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

[Alex Ghiti]

Hi Atish,

Le 6/22/20 Ã 3:11 PM, Atish Patra a ÃcritÂ:
> On Sun, Jun 21, 2020 at 2:39 AM Alex Ghiti <alex@xxxxxxxx> wrote:
> > Hi Atish,
> >
> > Le 6/20/20 Ã 5:04 AM, Alex Ghiti a Ãcrit :
> > > Hi Atish,
> > >
> > > Le 6/19/20 Ã 2:16 PM, Atish Patra a Ãcrit :
> > > > On Thu, Jun 18, 2020 at 9:28 PM Alex Ghiti <alex@xxxxxxxx> wrote:
> > > > > Hi Atish,
> > > > >
> > > > > Le 6/18/20 Ã 8:47 PM, Atish Patra a Ãcrit :
> > > > > > 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 ?
> > > > 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.
> >
> >
> > While fixing this issue, I noticed that if the size in the device tree
> > is not aligned on PAGE_SIZE, the size is then automatically realigned on
> > PAGE_SIZE: see early_init_dt_add_memory_arch where size is and-ed with
> > PAGE_MASK to remove the unaligned part.
> Yes. But the memblock size is not guaranteed to be PAGE_SIZE aligned.
> The memblock size is updated in memblock_cap_size
>
>      /* adjust *@size so that (@base + *@size) doesn't overflow, return
> new size */
>     static inline phys_addr_t memblock_cap_size(phys_addr_t base,
> phys_addr_t *size)
>     {
>              return *size = min(*size, PHYS_ADDR_MAX - base);
>     }

Yes you're right, I will fix that in a v2.

Thanks,

Alex

> You will not see this issue right away even if you allocate 2GB of
> memory while running 32 bit linux in qemu
> because the kernel removes anything beyond 0xc0400000 for 32 bit in
> bootmem setup.
>
> â[    0.000000][    T0] memblock_remove: [0xc0400000-0xfffffffe]
> setup_bootmem+0x90/0x216
>
> This also restricts the kernel to use only 1GB of memory even if
> maximum physical memory supported is 2GB.
>
> > So the issue does not need to be fixed :)
> >
> > Thanks anyway,
> >
> > Alex
> >
> >
> > > > > 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
>
>
>
> --
> Regards,
> Atish