Re: [PATCH] riscv: Fix Stage2 SV32 page table walk

[Alistair Francis]

On Mon, Mar 30, 2020 at 1:28 AM Anup Patel <address@hidden> wrote:
>
> As-per RISC-V H-Extension v0.5 draft, the Stage2 SV32 page table has
> 12bits of VPN[1] and 10bits of VPN[0]. The additional 2bits in VPN[1]
> is required to handle the 34bit intermediate physical address coming
> from Stage1 SV32 page table. The 12bits of VPN[1] implies that Stage2
> SV32 level-0 page table will be 16KB in size with total 4096 enteries
> where each entry maps 4MB of memory (same as Stage1 SV32 page table).
>
> The get_physical_address() function is broken for Stage2 SV32 level-0
> page table because it incorrectly computes output physical address for
> Stage2 SV32 level-0 page table entry.
>
> The root cause of the issue is that get_physical_address() uses the
> "widened" variable to compute level-0 physical address mapping which
> changes level-0 mapping size (instead of 4MB). We should use the
> "widened" variable only for computing index of Stage2 SV32 level-0
> page table.
>
> Signed-off-by: Anup Patel <address@hidden>

Reviewed-by: Alistair Francis <address@hidden>

Alistair

> ---
>  target/riscv/cpu_helper.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 50e13a064f..bc80aa87cf 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -559,12 +559,7 @@ restart:
>              /* for superpage mappings, make a fake leaf PTE for the TLB's
>                 benefit. */
>              target_ulong vpn = addr >> PGSHIFT;
> -            if (i == 0) {
> -                *physical = (ppn | (vpn & ((1L << (ptshift + widened)) - 
> 1))) <<
> -                             PGSHIFT;
> -            } else {
> -                *physical = (ppn | (vpn & ((1L << ptshift) - 1))) << PGSHIFT;
> -            }
> +            *physical = (ppn | (vpn & ((1L << ptshift) - 1))) << PGSHIFT;
>
>              /* set permissions on the TLB entry */
>              if ((pte & PTE_R) || ((pte & PTE_X) && mxr)) {
> --
> 2.17.1
>
>