Re: [Qemu-devel] [RFC PATCH] target-s390x: Implement mvcos instruction

[Thomas Huth <thuth@redhat.com>]

On 28.02.2017 14:17, Miroslav Benes wrote:
> Implement MVCOS instruction, which the Linux kernel uses in user access
> functions.
> 
> Signed-off-by: Miroslav Benes <mbenes@suse.cz>
> ---
> I tried to do my best to follow the specification but it is quite
> possible that I got something wrong because of my lack of
> understanding. Especially I am not sure about all those bit ops :/.
> 
> Anyway, there is one piece missing. The actual use of keys and
> address-space-control during the move. I used fast_memmove, but
> it is not correct. Is there a helper which I could use? I looked at
> other instructions which should implement access control, but there were
> silently ignore it :).

I'm not aware of a function that could deal with two address spaces
already (but that does not mean that there is no such function already)
... still, I guess, you likely need to write your own memmove helper
function that can deal with two different address spaces.

>  target/s390x/helper.h      |  1 +
>  target/s390x/insn-data.def |  2 ++
>  target/s390x/mem_helper.c  | 80 ++++++++++++++++++++++++++++++++++++++++++++++
>  target/s390x/translate.c   | 12 +++++++
>  4 files changed, 95 insertions(+)
> 
> diff --git a/target/s390x/helper.h b/target/s390x/helper.h
> index 9102071d0aa4..bc5dfccc3d7e 100644
> --- a/target/s390x/helper.h
> +++ b/target/s390x/helper.h
> @@ -104,6 +104,7 @@ 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)
>  DEF_HELPER_3(csp, i32, env, i32, i64)
> +DEF_HELPER_5(mvcos, i32, env, i64, i64, i64, i64)
>  DEF_HELPER_4(mvcs, i32, env, i64, i64, i64)
>  DEF_HELPER_4(mvcp, i32, env, i64, i64, i64)
>  DEF_HELPER_4(sigp, i32, env, i64, i32, i64)
> diff --git a/target/s390x/insn-data.def b/target/s390x/insn-data.def
> index 075ff597c3de..a1e6d735d090 100644
> --- a/target/s390x/insn-data.def
> +++ b/target/s390x/insn-data.def
> @@ -854,6 +854,8 @@
>  /* LOAD USING REAL ADDRESS */
>      C(0xb24b, LURA,    RRE,   Z,   0, r2, new, r1_32, lura, 0)
>      C(0xb905, LURAG,   RRE,   Z,   0, r2, r1, 0, lurag, 0)
> +/* MOVE WITH OPTIONAL SPECIFICATION */
> +    C(0xc800, MVCOS,   SSF,   MVCOS, la1, a2, 0, 0, mvcos, 0)
>  /* MOVE TO PRIMARY */
>      C(0xda00, MVCP,    SS_d,  Z,   la1, a2, 0, 0, mvcp, 0)
>  /* MOVE TO SECONDARY */
> diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
> index 675aba2e44d4..ca8f7c49250c 100644
> --- a/target/s390x/mem_helper.c
> +++ b/target/s390x/mem_helper.c
> @@ -1089,6 +1089,86 @@ uint32_t HELPER(mvcp)(CPUS390XState *env, uint64_t l, uint64_t a1, uint64_t a2)
>      return cc;
>  }
>  
> +uint32_t HELPER(mvcos)(CPUS390XState *env, uint64_t r0, uint64_t dest,
> +                       uint64_t src, uint64_t len)
> +{
> +    int cc;
> +    int key1, as1, abit1, kbit1;
> +    int key2, as2, abit2, kbit2;
> +
> +    HELPER_LOG("%s dest %" PRIx64 ", src %" PRIx64 ", len %" PRIx64 "\n",
> +               __func__, dest, src, len);
> +
> +    /* check DAT */
> +    if (!(env->psw.mask & PSW_MASK_DAT)) {
> +        program_interrupt(env, PGM_SPECIAL_OP, 2);

Length of the opcode is 6 bytes, not 2.

> +    }
> +
> +    /* access control for the first operand */
> +    abit1 = (r0 & 0x0010000ULL) >> 16;
> +    kbit1 = (r0 & 0x0020000ULL) >> 17;
> +    as1 = (r0 & 0x00c00000ULL) >> 22;
> +    key1 = (r0 & 0xf0000000ULL) >> 28;
> +
> +    if (!kbit1) {
> +        key1 = (env->psw.mask & PSW_MASK_KEY) >> (PSW_SHIFT_KEY - 4);

I wonder whether it would make sense to define PSW_SHIFT_KEY directly to
52 instead ... I can't see the reason for 56 here. The only other spot
that uses it also subtracts 4.

