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
