KVM: x86: Fix lapic timer interrupt lost after loading a snapshot.
When running android emulator (which is based on QEMU 2.12) on certain Intel hosts with kernel version 6.3-rc1 or above, guest will freeze after loading a snapshot. This is almost 100% reproducible. By default, the android emulator will use snapshot to speed up the next launching of the same android guest. So this breaks the android emulator badly. I tested QEMU 8.0.4 from Debian 12 with an Ubuntu 22.04 guest by running command "loadvm" after "savevm". The same issue is observed. At the same time, none of our AMD platforms is impacted. More experiments show that loading the KVM module with "enable_apicv=false" can workaround it. The issue started to show up after commit 8e6ed96c ("KVM: x86: fire timer when it is migrated and expired, and in oneshot mode"). However, as is pointed out by Sean Christopherson, it is introduced by commit 967235d3 ("KVM: vmx: clear pending interrupts on KVM_SET_LAPIC"). commit 8e6ed96c ("KVM: x86: fire timer when it is migrated and expired, and in oneshot mode") just makes it easier to hit the issue. Having both commits, the oneshot lapic timer gets fired immediately inside the KVM_SET_LAPIC call when loading the snapshot. On Intel platforms with APIC virtualization and posted interrupt processing, this eventually leads to setting the corresponding PIR bit. However, the whole PIR bits get cleared later in the same KVM_SET_LAPIC call by apicv_post_state_restore. This leads to timer interrupt lost. The fix is to move vmx_apicv_post_state_restore to the beginning of the KVM_SET_LAPIC call and rename to vmx_apicv_pre_state_restore. What vmx_apicv_post_state_restore does is actually clearing any former apicv state and this behavior is more suitable to carry out in the beginning. Fixes: 967235d3 ("KVM: vmx: clear pending interrupts on KVM_SET_LAPIC") Cc: stable@vger.kernel.org Suggested-by:Sean Christopherson <seanjc@google.com> Signed-off-by:
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