Re: [PATCH V3] target/riscv: Bugfix reserved bits in PTE for RV64

[Alistair Francis]

On Tue, Sep 24, 2019 at 9:48 PM <address@hidden> wrote:
>
> From: Guo Ren <address@hidden>
>
> Highest 10 bits of PTE are reserved in riscv-privileged, ref: [1], so we
> need to ignore them. They can not be a part of ppn.
>
> 1: The RISC-V Instruction Set Manual, Volume II: Privileged Architecture
>    4.4 Sv39: Page-Based 39-bit Virtual-Memory System
>    4.5 Sv48: Page-Based 48-bit Virtual-Memory System

Hey,

As I mentioned on patch 2 I don't think this is right. It isn't up to
HW to clear these bits, software should keep them clear.

Alistair

>
> Signed-off-by: Guo Ren <address@hidden>
> Reviewed-by: Liu Zhiwei <address@hidden>
> ---
>  target/riscv/cpu_bits.h   | 3 +++
>  target/riscv/cpu_helper.c | 4 +++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> ---
> Changelog V3:
>  - Use UUL define for PTE_RESERVED.
>  - Keep ppn >> PTE_PPN_SHIFT
>
> Changelog V2:
>  - Bugfix pte destroyed cause boot fail
>  - Change to AND with a mask instead of shifting both directions
>
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index e998348..cdc62a8 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -470,6 +470,9 @@
>  #define PTE_D               0x080 /* Dirty */
>  #define PTE_SOFT            0x300 /* Reserved for Software */
>
> +/* Reserved highest 10 bits in PTE */
> +#define PTE_RESERVED        0xFFC0000000000000ULL
> +
>  /* Page table PPN shift amount */
>  #define PTE_PPN_SHIFT       10
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 87dd6a6..7e04ff5 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -258,10 +258,12 @@ restart:
>          }
>  #if defined(TARGET_RISCV32)
>          target_ulong pte = ldl_phys(cs->as, pte_addr);
> +        hwaddr ppn = pte;
>  #elif defined(TARGET_RISCV64)
>          target_ulong pte = ldq_phys(cs->as, pte_addr);
> +        hwaddr ppn = pte & ~PTE_RESERVED;
>  #endif
> -        hwaddr ppn = pte >> PTE_PPN_SHIFT;
> +        ppn = ppn >> PTE_PPN_SHIFT;
>
>          if (!(pte & PTE_V)) {
>              /* Invalid PTE */
> --
> 2.7.4
>