Messages in this thread Patch in this message | | | From | Alexandre Ghiti <> | Subject | [RFC PATCH 09/12] riscv: Allow user to downgrade to sv39 when hw supports sv48 | Date | Mon, 4 Jan 2021 14:58:37 -0500 |
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This is made possible by using the mmu-type property of the cpu node of the device tree.
By default, the kernel will boot with 4-level page table if the hw supports it but it can be interesting for the user to select 3-level page table as it is less memory consuming and faster since it requires less memory accesses in case of a TLB miss.
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr> Reviewed-by: Anup Patel <anup@brainfault.org> --- arch/riscv/mm/init.c | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index cb23a30d9af3..f9a99cb1870b 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -550,10 +550,32 @@ void disable_pgtable_l4(void) * then read SATP to see if the configuration was taken into account * meaning sv48 is supported. */ -asmlinkage __init void set_satp_mode(uintptr_t load_pa) +asmlinkage __init void set_satp_mode(uintptr_t load_pa, uintptr_t dtb_pa) { u64 identity_satp, hw_satp; + int cpus_node; + /* 1/ Check if the user asked for sv39 explicitly in the device tree */ + cpus_node = fdt_path_offset((void *)dtb_pa, "/cpus"); + if (cpus_node >= 0) { + int node; + + fdt_for_each_subnode(node, (void *)dtb_pa, cpus_node) { + const char *mmu_type = fdt_getprop((void *)dtb_pa, node, + "mmu-type", NULL); + if (!mmu_type) + continue; + + if (!strcmp(mmu_type, "riscv,sv39")) { + disable_pgtable_l4(); + return; + } + + break; + } + } + + /* 2/ Determine if the HW supports sv48: if not, fallback to sv39 */ create_pgd_mapping(early_pg_dir, load_pa, (uintptr_t)early_pud, PGDIR_SIZE, PAGE_TABLE); create_pud_mapping(early_pud, load_pa, (uintptr_t)early_pmd, @@ -611,7 +633,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) #endif #if defined(CONFIG_64BIT) && !defined(CONFIG_MAXPHYSMEM_2GB) - set_satp_mode(load_pa); + set_satp_mode(load_pa, dtb_pa); #endif kernel_virt_addr = KERNEL_VIRT_ADDR; -- 2.20.1
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