Re: [Qemu-devel] [PATCH-for-4.2 v1 1/9] s390x/mmu: Better ASC selection in s390_cpu_get_phys_page_debug()

[Cornelia Huck <cohuck@redhat.com>]

On Mon,  5 Aug 2019 17:29:39 +0200
David Hildenbrand <david@redhat.com> wrote:

> Let's select the ASC before calling the function and use MMU_DATA_LOAD.
> This is a preparation to:
> - Remove the ASC magic depending on the access mode from mmu_translate
> - Implement IEP support, where we could run into access exceptions

'IEP' was instruction execution protection?

>   trying to fetch instructions
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  target/s390x/helper.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/target/s390x/helper.c b/target/s390x/helper.c
> index 13ae9909ad..08166558a0 100644
> --- a/target/s390x/helper.c
> +++ b/target/s390x/helper.c
> @@ -58,7 +58,15 @@ hwaddr s390_cpu_get_phys_page_debug(CPUState *cs, vaddr vaddr)
>          vaddr &= 0x7fffffff;
>      }
>  
> -    if (mmu_translate(env, vaddr, MMU_INST_FETCH, asc, &raddr, &prot, false)) {
> +    /*
> +     * We want to read the code, however, not run into access exceptions
> +     * (especially, IEP).
> +     */
> +    if (asc != PSW_ASC_HOME) {
> +        asc = PSW_ASC_PRIMARY;
> +    }

Previously, if we'd go in here specifying access register mode, we'd
hw_error() out. Now, that would be rewritten to using primary. Could
that be a problem, or do we filter out access register mode even
earlier?

(As an aside, I'm not sure the guest crashing qemu by specifying access
register mode was a good idea. Or do we get to slap the guest before
that happens?)

> +
> +    if (mmu_translate(env, vaddr, MMU_DATA_LOAD, asc, &raddr, &prot, false)) {
>          return -1;
>      }
>      return raddr;