It turns out that a PV domU also requires the "Xen PV" APIC
driver. Otherwise, the flat driver is used and we get stuck in busy
loops that never exit, such as in this stack trace:
(gdb) target remote localhost:9999
Remote debugging using localhost:9999
__xapic_wait_icr_idle () at ./arch/x86/include/asm/ipi.h:56
56 while (native_apic_mem_read(APIC_ICR) & APIC_ICR_BUSY)
(gdb) bt
#0 __xapic_wait_icr_idle () at ./arch/x86/include/asm/ipi.h:56
#1 __default_send_IPI_shortcut (shortcut=<optimized out>,
dest=<optimized out>, vector=<optimized out>) at
./arch/x86/include/asm/ipi.h:75
#2 apic_send_IPI_self (vector=246) at arch/x86/kernel/apic/probe_64.c:54
#3 0xffffffff81011336 in arch_irq_work_raise () at
arch/x86/kernel/irq_work.c:47
#4 0xffffffff8114990c in irq_work_queue (work=0xffff88000fc0e400) at
kernel/irq_work.c:100
#5 0xffffffff8110c29d in wake_up_klogd () at kernel/printk/printk.c:2633
#6 0xffffffff8110ca60 in vprintk_emit (facility=0, level=<optimized
out>, dict=0x0 <irq_stack_union>, dictlen=<optimized out>,
fmt=<optimized out>, args=<optimized out>)
at kernel/printk/printk.c:1778
#7 0xffffffff816010c8 in printk (fmt=<optimized out>) at
kernel/printk/printk.c:1868
#8 0xffffffffc00013ea in ?? ()
#9 0x0000000000000000 in ?? ()
Mailing-list-thread: https://lkml.org/lkml/2015/8/4/755
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
fc5fee86bd