From: Nathan Lynch <nathanl@linux.ibm.com>
To: Leonardo Bras <leonardo@linux.ibm.com>
Cc: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>,
Paul Mackerras <paulus@samba.org>, Nadav Amit <namit@vmware.com>,
Thomas Gleixner <tglx@linutronix.de>,
linuxppc-dev@lists.ozlabs.org,
Allison Randal <allison@lohutok.net>
Subject: Re: [PATCH 1/1] powerpc/rtas: Implement reentrant rtas call
Date: Thu, 14 May 2020 14:04:55 -0500 [thread overview]
Message-ID: <875zcy2v8o.fsf@linux.ibm.com> (raw)
In-Reply-To: <ba97d52df60ac9c4a4afc2c03121a8c263aa5a15.camel@linux.ibm.com>
Hi Leonardo,
Leonardo Bras <leonardo@linux.ibm.com> writes:
> Hello Nathan, thanks for the feedback!
>
> On Fri, 2020-04-10 at 14:28 -0500, Nathan Lynch wrote:
>> Leonardo Bras <leonardo@linux.ibm.com> writes:
>> > Implement rtas_call_reentrant() for reentrant rtas-calls:
>> > "ibm,int-on", "ibm,int-off",ibm,get-xive" and "ibm,set-xive".
>> >
>> > On LoPAPR Version 1.1 (March 24, 2016), from 7.3.10.1 to 7.3.10.4,
>> > items 2 and 3 say:
>> >
>> > 2 - For the PowerPC External Interrupt option: The * call must be
>> > reentrant to the number of processors on the platform.
>> > 3 - For the PowerPC External Interrupt option: The * argument call
>> > buffer for each simultaneous call must be physically unique.
>> >
>> > So, these rtas-calls can be called in a lockless way, if using
>> > a different buffer for each call.
>> >
>
>> From the language in the spec it's clear that these calls are intended
>> to be reentrant with respect to themselves, but it's less clear to me
>> that they are safe to call simultaneously with respect to each other or
>> arbitrary other RTAS methods.
>
> In my viewpoint, being reentrant to themselves, without being reentrant
> to others would be very difficult to do, considering the way the
> rtas_call is crafted to work.
>
> I mean, I have no experience in rtas code, it's my viewpoint. In my
> thoughts there is something like this:
>
> common_path -> selects function by token -> reentrant function
> |-> non-reentrant function
>
> If there is one function that is reentrant, it means the common_path
> and function selection by token would need to be reentrant too.
I checked with partition firmware development and these calls can be
used concurrently with arbitrary other RTAS calls, which confirms your
interpretation. Thanks for bearing with me.
next prev parent reply other threads:[~2020-05-14 19:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-08 22:39 [PATCH 1/1] powerpc/rtas: Implement reentrant rtas call Leonardo Bras
2020-04-10 19:28 ` Nathan Lynch
2020-05-13 4:31 ` Leonardo Bras
2020-05-14 19:04 ` Nathan Lynch [this message]
2020-05-14 20:22 ` Leonardo Bras
2020-05-13 5:23 ` Leonardo Bras
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