On 12/09/2011 05:15 PM, Alexander Graf wrote: > > On 09.12.2011, at 20:15, Scott Wood wrote: > >> On 12/09/2011 01:10 PM, Alexander Graf wrote: >>> >>> On 09.12.2011, at 19:19, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote: >>> >>>> On 12/09/2011 09:26 AM, Alexander Graf wrote: >>>>> Our vcpu kick implementation differs a bit from x86 which resulted in us not >>>>> disabling preemption during the kick. Get it a bit closer to what x86 does. >>>> >>>> Disabling preemption only matters due to the other bit of functionality >>>> you brought over -- avoiding kicking the current CPU. >>> >>> Nope, I had BUG_ON warnings in the kick code because preemption was on. >> >> Coming from where? > > From here: > > BUG: using smp_processor_id() in preemptible [00000000] code: qemu-system-ppc/17448 > caller is .smp_mpic_message_pass+0x88/0x10c > Call Trace: > [c000000078d83600] [c000000000013e70] .show_stack+0x6c/0x16c (unreliable) > [c000000078d836b0] [c00000000037b614] .debug_smp_processor_id+0xe4/0x11c > [c000000078d83740] [c000000000048988] .smp_mpic_message_pass+0x88/0x10c > [c000000078d837d0] [c00000000002f2b4] .smp_send_reschedule+0x4c/0x80 > [c000000078d83850] [d000000005e68984] .kvm_vcpu_kick+0x5c/0x74 [kvm] > [c000000078d838d0] [d000000005e689d8] .kvm_vcpu_ioctl_interrupt+0x3c/0x54 [kvm] > [c000000078d83950] [d000000005e68a8c] .kvm_arch_vcpu_ioctl+0x9c/0x21c [kvm] > [c000000078d83b60] [d000000005e64520] .kvm_vcpu_ioctl+0x7c/0x6b8 [kvm] > [c000000078d83c20] [d000000005e64c2c] .kvm_vcpu_compat_ioctl+0xd0/0xfc [kvm] > [c000000078d83cd0] [c0000000001be750] .compat_sys_ioctl+0x160/0x1864 > [c000000078d83e30] [c00000000000988c] syscall_exit+0x0/0x40 Hmm, unless smp_send_reschedule must be called with preemption disabled (doesn't seem like an obvious requirement, even if callers commonly have a reason to do so, and the only documentation of it I see is on the ia64 implementation), that seems like a bug in the MPIC IPI implementation. It wouldn't be an issue (and would make the MPIC driver slightly faster, too) if the MPIC driver were to use the magic CPU region instead of manually indexing the non-magic array of per-CPU regions. Maybe it doesn't work on all hardware the driver supports? Not that it matters much here -- we want this patch anyway, because we want to check that it's not the current CPU. -Scott -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
