

[v2] https://lore.kernel.org/all/1645646253-16072-1-git-send-email-vijayb@xxxxxxxxxxxxxxxxxxx/

Changes from v1 -> v2
---------------------
- replaced '!crashk_res.end' with IS_ENABLED(ZONE_DMA/DMA32) (Nicolas's comment)
- minor change to make it uniform -- replaced #if defined(..) -> #if IS_ENABLED(..)
- added new comment in arch/arm64/mm/init.c to ease future maintenance (Nicolas's comment)
- test performed comment moved to commit message

[v1] https://lore.kernel.org/all/1645056294-6509-1-git-send-email-vijayb@xxxxxxxxxxxxxxxxxxx/
---
arch/arm64/mm/init.c | 36 ++++++++++++++++++++++++++++++++----
arch/arm64/mm/mmu.c | 28 +++++++++++++++++++++++++++-
2 files changed, 59 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index db63cc885771..9e26ec80d317 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -61,8 +61,34 @@ 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
/*
@@ -153,8 +179,6 @@ 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);
@@ -315,6 +339,9 @@ void __init arm64_memblock_init(void)

early_init_fdt_scan_reserved_mem();

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

@@ -361,7 +388,8 @@ 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 acfae9b41cc8..b32c0fb40ef7 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -517,7 +517,7 @@ static void __init map_mem(pgd_t *pgdp)
*/
BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end));

- if (can_set_direct_map() || crash_mem_map || IS_ENABLED(CONFIG_KFENCE))
+ if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE))
flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

/*
@@ -528,6 +528,15 @@ static void __init map_mem(pgd_t *pgdp)
*/
memblock_mark_nomap(kernel_start, kernel_end - kernel_start);

+ if (IS_ENABLED(CONFIG_KEXEC_CORE) && 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));
+ }
+
/* map all the memory banks */
for_each_mem_range(i, &start, &end) {
if (start >= end)
@@ -554,6 +563,23 @@ 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.
+ */
+ if (IS_ENABLED(CONFIG_KEXEC_CORE) && 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));
+ }
+ }
}

void mark_rodata_ro(void)
--
2.35.1

Next message: Rob Herring: "Re: [PATCH v6 3/3] dt-bindings: soundwire: qcom: Add bindings for audio CSR reset control property"
Previous message: Sean Christopherson: "Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous worker"
Next in thread: Pasha Tatashin: "Re: [PATCH v3] arm64: Do not defer reserve_crashkernel() for platforms with no DMA memory zones"
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