[PATCH 0/3] x86/x2apic: Fix hang-up of defconfig kernel on resume from s2ram

[Shashank Balaji <shashank.mahadasyam@sony.com>]

On resume from s2ram, a defconfig kernel gets into a state where the x2apic
hardware state and the kernel's perceived state are different.

On boot, x2apic is enabled by the firmware, and then the kernel does the
following (relevant lines from dmesg):

	[    0.000381] x2apic: enabled by BIOS, switching to x2apic ops
	[    0.009939] APIC: Switched APIC routing to: cluster x2apic
	[    0.095151] x2apic: IRQ remapping doesn't support X2APIC mode
	[    0.095154] x2apic disabled
	[    0.095551] APIC: Switched APIC routing to: physical flat

defconfig has CONFIG_IRQ_REMAP=n, which leads to x2apic being disabled,
because on bare metal, x2apic has an architectural dependence on interrupt
remapping.

While resuming from s2ram, x2apic is enabled again by the firmware, but
the kernel continues using the physical flat apic routing. This causes a
hang-up and no console output.

Patch 1 fixes this in lapic_resume by disabling x2apic when the kernel expects
it to be disabled.
Patch 2 enables CONFIG_IRQ_REMAP in defconfig so that defconfig kernels at
least don't disable x2apic because of a lack of IRQ_REMAP support.
Patch 3 is a non-functional change renaming x2apic_available to
x2apic_without_ir_available in struct x86_hyper_init, to better convey
the semantic.

Signed-off-by: Rahul Bukte <rahul.bukte@sony.com>
Signed-off-by: Shashank Balaji <shashank.mahadasyam@sony.com>
---
Shashank Balaji (3):
      x86/x2apic: disable x2apic on resume if the kernel expects so
      x86/defconfig: add CONFIG_IRQ_REMAP
      x86/virt: rename x2apic_available to x2apic_without_ir_available

 arch/x86/configs/x86_64_defconfig |  1 +
 arch/x86/include/asm/x86_init.h   |  4 ++--
 arch/x86/kernel/apic/apic.c       | 10 ++++++++--
 arch/x86/kernel/cpu/acrn.c        |  2 +-
 arch/x86/kernel/cpu/bhyve.c       |  2 +-
 arch/x86/kernel/cpu/mshyperv.c    |  2 +-
 arch/x86/kernel/cpu/vmware.c      |  2 +-
 arch/x86/kernel/jailhouse.c       |  2 +-
 arch/x86/kernel/kvm.c             |  2 +-
 arch/x86/kernel/x86_init.c        | 12 ++++++------
 arch/x86/xen/enlighten_hvm.c      |  4 ++--
 11 files changed, 25 insertions(+), 18 deletions(-)
---
base-commit: 18f7fcd5e69a04df57b563360b88be72471d6b62
change-id: 20260201-x2apic-fix-85c8c1b5cb90

Best regards,
-- 
Shashank Balaji <shashank.mahadasyam@sony.com>