linux-kernel - [PATCH v2 0/2] x86/apic: reset LDR in clear_local

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Date:   Mon, 26 Aug 2019 06:15:11 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/2] x86/apic: reset LDR in clear_local_APIC

v2:
   1/2: clear out the bogus initialization in bigsmp_init_apic_ldr
   2/2: reword commit message as suggested by Thomas
v1 posted at https://lkml.org/lkml/2019/8/14/1

On a 32 bit RHEL6 guest with greater than 8 cpus, the
kdump kernel hangs when calibrating apic. This happens
because when apic initializes bigsmp, it also initializes LDR
even though it probably wouldn't be used.

When booting into kdump, KVM apic incorrectly reads the stale LDR
values from the guest while building the logical destination map
even for inactive vcpus. While KVM apic can be fixed to ignore apics
that haven't been enabled, a simple guest only change can be to
just clear out the LDR.

Bandan Das (2):
  x86/apic: Do not initialize LDR and DFR for bigsmp
  x86/apic: include the LDR when clearing out apic registers

 arch/x86/kernel/apic/apic.c      |  4 ++++
 arch/x86/kernel/apic/bigsmp_32.c | 24 ++----------------------
 2 files changed, 6 insertions(+), 22 deletions(-)

-- 
2.20.1