Re: [Qemu-devel] [PATCH] s390x/tcg: fixup TEST PROTECTION

[David Hildenbrand <david@redhat.com>]

On 12.01.2018 13:54, David Hildenbrand wrote:
> CC == 2 can only happen due to a protection exception, not if memory is
> not available (PGM_ADDRESSING). So all PGM_ADDRESSING exceptions have to
> be forwarded to the guest.
> 
> Since the initial definition of TEST PROTECTION, we now read globals
> (e.g. PSW mask), so we have to correctly mark the instruction
> (otherwise, e.g. booting fedora 27 fails).
> 
> Also, the architecture explicitly specifies which exceptions are
> forwarded to the guest, this makes the code a little nicer.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  target/s390x/cpu.h        |  2 ++
>  target/s390x/helper.h     |  2 +-
>  target/s390x/EM_helper.c | 41 +++++++++++++++++++----------------------
>  3 files changed, 22 insertions(+), 23 deletions(-)
> 
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index 1a8b6b9ae9..915bccbc75 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -759,6 +759,8 @@ int s390_cpu_virt_mem_rw(S390CPU *cpu, vaddr laddr, uint8_t ar, void *hostbuf,
>          s390_cpu_virt_mem_rw(cpu, laddr, ar, dest, len, false)
>  #define s390_cpu_virt_mem_write(cpu, laddr, ar, dest, len)       \
>          s390_cpu_virt_mem_rw(cpu, laddr, ar, dest, len, true)
> +#define s390_cpu_virt_mem_check_read(cpu, laddr, ar, len)   \
> +        s390_cpu_virt_mem_rw(cpu, laddr, ar, NULL, len, false)
>  #define s390_cpu_virt_mem_check_write(cpu, laddr, ar, len)   \
>          s390_cpu_virt_mem_rw(cpu, laddr, ar, NULL, len, true)
>  void s390_cpu_virt_mem_handle_exc(S390CPU *cpu, uintptr_t ra);
> diff --git a/target/s390x/helper.h b/target/s390x/helper.h
> index 26c1b07b44..59a1d9869b 100644
> --- a/target/s390x/helper.h
> +++ b/target/s390x/helper.h
> @@ -137,7 +137,7 @@ DEF_HELPER_FLAGS_4(lctlg, TCG_CALL_NO_WG, void, env, i32, i64, i32)
>  DEF_HELPER_FLAGS_4(stctl, TCG_CALL_NO_WG, void, env, i32, i64, i32)
>  DEF_HELPER_FLAGS_4(stctg, TCG_CALL_NO_WG, void, env, i32, i64, i32)
>  DEF_HELPER_FLAGS_2(testblock, TCG_CALL_NO_WG, i32, env, i64)
> -DEF_HELPER_FLAGS_3(tprot, TCG_CALL_NO_RWG, i32, env, i64, i64)
> +DEF_HELPER_FLAGS_3(tprot, TCG_CALL_NO_WG, i32, env, i64, i64)
>  DEF_HELPER_FLAGS_2(iske, TCG_CALL_NO_RWG_SE, i64, env, i64)
>  DEF_HELPER_FLAGS_3(sske, TCG_CALL_NO_RWG, void, env, i64, i64)
>  DEF_HELPER_FLAGS_2(rrbe, TCG_CALL_NO_RWG, i32, env, i64)
> diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
> index 359e446c6f..c957febc6d 100644
> --- a/target/s390x/mem_helper.c
> +++ b/target/s390x/mem_helper.c
> @@ -1730,34 +1730,31 @@ uint32_t HELPER(tprot)(CPUS390XState *env, uint64_t a1, uint64_t a2)
>          /* Fetching permitted; storing permitted */
>          return 0;
>      }
> +
> +    if (env->int_pgm_code == PGM_PROTECTION) {
> +        /* retry if reading is possible */
> +        cs->exception_index = 0;
> +        if (!s390_cpu_virt_mem_check_read(cpu, a1, 0, 1)) {
> +            /* Fetching permitted; storing not permitted */
> +            return 1;
> +        }
> +    }
> +
>      switch (env->int_pgm_code) {
>      case PGM_PROTECTION:
> -        /* Fetching permitted; storing not permitted */
> -        cs->exception_index = 0;
> -        return 1;
> -    case PGM_ADDRESSING:
>          /* Fetching not permitted; storing not permitted */
>          cs->exception_index = 0;
>          return 2;
> -    case PGM_ASCE_TYPE:
> -    case PGM_REG_FIRST_TRANS:
> -    case PGM_REG_SEC_TRANS:
> -    case PGM_REG_THIRD_TRANS:
> -    case PGM_SEGMENT_TRANS:
> -    case PGM_PAGE_TRANS:
> -    case PGM_ALET_SPEC:
> -    case PGM_ALEN_SPEC:
> -    case PGM_ALE_SEQ:
> -    case PGM_ASTE_VALID:
> -    case PGM_ASTE_SEQ:
> -    case PGM_EXT_AUTH:
> -        /* Translation not available */
> -        cs->exception_index = 0;
> -        return 3;
> +    case PGM_ADDRESSING:
> +    case PGM_TRANS_SPEC:
> +        /* exceptions forwarded to the guest */
> +        s390_cpu_virt_mem_handle_exc(cpu, GETPC());
> +        return 0;
>      }
> -    /* any other exception is forwarded to the guest */
> -    s390_cpu_virt_mem_handle_exc(cpu, GETPC());
> -    return 0;
> +
> +    /* Translation not available */
> +    cs->exception_index = 0;
> +    return 3;
>  }
>  
>  /* insert storage key extended */
> 

Ping, this is certainly better than the current (queued) state. Would
love to see some review. But if nobody volunteers to read the PoP, I
think my current use case (Linux and kvm-unit-tests) have to be
sufficient for now.

-- 

Thanks,

David / dhildenb