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SubjectRe: [PATCH 2/2] riscv: Use PUD/PGDIR entries for linear mapping when possible
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Hi Atish,

Le 6/18/20 à 8:47 PM, Atish Patra a écrit :
> 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.

I'm not sure I understand: if pa starts at 0x8000_0000 and size is 2G,
then pa will overflow in the last iteration, but remaining_size will
then be equal to 0 right ?

And by the way, I realize that this loop only handles sizes that are
aligned on map_size.

Thanks,

Alex


>
>> --
>> 2.20.1
>>
>>
>

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