linux-kernel - disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a new stat)

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]

Message-ID: <03f2f5ab-e809-2ba5-bd98-3393c3b843d2@de.ibm.com>
Date:   Mon, 27 Sep 2021 09:22:49 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Matlack <dmatlack@...gle.com>,
        Jon Cargille <jcargill@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jing Zhang <jingzhangos@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Janosch Frank <frankja@...ux.ibm.com>
Subject: disabling halt polling broken? (was Re: [PATCH 00/14] KVM:
 Halt-polling fixes, cleanups and a new stat)

While looking into this series,

I realized that Davids patch

commit acd05785e48c01edb2c4f4d014d28478b5f19fb5
Author:     David Matlack <dmatlack@...gle.com>
AuthorDate: Fri Apr 17 15:14:46 2020 -0700
Commit:     Paolo Bonzini <pbonzini@...hat.com>
CommitDate: Fri Apr 24 12:53:17 2020 -0400

     kvm: add capability for halt polling

broke the possibility for an admin to disable halt polling for already running KVM guests.
In past times doing
echo 0 > /sys/module/kvm/parameters/halt_poll_ns

stopped polling system wide.
Now all KVM guests will use the halt_poll_ns value that was active during startup - even those that do not use KVM_CAP_HALT_POLL.

I guess this was not intended?