On 1/18/21 3:40 PM, Thomas Huth wrote:
> On 18/01/2021 15.03, Janosch Frank wrote:
>> On a program exception we usually skip the instruction that caused the
>> exception and continue. That won't work for UV calls since a "brc 3,0b"
>> will retry the instruction if the CC is > 1.
>>
>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>> ---
>>
>> I know this isn't very pretty.
>> I'm open for suggestions.
>>
>> ---
>> lib/s390x/asm/uv.h | 14 ++++++++------
>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/lib/s390x/asm/uv.h b/lib/s390x/asm/uv.h
>> index 4c2fc48..252f1a3 100644
>> --- a/lib/s390x/asm/uv.h
>> +++ b/lib/s390x/asm/uv.h
>> @@ -53,21 +53,23 @@ struct uv_cb_share {
>> static inline int uv_call(unsigned long r1, unsigned long r2)
>> {
>> int cc;
>> + struct lowcore *lc = 0x0;
>>
>> /*
>> - * The brc instruction will take care of the cc 2/3 case where
>> - * we need to continue the execution because we were
>> - * interrupted. The inline assembly will only return on
>> - * success/error i.e. cc 0/1.
>> - */
>> + * CC 2 and 3 tell us to re-execute because the instruction
>> + * hasn't yet finished.
>> + */
>> + lc->pgm_int_code = 0;
>> +retry:
>> asm volatile(
>> "0: .insn rrf,0xB9A40000,%[r1],%[r2],0,0\n"
>> - " brc 3,0b\n"
>> " ipm %[cc]\n"
>> " srl %[cc],28\n"
>> : [cc] "=d" (cc)
>> : [r1] "a" (r1), [r2] "a" (r2)
>> : "memory", "cc");
>> + if (!lc->pgm_int_code && cc > 1)
>> + goto retry;
>
> Why not simply:
>
> do {
> asm volatile(...);
> } while (!lc->pgm_int_code && cc > 1)
>
> ?
That would also be an option but it would basically be the same horrible
looking quick fix.
Claudio proposed implementing a one shot uv_call that doesn't branch
back. We should be able to use that purely for privilege checks.
>
> Thomas
>
