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SubjectRe: [PATCH 2/2] riscv: Use PUD/PGDIR entries for linear mapping when possible
On Wed, Jun 3, 2020 at 8:38 AM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> Improve best_map_size so that PUD or PGDIR entries are used for linear
> mapping when possible as it allows better TLB utilization.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
> arch/riscv/mm/init.c | 45 +++++++++++++++++++++++++++++++++-----------
> 1 file changed, 34 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 9a5c97e091c1..d275f9f834cf 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -424,13 +424,29 @@ static void __init create_pgd_mapping(pgd_t *pgdp,
> create_pgd_next_mapping(nextp, va, pa, sz, prot);
> }
>
> -static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
> +static bool is_map_size_ok(uintptr_t map_size, phys_addr_t base,
> + uintptr_t base_virt, phys_addr_t size)
> {
> - /* Upgrade to PMD_SIZE mappings whenever possible */
> - if ((base & (PMD_SIZE - 1)) || (size & (PMD_SIZE - 1)))
> - return PAGE_SIZE;
> + return !((base & (map_size - 1)) || (base_virt & (map_size - 1)) ||
> + (size < map_size));
> +}
> +
> +static uintptr_t __init best_map_size(phys_addr_t base, uintptr_t base_virt,
> + phys_addr_t size)
> +{
> +#ifndef __PAGETABLE_PMD_FOLDED
> + if (is_map_size_ok(PGDIR_SIZE, base, base_virt, size))
> + return PGDIR_SIZE;
> +
> + if (pgtable_l4_enabled)
> + if (is_map_size_ok(PUD_SIZE, base, base_virt, size))
> + return PUD_SIZE;
> +#endif
> +
> + if (is_map_size_ok(PMD_SIZE, base, base_virt, size))
> + return PMD_SIZE;
>
> - return PMD_SIZE;
> + return PAGE_SIZE;
> }
>
> /*
> @@ -576,7 +592,7 @@ void create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> {
> uintptr_t va, end_va;
> - uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
> + uintptr_t map_size;
>
> load_pa = (uintptr_t)(&_start);
> load_sz = (uintptr_t)(&_end) - load_pa;
> @@ -587,6 +603,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>
> kernel_virt_addr = KERNEL_VIRT_ADDR;
>
> + map_size = best_map_size(load_pa, PAGE_OFFSET, MAX_EARLY_MAPPING_SIZE);
> va_pa_offset = PAGE_OFFSET - load_pa;
> va_kernel_pa_offset = kernel_virt_addr - load_pa;
> pfn_base = PFN_DOWN(load_pa);
> @@ -700,6 +717,8 @@ static void __init setup_vm_final(void)
>
> /* Map all memory banks */
> for_each_memblock(memory, reg) {
> + uintptr_t remaining_size;
> +
> start = reg->base;
> end = start + reg->size;
>
> @@ -707,15 +726,19 @@ static void __init setup_vm_final(void)
> break;
> if (memblock_is_nomap(reg))
> continue;
> - if (start <= __pa(PAGE_OFFSET) &&
> - __pa(PAGE_OFFSET) < end)
> - start = __pa(PAGE_OFFSET);
>
> - map_size = best_map_size(start, end - start);
> - for (pa = start; pa < end; pa += map_size) {
> + pa = start;
> + remaining_size = reg->size;
> +
> + while (remaining_size) {
> va = (uintptr_t)__va(pa);
> + map_size = best_map_size(pa, va, remaining_size);
> +
> create_pgd_mapping(swapper_pg_dir, va, pa,
> map_size, PAGE_KERNEL);
> +
> + pa += map_size;
> + remaining_size -= map_size;
> }
> }
>

This may not work in the RV32 with 2G memory and if the map_size is
determined to be a page size
for the last memblock. Both pa & remaining_size will overflow and the
loop will try to map memory from zero again.

> --
> 2.20.1
>
>


--
Regards,
Atish

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