Re: [Qemu-devel] [PATCHv3 1/5] RISC-V: Only Check PMP if MMU translation succeeds

[Alistair Francis <alistair23@gmail.com>]

On Tue, May 21, 2019 at 3:44 AM Hesham Almatary
<Hesham.Almatary@cl.cam.ac.uk> wrote:
>
> The current implementation unnecessarily checks for PMP even if MMU translation
> failed. This may trigger a wrong PMP access exception instead of
> a page exception.
>
> For example, the very first instruction fetched after the first satp write in
> S-Mode will trigger a PMP access fault instead of an instruction fetch page
> fault.
>
> This patch prioritises MMU exceptions over PMP exceptions and only checks for
> PMP if MMU translation succeeds.

It's probably worth noting in the commit message that this commit is
only required for the future commits. Otherwise it is a little
confusing.

Alistair

>
> Signed-off-by: Hesham Almatary <Hesham.Almatary@cl.cam.ac.uk>
> ---
>  target/riscv/cpu_helper.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 41d6db41c3..40fb47e794 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -401,6 +401,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
>                    " prot %d\n", __func__, address, ret, pa, prot);
>
>      if (riscv_feature(env, RISCV_FEATURE_PMP) &&
> +        (ret == TRANSLATE_SUCCESS) &&
>          !pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type)) {
>          ret = TRANSLATE_FAIL;
>      }
> --
> 2.17.1
>
>