From: "Segher Boessenkool" <segher@kernel.crashing.org>
To: <Administrator@vger.kernel.org>
Cc: "linuxppc-dev list" <linuxppc-dev@lists.linuxppc.org>,
"Chris Friesen" <cfriesen@nortelnetworks.com>,
"Linux Kernel list" <linux-kernel@vger.kernel.org>
Subject: Re: want to clarify powerpc assembly conventions in head.S and entry.S
Date: Tue, 13 Apr 2004 16:45:53 +0100 [thread overview]
Message-ID: <000001c4216e$66eace80$d100000a@sbs2003.local> (raw)
In-Reply-To: <1081591559.25144.174.camel@gaston>
>> stwcx. r0,0,r1 /* to clear the reservation */
>>
>> I don't see the corresponding lwarx instruction. What reservation is
>> it
>> referring to?
>
> This is to clear any possible pending reservation if any. The problem
> is
> that the reservation mecanism only works accross multiple CPUs. A
> normal
> store at an address covered by a reservation on the same CPU will not
> break
> the reservation. Thus, to protect from that, any interrupt or exception
> makes sure to return to the normal code flow with any pending
> reservation
> cleared.
Worse, it is allowed for a PowerPC implementation to not check if
stwcx. and
stdcx. refer to the same address as the preceding lwarx or ldarx . So,
a store
conditional insn can succeed because the cpu holds some *other*
reservation.
Therefore, the kernel has to clear any reservation that might not have
been
generated by the user code it is returning to.
Segher
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2004-04-13 15:43 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-10 7:41 Chris Friesen
2004-04-10 10:05 ` Benjamin Herrenschmidt
2004-04-11 5:14 ` Chris Friesen
2004-04-11 5:25 ` Benjamin Herrenschmidt
2004-04-12 14:31 ` Chris Friesen
2004-04-12 22:54 ` Benjamin Herrenschmidt
2004-04-13 4:06 ` Chris Friesen
2004-04-13 4:31 ` Chris Friesen
2004-04-12 23:30 ` want to clarify powerpc assembly conventions inhead.S " Benjamin Herrenschmidt
2004-04-12 15:01 ` want to clarify powerpc assembly conventions in head.S " Chris Friesen
2004-04-11 6:00 ` want to clarify powerpc assembly conventions in head.Sand entry.S Benjamin Herrenschmidt
2004-04-11 5:45 ` want to clarify powerpc assembly conventions in head.S and entry.S Chris Friesen
2004-04-13 15:10 ` Segher Boessenkool
2004-04-13 15:45 ` Segher Boessenkool [this message]
2004-04-10 10:30 ` want to clarify powerpc assembly conventions in head.S andentry.S Benjamin Herrenschmidt
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