linux-kernel - Re: [v3 PATCH 4/4] powernv: Recover correct PACA on wakeup from a stop on P9 DD1

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Message-ID: <20170323020628.56b40eed@roar.ozlabs.ibm.com>
Date:   Thu, 23 Mar 2017 02:06:28 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "Shreyas B. Prabhu" <shreyasbp@...il.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Anton Blanchard <anton@...ba.org>,
        Balbir Singh <bsingharora@...il.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH 4/4] powernv: Recover correct PACA on wakeup from a
 stop on P9 DD1

On Wed, 22 Mar 2017 20:34:17 +0530
"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> wrote:

> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> POWER9 DD1.0 hardware has an issue due to which the SPRs of a thread
> waking up from stop 0,1,2 with ESL=1 can endup being misplaced in the
> core. Thus the HSPRG0 of a thread waking up from can contain the paca
> pointer of its sibling.
> 
> This patch implements a context recovery framework within threads of a
> core, by provisioning space in paca_struct for saving every sibling
> threads's paca pointers. Basically, we should be able to arrive at the
> right paca pointer from any of the thread's existing paca pointer.
> 
> At bootup, during powernv idle-init, we save the paca address of every
> CPU in each one its siblings paca_struct in the slot corresponding to
> this CPU's index in the core.
> 
> On wakeup from a stop, the thread will determine its index in the core
> from the TIR register and recover its PACA pointer by indexing into
> the correct slot in the provisioned space in the current PACA.
> 
> Furthermore, ensure that the NVGPRs are restored from the stack on the
> way out by setting the NAPSTATELOST in paca.
> 
> [Changelog written with inputs from svaidy@...ux.vnet.ibm.com]

Looks good.

Reviewed-by: Nicholas Piggin <npiggin@...il.com>