Re: [PATCH 4/7] RISC-V: Update page tables to cover the whole linear mapping

[Anup Patel]

On Thu, Mar 28, 2019 at 3:06 AM Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:
>
> With the new virtual address changes in an earlier patch, we want the
> page tables to cover more of the linear mapping region. Instead of
> only mapping from PAGE_OFFSET and up, we instead map starting
> from an aligned version of va_pa_offset such that all of the physical
> address space will be mapped.
>
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxx>
> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
> Cc: Anup Patel <anup.patel@xxxxxxx>
> Cc: Atish Patra <atish.patra@xxxxxxx>
> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> Cc: Zong Li <zongbox@xxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> ---
>  arch/riscv/kernel/setup.c |  1 -
>  arch/riscv/mm/init.c      | 27 +++++++++++++++------------
>  2 files changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index ecb654f6a79e..8286df8be31a 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -59,7 +59,6 @@ EXPORT_SYMBOL(empty_zero_page);
>  /* The lucky hart to first increment this variable will boot the other cores */
>  atomic_t hart_lottery;
>  unsigned long boot_cpu_hartid;
> -
>  void __init parse_dtb(unsigned int hartid, void *dtb)
>  {
>         if (early_init_dt_scan(__va(dtb)))
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index b9d50031e78f..315194557c3d 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -150,8 +150,8 @@ pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
>  pgd_t trampoline_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>
>  #ifndef __PAGETABLE_PMD_FOLDED
> -#define NUM_SWAPPER_PMDS ((uintptr_t)-PAGE_OFFSET >> PGDIR_SHIFT)
> -pmd_t swapper_pmd[PTRS_PER_PMD*((-PAGE_OFFSET)/PGDIR_SIZE)] __page_aligned_bss;
> +#define NUM_SWAPPER_PMDS ((uintptr_t)-VMALLOC_END >> PGDIR_SHIFT)
> +pmd_t swapper_pmd[PTRS_PER_PMD*((-VMALLOC_END)/PGDIR_SIZE)] __page_aligned_bss;
>  pmd_t trampoline_pmd[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>  pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
>  #endif
> @@ -180,13 +180,18 @@ asmlinkage void __init setup_vm(void)
>         extern char _start;
>         uintptr_t i;
>         uintptr_t pa = (uintptr_t) &_start;
> +       uintptr_t linear_start;
> +       uintptr_t off;
>         pgprot_t prot = __pgprot(pgprot_val(PAGE_KERNEL) | _PAGE_EXEC);
>
>         va_pa_offset = PAGE_OFFSET - pa;
>         pfn_base = PFN_DOWN(pa);
>
> +       linear_start = ALIGN_DOWN(va_pa_offset, PGDIR_SIZE);
> +       off = linear_start - va_pa_offset;
> +
>         /* Sanity check alignment and size */
> -       BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
> +       BUG_ON(linear_start <= VMALLOC_END);
>         BUG_ON((pa % (PAGE_SIZE * PTRS_PER_PTE)) != 0);
>
>  #ifndef __PAGETABLE_PMD_FOLDED
> @@ -195,15 +200,14 @@ asmlinkage void __init setup_vm(void)
>                         __pgprot(_PAGE_TABLE));
>         trampoline_pmd[0] = pfn_pmd(PFN_DOWN(pa), prot);
>
> -       for (i = 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
> -               size_t o = (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
> -
> +       for (i = 0; i < (-linear_start)/PGDIR_SIZE; ++i) {
> +               size_t o = (linear_start >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
>                 swapper_pg_dir[o] =
>                         pfn_pgd(PFN_DOWN((uintptr_t)swapper_pmd) + i,
>                                 __pgprot(_PAGE_TABLE));
>         }
>         for (i = 0; i < ARRAY_SIZE(swapper_pmd); i++)
> -               swapper_pmd[i] = pfn_pmd(PFN_DOWN(pa + i * PMD_SIZE), prot);
> +               swapper_pmd[i] = pfn_pmd(PFN_DOWN(off + i * PMD_SIZE), prot);
>
>         swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
>                 pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pmd),
> @@ -215,11 +219,10 @@ asmlinkage void __init setup_vm(void)
>         trampoline_pg_dir[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
>                 pfn_pgd(PFN_DOWN(pa), prot);
>
> -       for (i = 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
> -               size_t o = (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
> -
> -               swapper_pg_dir[o] =
> -                       pfn_pgd(PFN_DOWN(pa + i * PGDIR_SIZE), prot);
> +       for (i = 0; i < (-linear_start)/PGDIR_SIZE; ++i) {
> +               size_t o = (linear_start >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
> +               swapper_pg_dir[o] = pfn_pgd(PFN_DOWN(off + i * PGDIR_SIZE),
> +                                           prot);
>         }
>
>         swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
> --
> 2.20.1
>

I understand that this patch is inline with your virtual memory layout cleanup
but the way we map virtual memory in swapper_pg_dir is bound to change.

We should not be mapping complete virtual memory in swapper_pd_dir()
rather we should only map based on amount of RAM available.

Refer, https://www.lkml.org/lkml/2019/3/24/3

The setup_vm() should only map vmlinux_start to vmlinux_end plus the
FDT. Complete virtual memory mapping should be done after we have
done early parsing of FDT when we know available memory banks in
setup_vm_final() (called from paging_init())

Regards,
Anup