[email protected] (Eric W. Biederman) writes: > [email protected] (Eric W. Biederman) writes: > >> Baoquan He <[email protected]> writes: >> >>> On kvm guest, kernel always prints warning during kdump kernel boots as >>> below. >>> >>> [ 0.001000] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/apic/apic.c:1467 >>> setup_local_APIC+0x228/0x330 >>> [ 0.001000] Modules linked in: >>> [ 0.001000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-rc5+ #3 >>> [ 0.001000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS >>> 1.10.2-1.fc26 04/01/2014 >>> [ 0.001000] RIP: 0010:setup_local_APIC+0x228/0x330 >>> [ 0.001000] RSP: 0000:ffffffffb6e03eb8 EFLAGS: 00010286 >>> [ 0.001000] RAX: 0000009edb4c4d84 RBX: 0000000000000000 RCX: >>> 00000000b099d800 >>> [ 0.001000] RDX: 0000009e00000000 RSI: 0000000000000000 RDI: >>> 0000000000000810 >>> [ 0.001000] RBP: 0000000000000000 R08: ffffffffffffffff R09: >>> 0000000000000001 >>> [ 0.001000] R10: ffff98ce6a801c00 R11: 0761076d072f0776 R12: >>> 0000000000000001 >>> [ 0.001000] R13: 00000000000000f0 R14: 0000000000004000 R15: >>> ffffffffffffc6ff >>> [ 0.001000] FS: 0000000000000000(0000) GS:ffff98ce6bc00000(0000) >>> knlGS:0000000000000000 >>> [ 0.001000] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [ 0.001000] CR2: 00000000ffffffff CR3: 0000000022209000 CR4: >>> 00000000000406b0 >>> [ 0.001000] Call Trace: >>> [ 0.001000] apic_bsp_setup+0x56/0x74 >>> [ 0.001000] x86_late_time_init+0x11/0x16 >>> [ 0.001000] start_kernel+0x3c9/0x486 >>> [ 0.001000] secondary_startup_64+0xa5/0xb0 >>> [ 0.001000] Code: 00 85 c9 74 2d 0f 31 c1 e1 0a 48 c1 e2 20 41 89 cf 4c >>> 03 7c 24 08 48 09 d0 49 29 c7 4c 89 3c 24 48 83 3c 24 00 0f 8f 8f fe ff >>> ff <0f> ff e9 10 ff ff ff 48 83 2c 24 01 eb e7 48 83 c4 18 5b 5d 41 >>> [ 0.001000] ---[ end trace b88e71b9a6ebebdd ]--- >>> [ 0.001000] masked ExtINT on CPU#0 >>> >>> The root cause is the legacy irq mode is disabled before jump to kexec/kdump >>> kernel since commit 522e66464467 ("x86/apic: Disable I/O APIC before >>> shutdown >>> of the local APIC"). In that commit, lapic_shutdown() calling was moved >>> after >>> disable_IO_APIC(). In fact in disable_IO_APIC(), it not only calls >>> clear_IO_APIC() to disable IO-APIC, and also sets LAPIC and IO-APIC to make >>> system be PIC or Virtual wire mode. Hence local APIC is disabled completely >>> by the calling of lapic_shutdown(). >> >> The actions of lapic_shutdown do not depend on the actions of >> disable_IO_APIC so this description and justificaiton are nonsense. >> >> Further we don't hardware disable the local APIC except when we hardware >> enable it. And only on 32bit at that. >> >> I keep wondering if the above oops is due to an emulation bug in kvm. >> If that is the case it might be better to fix kvm. > > Sigh. Reading a little deeper I see where the local apic is affected. > It is the work of disconnect_bsp_APIC called from disable_IO_APIC. > > Calling lapic_shutdown (which clears the local apic) after the local > apic has been placed into virtual wire mode would indeed be a problem. > > Now that I see that I agree in essence with this patch series. > I don't agree with the implemenation details. > > Can you please split disable_IO_APIC and switch_to_legacy_irq_mode > in a single patch.
Now that I think about it can you call the function not switch_to_legacy_irq_mode but restore_boot_irq_mode. And the corresponding x86_io_apic_ops not .disable but .restore. That should make the purpose of the code clearer, and help avoid mistakes like the one that led to this regression. Eric
