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

[Sean Christopherson]

On Mon, 09 Jan 2023 08:06:03 -0500, Emanuele Giuseppe Esposito wrote:
> 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.
> 
> [...]

Applied to kvm-x86 apic, with the tweak of only stuffing the APIC_ID if the
APIC is enabled.  I also heavily reworked the testcase (see feedback on that
patch).

Thanks!

[1/2] KVM: x86: Reinitialize xAPIC ID when userspace forces x2APIC => xAPIC
      https://github.com/kvm-x86/linux/commit/052c3b99cbc8
[2/2] KVM: selftests: Verify APIC_ID is set when forcing x2APIC=>xAPIC transition
      https://github.com/kvm-x86/linux/commit/eb9819257631

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes