linux-kernel - Re: [PATCH 1/6] powernv:idle: Correctly initialize core_idle_state

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 30 May 2017 15:53:24 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] powernv:idle: Correctly initialize
 core_idle_state_ptr

Hi Nicholas,

On Tue, May 30, 2017 at 03:56:12PM +1000, Nicholas Piggin wrote:
> On Tue, 16 May 2017 14:19:43 +0530
> "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> wrote:
> 
> > From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> > 
> > The lower 8 bits of core_idle_state_ptr tracks the number of non-idle
> > threads in the core. This is supposed to be initialized to bit-map
> > corresponding to the threads_per_core. However, currently it is
> > initialized to PNV_CORE_IDLE_THREAD_BITS (0xFF). This is correct for
> > POWER8 which has 8 threads per core, but not for POWER9 which has 4
> > threads per core.
> > 
> > As a result, on POWER9, core_idle_state_ptr gets initialized to
> > 0xFF. In case when all the threads of the core are idle, the bits
> > corresponding tracking the idle-threads are non-zero. As a result, the
> > idle entry/exit code fails to save/restore per-core hypervisor state
> > since it assumes that there are threads in the cores which are still
> > active.
> > 
> > Fix this by correctly initializing the lower bits of the
> > core_idle_state_ptr on the basis of threads_per_core.
> > 
> > Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> 
> This looks good to me.
> 
> Until this patch series, we can't enable HV state loss idle modes
> on POWER9, is that correct? And after your series does it work?

Yes, that is correct.

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

Thanks for reviewing the patch!

--
Thanks and Regards
gautham.