From: bugzilla-daemon@kernel.org
To: kvm@vger.kernel.org
Subject: [Bug 216045] KVM x2APIC virtualization causes EOI to be ignored
Date: Sun, 29 May 2022 04:48:13 +0000 [thread overview]
Message-ID: <bug-216045-28872-VvH7MyoVHg@https.bugzilla.kernel.org/> (raw)
In-Reply-To: <bug-216045-28872@https.bugzilla.kernel.org/>
https://bugzilla.kernel.org/show_bug.cgi?id=216045
--- Comment #1 from Eric Li (ercli@ucdavis.edu) ---
Explanation of guest behavior
1. BIOS boots XMHF
2. XMHF starts GRUB as a nested guest
3. GRUB by default boots Debian (5 seconds timeout)
4. Debian executes 0xffffffff81062179 (can set a hardware breakpoint using
GDB). At this instruction is a WRMSR to 0x80b (IA32_X2APIC_EOI)
5. The WRMSR instruction above will VMEXIT to hypervisor mode (XMHF). The
VMEXIT entry point is 0x10206411 (xmhf_parteventhub_arch_x86vmx_entry)
6. At 0x10206434, the hypervisor calls 0x10207eb9
xmhf_parteventhub_arch_x86vmx_intercept_handler()
7. At 0x10208390, the hypervisor calls 0x10206d9f _vmx_handle_intercept_wrmsr()
8. At 0x102070c6, the hypervisor performs WRMSR to 0x80b. The intention is to
forward EOI from the guest (Debian) to KVM. Before WRMSR, "info lapic" in QEMU
gives
...
ISR 48
IRR 48
9. After WRMSR, RIP lands at 0x102070c8. "info lapic" in QEMU gives
...
ISR 48
IRR 48
However, I am expecting it to give
...
ISR (none)
IRR 48
10. After a lot of instructions, the nested Debian guest halts. "info lapic" is
...
ISR 236
IRR 48 236 253
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prev parent reply other threads:[~2022-05-29 4:48 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-29 4:26 [Bug 216045] New: KVM x2APIC virtualization causes EOI to be ignored bugzilla-daemon
2022-05-29 4:48 ` bugzilla-daemon [this message]
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