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

[Alex Ghiti]

Hi Atish,

Le 6/18/20 Ã 8:47 PM, Atish Patra a ÃcritÂ:
> On Wed, Jun 3, 2020 at 8:38 AM Alexandre Ghiti <alex@xxxxxxxx> 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@xxxxxxxx>
> > ---
> >   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