Re: [Xen-devel] [PATCH v2] arm/mem_access: don't reinject stage 2 access exceptions

[Julien Grall <julien.grall@xxxxxxx>]

Hi Tamas,

On 03/08/2016 11:13, Tamas K Lengyel wrote:
> The only way a guest may trip with stage 2 access violation is if mem_access is
> or was in-use, so reinjecting these exceptions to the guest is never required.
>
> Requested-by: Julien Grall <julien.grall@xxxxxxx>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

Regards,

> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
>
> v2: simplify the patch by never reinjecting the exception
> ---
>  xen/arch/arm/traps.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index f509a00..da951c0 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -2415,11 +2415,12 @@ static void do_trap_instr_abort_guest(struct 
> cpu_user_regs *regs,
>                  goto bad_insn_abort;
>          }
>
> -        rc = p2m_mem_access_check(gpa, gva, npfec);
> -
> -        /* Trap was triggered by mem_access, work here is done */
> -        if ( !rc )
> -            return;
> +        p2m_mem_access_check(gpa, gva, npfec);
> +        /*
> +         * The only way to get here right now is because of mem_access,
> +         * thus reinjecting the exception to the guest is never required.
> +         */
> +        return;
>      }
>      break;
>      }
> @@ -2462,11 +2463,12 @@ static void do_trap_data_abort_guest(struct 
> cpu_user_regs *regs,
>              .kind = dabt.s1ptw ? npfec_kind_in_gpt : npfec_kind_with_gla
>          };
>
> -        rc = p2m_mem_access_check(info.gpa, info.gva, npfec);
> -
> -        /* Trap was triggered by mem_access, work here is done */
> -        if ( !rc )
> -            return;
> +        p2m_mem_access_check(info.gpa, info.gva, npfec);
> +        /*
> +         * The only way to get here right now is because of mem_access,
> +         * thus reinjecting the exception to the guest is never required.
> +         */
> +        return;
>      }
>      break;
>      }
--
Julien Grall

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