linux-kernel - Re: [PATCH v2 1/1] pseries/hotplug-cpu: Change default behaviour of cede

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] [day] [month] [year] [list]

Message-ID: <87k18klvxo.fsf@linux.ibm.com>
Date:   Thu, 31 Oct 2019 11:30:11 -0500
From:   Nathan Lynch <nathanl@...ux.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Kamalesh Babulal <kamaleshb@...ibm.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH v2 1/1] pseries/hotplug-cpu: Change default behaviour of cede_offline to "off"

"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> writes:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
>
> Currently on PSeries Linux guests, the offlined CPU can be put to one
> of the following two states:
>    - Long term processor cede (also called extended cede)
>    - Returned to the hypervisor via RTAS "stop-self" call.
>
> This is controlled by the kernel boot parameter "cede_offline=on/off".
>
> By default the offlined CPUs enter extended cede. The PHYP hypervisor
> considers CPUs in extended cede to be "active" since they are still
> under the control fo the Linux guests. Hence, when we change the SMT
> modes by offlining the secondary CPUs, the PURR and the RWMR SPRs will
> continue to count the values for offlined CPUs in extended cede as if
> they are online. This breaks the accounting in tools such as lparstat.
>
> To fix this, ensure that by default the offlined CPUs are returned to
> the hypervisor via RTAS "stop-self" call by changing the default value
> of "cede_offline_enabled" to false.
>
> Fixes: commit 3aa565f53c39 ("powerpc/pseries: Add hooks to put the CPU
> into an appropriate offline state")
>
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>

I'm OK with changing the default as a precursor to removing the code
that implements the cede offline mode.

Acked-by: Nathan Lynch <nathanl@...ux.ibm.com>