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I've come across an interesting problem when testing my SMP support in VMware. In both my BSP and AP bootup code, I clear EFLAGS by doing the following: This works fine in both cases in QEMU, and on 2 real machines. In VMware, however, it works fine in the BSP case, but not on the AP, instead it causes a triple fault on the POPF. Even this faults: Unfortunately I can't see exactly what exception it's causing, but am I missing something obvious here? I have a stack set up correctly and a GDT, and all segment registers are set correctly. Anyone know what could be causing this?

Eeek, I feel such an idiot now! Minutes after I posted this I realised that I'd allocated the AP's stack using the kernel heap, and then attempted to convert the allocated address to a physical address as if it were an address in the physical map area. That's what I get for coding while tired

The scary part is that the code worked fine in Qemu and on two real machines with that bug in it... weird.

I assume it was because the address I was ending up with was free physical memory, whereas VMware was probably using it for special purposes (i.e. it wasn't usable memory, and instead some memory-mapped I/O or something).