linux-kernel - Re: powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline

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Message-Id: <3xyKGW0mggz9s78@ozlabs.org>
Date:   Thu, 21 Sep 2017 11:46:43 +1000 (AEST)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Pavithra Prakash <pavirampu@...ux.vnet.ibm.com>
Cc:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline

On Thu, 2017-08-31 at 11:47:41 UTC, "Gautham R. Shenoy" wrote:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via
> stop-api only on Hotplug") clears the PECE1 bit of the LPCR via
> stop-api during CPU-Hotplug to prevent wakeup due to a decrementer on
> an offlined CPU which is in a deep stop state.
> 
> In the case where the stop-api support is found to be lacking, the
> commit 785a12afdb4a ("powerpc/powernv/idle: Disable LOSE_FULL_CONTEXT
> states when stop-api fails") disables deep states that lose hypervisor
> context. Thus in this case, the offlined CPU will be put to some
> shallow idle state.
> 
> However, we currently unconditionally clear the PECE1 in LPCR via
> stop-api during CPU-Hotplug even when deep states are disabled due to
> stop-api failure.
> 
> Fix this by clearing PECE1 of LPCR via stop-api during CPU-Hotplug
> *only* when the offlined CPU will be put to a deep state that loses
> hypervisor context.
> 
> Fixes: commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via
> stop-api only on Hotplug")
> 
> Reported-by: Pavithra Prakash <pavirampu@...ux.vnet.ibm.com>
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> Reviewed-by: Nicholas Piggin <npiggin@...il.com>
> Tested-by: Pavithra Prakash <pavrampu@...ux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/5d298baa41883fc421acfd932799c0

cheers