Messages in this thread | | | From | Jia He <> | Subject | [RFC PATCH 0/2] Avoid booting stall caused by | Date | Wed, 13 Jan 2021 09:40:45 +0800 |
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There is a 10s stall in idmap_kpti_install_ng_mappings when kernel boots on a Ampere EMAG server.
Commit f992b4dfd58b ("arm64: kpti: Add ->enable callback to remap swapper using nG mappings") updates the nG bit runtime if kpti is required.
But things get worse if rodata=full in map_mem(). NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS is required when creating pagetable mapping. Hence all ptes are fully mapped in this case. On a Ampere EMAG server with 256G memory(pagesize=4k), it causes the 10s stall.
After moving init_cpu_features() ahead of early_fixmap_init(), we can use cpu_have_const_cap earlier than before. Hence we can avoid this stall by updating arm64_use_ng_mappings.
After this patch series, it reduces the kernel boot time from 14.7s to 4.1s: Before: [ 14.757569] Freeing initrd memory: 60752K After: [ 4.138819] Freeing initrd memory: 60752K
Set it as RFC because I want to resolve any other points which I have misconerned.
Jia He (2): arm64/cpuinfo: Move init_cpu_features() ahead of early_fixmap_init() arm64: kpti: Update arm64_use_ng_mappings before pagetable mapping
arch/arm64/include/asm/cpu.h | 1 + arch/arm64/kernel/cpuinfo.c | 13 ++++++++++--- arch/arm64/kernel/setup.c | 18 +++++++++++++----- arch/arm64/kernel/smp.c | 3 +-- 4 files changed, 25 insertions(+), 10 deletions(-)
-- 2.17.1
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