[RFC PATCH 0/2] xapic: make sure x2APIC -> xapic transition correctly

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

The root cause is kvm_lapic_set_base() failing to handle x2APIC -> xapic ID
switch, which is addressed by patch 1.
Patch 2 provides a selftest to verify this behavior.

This serie is an RFC because I think that commit ef40757743b47 already tries to
fix one such effect of the error made in kvm_lapic_set_base, but I am not sure
how such error described in the commit message is triggered, nor how to
reproduce it using a selftest. I don't think one can enable/disable x2APIC using
KVM_SET_LAPIC, and kvm_lapic_set_base() in kvm_apic_set_state() just takes care
of updating apic->base_address, since value == old_value.
The test in patch 2 fails with the fix in ef40757743b47.

Thank you,
Emanuele

Emanuele Giuseppe Esposito (2):
  KVM: x86: update APIC_ID also when disabling x2APIC in
    kvm_lapic_set_base
  KVM: selftests: APIC_ID must be correctly updated when disabling
    x2apic

 arch/x86/kvm/lapic.c                          |  8 ++-
 .../selftests/kvm/x86_64/xapic_state_test.c   | 64 +++++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)

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2.31.1