ACK: [SRU][N][PATCH 0/1] MultiVM - L2 guest(s) running stress-ng getting stuck at booting after triggering crash (LP: 2077722)

[Massimiliano Pellizzer]

On Wed, 29 Jan 2025 at 20:05, Tim Whisonant <tim.whisonant at canonical.com> wrote:
>
> On Wed, Jan 22, 2025 at 01:43:08PM +0100, frank.heimes at canonical.com wrote:
> > BugLink: https://bugs.launchpad.net/bugs/2077722
> >
> > SRU Justification:
> > ==================
> >
> > [Impact]
> >
> >  * L2 guest(s) (nested virtualization) running stress-ng getting stuck
> >    at booting after triggering crash.
> >
> >  * When for example having two Ubuntu 24.04 guests and running
> >    stress-ng (90% load) on both and triggering crash simultaneously,
> >    1st guest gets stuck and does not boot up.
> >
> >  * In one of the attempts, both the guests got stuck on booting with console hang.
> >
> > [Fix]
> >
> >  * a373830f96db a373830f96db288a3eb43a8692b6bcd0bd88dfe1
> >    "KVM: PPC: Book3S HV: Mask off LPCR_MER for a vCPU before running it to avoid spurious interrupts"
> >
> > [Test Plan]
> >
> >  * An Ubuntu Server 24.04 LPAR installation, acting as KVM host,
> >    on IBM Power 10 hardware (with nested KVM capable FW1060 or never) is needed.
> >
> >  * On top two (or more) KVM guests (now nested), again running 24.04,
> >    need to be setup.
> >
> >  * Run the attached stress-ng.sh script on both KVM guests.
> >
> >  * Trigger crash(es) on both KVM guests at the same time:
> >    echo c >/proc/sysrq-trigger
> >
> >  * At least one KVM guest (sometimes both) are now stuck while rebooting,
> >    without the above patch in place.
> >
> > [Where problems could occur]
> >
> >  * The changes are in arch/powerpc/kvm/book3s_hv.c only,
> >    hence are ppc specific and do not affect any other architecture.
> >
> >  * The net changes are more or less only two effective code lines;
> >    and additional else case and the explicit masking off the 'MER' bit.
> >
> >  * Wrong assumptions may have a different impact on KVM gusts (L0),
> >    or interfere with any other virtualization level.
> >
> >  * But the commit is an upstream accepted fix
> >    [for ec0f6639fa88 ("KVM: PPC: Book3S HV nestedv2: Ensure LPCR_MER bit is passed to the L0")]
> >    that landed in kernel 6.12 and was also accepted as stable update
> >    for kernels v6.8+.
> >
> > [Other Info]
> >
> >  * This fix/commit discussed here will be part of the planned
> >    target kernel for plucky, hence plucky/25.04 is not affected.
> >
> >  * The fix/commit is already included in oracular master-next
> >    as 08cbc81b9a61 and included starting with kernel Ubuntu-6.11.0-17.17.
> >
> >  * With that only noble needs to be fixed (since this nested virtualization
> >    scenario is not supported by Ubuntu prior to noble).
> >
> >  * Since the fix is upstream marked as stable update,
> >    it would usually be picked up by the kernel team automatically.
> >
> >  * But to not loose the 24.04.2 window out of sight I was asked
> >    to submit this patch separately.
> >
> > Gautam Menghani (1):
> >   KVM: PPC: Book3S HV: Mask off LPCR_MER for a vCPU before running it to
> >     avoid spurious interrupts
> >
> >  arch/powerpc/kvm/book3s_hv.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > --
> > 2.43.0
> >
>
> Acked-by: Tim Whisonant <tim.whisonant at canonical.com>
>
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
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Acked-by: Massimiliano Pellizzer <massimiliano.pellizzer at canonical.com>

-- 
Massimiliano Pellizzer