From: Segher Boessenkool <segher@kernel.crashing.org>
To: Laurent Dufour <ldufour@linux.ibm.com>
Cc: aik@ozlabs.ru, Ram Pai <linuxram@us.ibm.com>,
kvm-ppc@vger.kernel.org, bharata@linux.ibm.com,
sathnaga@linux.vnet.ibm.com, sukadev@linux.vnet.ibm.com,
linuxppc-dev@lists.ozlabs.org, bauerman@linux.ibm.com,
david@gibson.dropbear.id.au
Subject: Re: [RFC PATCH] powerpc/pseries/svm: capture instruction faulting on MMIO access, in sprg0 register
Date: Mon, 20 Jul 2020 15:10:41 -0500 [thread overview]
Message-ID: <20200720201041.GM30544@gate.crashing.org> (raw)
In-Reply-To: <18e3bcee-8a3a-bd13-c995-8e4168471f74@linux.ibm.com>
On Mon, Jul 20, 2020 at 11:39:56AM +0200, Laurent Dufour wrote:
> Le 16/07/2020 à 10:32, Ram Pai a écrit :
> >+ if (is_secure_guest()) { \
> >+ __asm__ __volatile__("mfsprg0 %3;" \
> >+ "lnia %2;" \
> >+ "ld %2,12(%2);" \
> >+ "mtsprg0 %2;" \
> >+ "sync;" \
> >+ #insn" %0,%y1;" \
> >+ "twi 0,%0,0;" \
> >+ "isync;" \
> >+ "mtsprg0 %3" \
> >+ : "=r" (ret) \
> >+ : "Z" (*addr), "r" (0), "r" (0) \
>
> I'm wondering if SPRG0 is restored to its original value.
> You're using the same register (r0) for parameters 2 and 3, so when doing
> lnia %2, you're overwriting the SPRG0 value you saved in r0 just earlier.
It is putting the value 0 in the registers the compiler chooses for
operands 2 and 3. But operand 3 is written, while the asm says it is an
input. It needs an earlyclobber as well.
> It may be clearer to use explicit registers for %2 and %3 and to mark them
> as modified for the compiler.
That is not a good idea, imnsho.
Segher
next prev parent reply other threads:[~2020-07-20 20:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 8:32 [RFC PATCH] powerpc/pseries/svm: capture instruction faulting on MMIO access, in sprg0 register Ram Pai
2020-07-20 9:39 ` Laurent Dufour
2020-07-20 20:10 ` Segher Boessenkool [this message]
2020-07-20 20:24 ` Segher Boessenkool
2020-07-21 7:22 ` Laurent Dufour
2020-07-21 15:00 ` Nicholas Piggin
2020-07-22 2:06 ` Michael Ellerman
2020-07-22 2:23 ` Benjamin Herrenschmidt
2020-07-22 7:49 ` Ram Pai
2020-07-22 12:45 ` Michael Ellerman
2020-07-24 11:49 ` Michael Ellerman
2020-07-22 5:02 ` Paul Mackerras
2020-07-22 7:42 ` Ram Pai
2020-07-22 7:45 ` Ram Pai
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