> +    }
> +
> +    if (!abit1) {
> +        as1 = (env->psw.mask & PSW_MASK_ASC) >> 46;
> +    }
> +
> +    /*
> +     * abit1 is set, as1 designates the home-space mode, psw is in the problem
> +     * state.
> +     * */

Cosmetic nit: Make the closing comment just "*/" instead of "* */".

> +    if (abit1 && (as1 == 3) && (env->psw.mask & PSW_MASK_PSTATE)) {
> +        program_interrupt(env, PGM_SPECIAL_OP, 2);

set instruction length = 6 again

> +    }
> +
> +    /* access control for the second operand */
> +    abit2 = (r0 & 0x0010000ULL);
> +    kbit2 = (r0 & 0x0020000ULL) >> 1;
> +    as2 = (r0 & 0x00c00000ULL) >> 6;
> +    key2 = (r0 & 0xf0000000ULL) >> 12;

The above four lines look wrong ... are you sure that you've got the
masks right? If I read the POP correctly, the values should be in the
lowest two bytes instead?

> +    if (!kbit2) {
> +        key2 = (env->psw.mask & PSW_MASK_KEY) >> (PSW_SHIFT_KEY - 4);
> +    }
> +
> +    if (!abit2) {
> +        as2 = (env->psw.mask & PSW_MASK_ASC) >> 46;
> +    }
> +
> +    /*
> +     * Secondary-space control bit is zero (bit 37 of r0) and either as
> +     * designates secondary-space mode.
> +     */
> +    if (!(r0 & 0x2000000000ULL) && (as1 == 2 || as2 == 2)) {

You mixed up "control register 0" with "general purpose register 0"
here, i.e. you must not use r0 but rather env->cregs[0] here.

> +        program_interrupt(env, PGM_SPECIAL_OP, 2);

s/2/6/

> +    }
> +
> +    /* psw is in the problem state and either key is invalid */
> +    if ((env->psw.mask & PSW_MASK_PSTATE) &&
> +        (!(env->cregs[3] & (1 << (31 - key1))) ||
> +         !(env->cregs[3] & (1 << (31 - key2))))) {
> +        program_interrupt(env, PGM_PRIVILEGED, 2);

s/2/6/

> +    }
> +
> +    if (len <= 4096) {
> +        cc = 0;
> +    } else {
> +        cc = 3;
> +        len = 4096;
> +    }
> +
> +    /* move */
> +    /* XXX use keys and as during the move */
> +    fast_memmove(env, dest, src, len);
> +
> +    return cc;
> +}
> +
>  /* invalidate pte */
>  void HELPER(ipte)(CPUS390XState *env, uint64_t pte_addr, uint64_t vaddr)
>  {
> diff --git a/target/s390x/translate.c b/target/s390x/translate.c
> index 01c62176bf70..ac90b758d312 100644
> --- a/target/s390x/translate.c
> +++ b/target/s390x/translate.c
> @@ -1194,6 +1194,7 @@ typedef enum DisasFacility {
>      FAC_SCF,                /* store clock fast */
>      FAC_SFLE,               /* store facility list extended */
>      FAC_ILA,                /* interlocked access facility 1 */
> +    FAC_MVCOS,              /* move-with-optional-specification */
>  } DisasFacility;
>  
>  struct DisasInsn {
> @@ -2877,6 +2878,17 @@ static ExitStatus op_mvcs(DisasContext *s, DisasOps *o)
>      set_cc_static(s);
>      return NO_EXIT;
>  }
> +
> +static ExitStatus op_mvcos(DisasContext *s, DisasOps *o)
> +{
> +    int r3 = get_field(s->fields, r3);
> +
> +    check_privileged(s);

I think it is possible to use this instruction in PRoblem state, so the
general check_privileged() check seems to be wrong here. The instruction
only generates a PRIVILEGE exception if the keys are invalid.

> +    potential_page_fault(s);
> +    gen_helper_mvcos(cc_op, cpu_env, regs[0], o->addr1, o->in2, regs[r3]);
> +    set_cc_static(s);
> +    return NO_EXIT;
> +}
>  #endif
>  
>  static ExitStatus op_mvpg(DisasContext *s, DisasOps *o)
>