Messages in this thread Patch in this message | | | From | Jia He <> | Subject | [RFC PATCH 2/2] arm64: kpti: Update arm64_use_ng_mappings before pagetable mapping | Date | Wed, 13 Jan 2021 09:40:47 +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 previous commit moving init_cpu_features(), we can use cpu_have_const_cap earlier than before. Hence we can avoid this stall by updating arm64_use_ng_mappings.
Signed-off-by: Jia He <justin.he@arm.com> --- arch/arm64/kernel/setup.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c index e078ab068f3b..51098ceb7159 100644 --- a/arch/arm64/kernel/setup.c +++ b/arch/arm64/kernel/setup.c @@ -306,6 +306,10 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p) /* Init the cpu feature codes for boot cpu */ cpuinfo_store_boot_cpu(); + /* ARM64_UNMAP_KERNEL_AT_EL0 cap can be updated in cpuinfo_store_boot_cpu() */ + if (!arm64_use_ng_mappings) + arm64_use_ng_mappings = cpus_have_const_cap(ARM64_UNMAP_KERNEL_AT_EL0); + early_fixmap_init(); early_ioremap_init(); -- 2.17.1
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