Re: [PATCH v2] target/riscv: Add proper two-stage lookup exception detection

[Alistair Francis]

On Fri, Mar 19, 2021 at 10:16 AM Georg Kotheimer
<georg.kotheimer@kernkonzept.com> wrote:
>
> The current two-stage lookup detection in riscv_cpu_do_interrupt falls
> short of its purpose, as all it checks is whether two-stage address
> translation either via the hypervisor-load store instructions or the
> MPRV feature would be allowed.
>
> What we really need instead is whether two-stage address translation was
> active when the exception was raised. However, in riscv_cpu_do_interrupt
> we do not have the information to reliably detect this. Therefore, when
> we raise a memory fault exception we have to record whether two-stage
> address translation is active.
>
> Signed-off-by: Georg Kotheimer <georg.kotheimer@kernkonzept.com>

Thanks!

Applied to riscv-to-apply.next

Alistair

> ---
> Unfortunately, I tested the previous version of the patch only against
> the RISC-V softmmu target, not against the linux-user target.
> I modified the patch, so that the two_stage_lookup is neither present
> nor updated for the linux-user target.
>
>  target/riscv/cpu.c        |  1 +
>  target/riscv/cpu.h        |  4 ++++
>  target/riscv/cpu_helper.c | 21 ++++++++-------------
>  3 files changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index ddea8fbeeb..e8c4455525 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -356,6 +356,7 @@ static void riscv_cpu_reset(DeviceState *dev)
>      env->mstatus &= ~(MSTATUS_MIE | MSTATUS_MPRV);
>      env->mcause = 0;
>      env->pc = env->resetvec;
> +    env->two_stage_lookup = false;
>  #endif
>      cs->exception_index = EXCP_NONE;
>      env->load_res = -1;
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 0edb2826a2..0a33d387ba 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -213,6 +213,10 @@ struct CPURISCVState {
>      target_ulong satp_hs;
>      uint64_t mstatus_hs;
>
> +    /* Signals whether the current exception occurred with two-stage address
> +       translation active. */
> +    bool two_stage_lookup;
> +
>      target_ulong scounteren;
>      target_ulong mcounteren;
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 2f43939fb6..af00728829 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -605,6 +605,7 @@ static void raise_mmu_exception(CPURISCVState *env, 
> target_ulong address,
>          g_assert_not_reached();
>      }
>      env->badaddr = address;
> +    env->two_stage_lookup = two_stage;
>  }
>
>  hwaddr riscv_cpu_get_phys_page_debug(CPUState *cs, vaddr addr)
> @@ -646,6 +647,8 @@ void riscv_cpu_do_transaction_failed(CPUState *cs, hwaddr 
> physaddr,
>      }
>
>      env->badaddr = addr;
> +    env->two_stage_lookup = riscv_cpu_virt_enabled(env) ||
> +                            riscv_cpu_two_stage_lookup(mmu_idx);
>      riscv_raise_exception(&cpu->env, cs->exception_index, retaddr);
>  }
>
> @@ -669,6 +672,8 @@ void riscv_cpu_do_unaligned_access(CPUState *cs, vaddr 
> addr,
>          g_assert_not_reached();
>      }
>      env->badaddr = addr;
> +    env->two_stage_lookup = riscv_cpu_virt_enabled(env) ||
> +                            riscv_cpu_two_stage_lookup(mmu_idx);
>      riscv_raise_exception(env, cs->exception_index, retaddr);
>  }
>  #endif /* !CONFIG_USER_ONLY */
> @@ -910,16 +915,8 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>          /* handle the trap in S-mode */
>          if (riscv_has_ext(env, RVH)) {
>              target_ulong hdeleg = async ? env->hideleg : env->hedeleg;
> -            bool two_stage_lookup = false;
>
> -            if (env->priv == PRV_M ||
> -                (env->priv == PRV_S && !riscv_cpu_virt_enabled(env)) ||
> -                (env->priv == PRV_U && !riscv_cpu_virt_enabled(env) &&
> -                    get_field(env->hstatus, HSTATUS_HU))) {
> -                    two_stage_lookup = true;
> -            }
> -
> -            if ((riscv_cpu_virt_enabled(env) || two_stage_lookup) && 
> write_tval) {
> +            if (env->two_stage_lookup && write_tval) {
>                  /*
>                   * If we are writing a guest virtual address to stval, set
>                   * this to 1. If we are trapping to VS we will set this to 0
> @@ -957,10 +954,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>                  riscv_cpu_set_force_hs_excep(env, 0);
>              } else {
>                  /* Trap into HS mode */
> -                if (!two_stage_lookup) {
> -                    env->hstatus = set_field(env->hstatus, HSTATUS_SPV,
> -                                             riscv_cpu_virt_enabled(env));
> -                }
> +                env->hstatus = set_field(env->hstatus, HSTATUS_SPV, false);
>                  htval = env->guest_phys_fault_addr;
>              }
>          }
> @@ -1016,6 +1010,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>       * RISC-V ISA Specification.
>       */
>
> +    env->two_stage_lookup = false;
>  #endif
>      cs->exception_index = EXCP_NONE; /* mark handled to qemu */
>  }
> --
> 2.31.0
>
>