[PATCH v3 13/13] riscv: Allow user to downgrade to sv39 when hw supports sv48 if !KASAN
From: Alexandre Ghiti <hidden>
Date: 2021-12-06 11:00:37
Also in:
linux-arch, linux-efi, linux-riscv, lkml
Subsystem:
risc-v architecture, the rest · Maintainers:
Paul Walmsley, Palmer Dabbelt, Albert Ou, Linus Torvalds
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. This functionality requires that kasan is disabled since calling the fdt functions that are kasan instrumented with the MMU off can't work. Signed-off-by: Alexandre Ghiti <redacted> --- arch/riscv/mm/init.c | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 28de6ea0a720..299b5a44f902 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c@@ -633,10 +633,38 @@ static void __init disable_pgtable_l4(void) * then read SATP to see if the configuration was taken into account * meaning sv48 is supported. */ -static __init void set_satp_mode(void) +static __init void set_satp_mode(uintptr_t dtb_pa) { u64 identity_satp, hw_satp; uintptr_t set_satp_mode_pmd; +#ifndef CONFIG_KASAN + /* + * The below fdt functions are kasan instrumented, since at this point + * there is no mapping for the kasan shadow memory, this can't be used + * when kasan is enabled otherwise it traps. + */ + int cpus_node; + + /* 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; + } + } +#endif set_satp_mode_pmd = ((unsigned long)set_satp_mode) & PMD_MASK; create_pgd_mapping(early_pg_dir,
@@ -838,7 +866,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) #endif #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL) - set_satp_mode(); + set_satp_mode(dtb_pa); #endif kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
--
2.32.0