There are currently two different versions of stop_this_cpu() used to
halt an AP CPU after init and microcode update.
Alternative #1, the default
stop_this_cpu()
{
while (1) { hlt() }
}
Alternative #2, used on selected Intel Cores
stop_this_cpu()
{
send INIT IPI message to self
/* should not reach here */
while (1) { hlt() }
}
I would like to know the reasoning for implementing #2. Was this a
solution to an observed problem? The commentary speaks about
hyper-threading, while the processor models with the AP_IN_SIPI_WAIT
enabled are really multi-core.
I believe alternative #1 one is not sufficient for any SMP platform. If
an exception raises and the AP CPU has NULL IDT, a hyper-threading CPU
may shutdown its sibling CPUs in the same physical package. If there is
a valid IDT and the exception handler returns, memory at CS:EIP may no
longer contain the hlt() loop.
Thanks,
KM
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