Re: [PATCH 2/2] riscv: Use PUD/PGDIR entries for linear mapping when possible

[Alex Ghiti]

Hi Atish,

Le 6/19/20 à 2:16 PM, Atish Patra a écrit :

On Thu, Jun 18, 2020 at 9:28 PM Alex Ghiti <a...@ghiti.fr> wrote:

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 <a...@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 <a...@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 ?

Not unless the remaining_size is at least page size aligned. The last
remaining size would "fff".
It will overflow as well after subtracting the map_size.

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

Yeah.

Thanks for noticing, I send a v2.

Alex

Thanks,

Alex

--
2.20.1