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authorChristian Krinitsin <mail@krinitsin.com>2025-06-01 21:35:14 +0200
committerChristian Krinitsin <mail@krinitsin.com>2025-06-01 21:35:14 +0200
commit3e4c5a6261770bced301b5e74233e7866166ea5b (patch)
tree9379fddaba693ef8a045da06efee8529baa5f6f4 /gitlab/issues_text/target_i386/host_missing/accel_KVM/2007
parente5634e2806195bee44407853c4bf8776f7abfa4f (diff)
downloadqemu-analysis-3e4c5a6261770bced301b5e74233e7866166ea5b.tar.gz
qemu-analysis-3e4c5a6261770bced301b5e74233e7866166ea5b.zip
clean up repository
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-Unable to update APIC_TPR when x2APIC is enabled and -global kvm-pit.lost_tick_policy=discard parameter provided
-Description of problem:
-I am developing a custom OS and I wanted to implement x2APIC support. I was able to enable x2APIC, read and write some registers, like APIC_VER and APIC_SIVR. Everything looks good, except that I cannot update APIC_TPR register. Reading it always returns 0. The code I wrote works properly on bare metal. Below some observations:
-
-Scenario 1:
-1. Enable x2APIC
-2. Write to CR8 - success
-3. Read from CR8 - gives correct value
-4. Read from APIC_TPR - gives correct value
-
-Scenario 2:
-1. Enable x2APIC
-2. Read from APIC_TPR - gives 0
-3. Write to APIC_TPR
-4. Read from APIC_TPR - gives 0 again
-
-Scenario 3:
-1. Initialize APIC (LAPIC or xAPIC)
-2. Write to APIC_TPR
-3. Read from APIC_TPR - gives correct value
-4. Switch to x2APIC
-5. Read from APIC_TPR - gives correct value stored in pt. 2
-6. Write to APIC_TPR
-7. Read from APIC_TPR - gives values stored in pt.2, not in point 6!
-
-Looks like APIC_TPR is stuck at value stored there before switching to x2APIC and it cannot be updated with MSR. Only update CR8 works.
-I have checked parameters I passed to qemu. After removing `-global kvm-pit.lost_tick_policy=discard` problem is gone and APIC_TPR is updated correctly.
-Additional information:
-Please let me know if you need additional information.