From: Heiko Carstens <hca@linux.ibm.com>
To: Nico Boehr <nrb@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>,
kvm@vger.kernel.org, linux-s390@vger.kernel.org,
imbrenda@linux.ibm.com, thuth@redhat.com, david@redhat.com,
nsg@linux.ibm.com
Subject: Re: [kvm-unit-tests RFC 2/2] lib: s390x: css: Name inline assembly arguments and clean them up
Date: Mon, 22 Apr 2024 12:57:20 +0200 [thread overview]
Message-ID: <20240422105720.31205-A-hca@linux.ibm.com> (raw)
In-Reply-To: <171377182433.14316.15188579220205837716@t14-nrb>
On Mon, Apr 22, 2024 at 09:43:44AM +0200, Nico Boehr wrote:
> Quoting Janosch Frank (2024-02-01 15:23:56)
> [...]
> > diff --git a/lib/s390x/css.h b/lib/s390x/css.h
> > index 504b3f14..e4311124 100644
> > --- a/lib/s390x/css.h
> > +++ b/lib/s390x/css.h
> [...]
> > @@ -167,11 +167,11 @@ static inline int msch(unsigned long schid, struct schib *addr)
> > int cc;
> >
> > asm volatile(
> > - " msch 0(%3)\n"
> > - " ipm %0\n"
> > - " srl %0,28"
> > - : "=d" (cc)
> > - : "d" (reg1), "m" (*addr), "a" (addr)
> > + " msch 0(%[addr])\n"
> > + " ipm %[cc]\n"
> > + " srl %[cc],28"
> > + : [cc] "=d" (cc)
> > + : "d" (reg1), [addr] "a" (addr)
>
> I think there was a reason why the "m"(*addr) was here. Either add it back
> or add a memory clobber.
It is there to tell the compiler that the memory contents at *addr are used
as input. Without that, and only the "a" contraint, the compiler is free to
discard any potential previous writes to *addr.
The best solution here would be to use the Q constraint (memory reference
with short displacement and without index register) for the second operand
address of msch. Or simply copy the current implementation from the kernel
(drivers/s390/cio/ioasm.c).
prev parent reply other threads:[~2024-04-22 10:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-01 14:23 [kvm-unit-tests RFC 0/2] lib: s390x: Inline asm cleanup Janosch Frank
2024-02-01 14:23 ` [kvm-unit-tests RFC 1/2] lib: s390x: sigp: Name inline assembly arguments Janosch Frank
2024-02-01 17:52 ` Claudio Imbrenda
2024-02-01 14:23 ` [kvm-unit-tests RFC 2/2] lib: s390x: css: Name inline assembly arguments and clean them up Janosch Frank
2024-04-22 7:43 ` Nico Boehr
2024-04-22 10:57 ` Heiko Carstens [this message]
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