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SubjectRe: [PATCH 6/8] riscv: Allow user to downgrade to sv39 when hw supports sv48
On Sun, May 24, 2020 at 2:46 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> 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>
> ---
> arch/riscv/mm/init.c | 25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index bad8da099ff6..1776eeb53d61 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -509,11 +509,32 @@ 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,
> @@ -561,7 +582,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> load_sz = (uintptr_t)(&_end) - load_pa;
>
> #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
>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

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