Re: EFI mixed mode + perf = rampant triple faults

[Matt Fleming <matt-HNK1S37rvNbeXh+fF434Mdi2O/JbrIOy@public.gmane.org>]

On Wed, 14 Jan, at 10:27:47AM, Andy Lutomirski wrote:
> 
> How are you manually triggering an MCE?  I've been playing with some
> MCE stuff recently, but the only reasonably reliable way I know of to
> trigger an MCE is using WHEA, and I don't have a box with WHEA, and I
> assume your ASUS T100 doesn't either.
 
As Borislav mentions, I used 'int $18', solely to trigger the 64-bit
exception handler code paths in the middle of the EFI mixed mode code.

> > Where this won't work so well is at boot time before we jump to the
> > kernel proper. There, we still need to restore the firmware's GDT so
> > that interrupts are serviced correctly before ExitBootServices() (in
> > particular, ia32 Tianocore assumes __KERNEL_CS is a 32-bit CS).
> 
> Tianocore makes assumptions about the kernel's GDT layout?  Yuck.

No, but 32-bit Tianocore does rely on the second GDT entry being a
32-bit CS.

It has no knowledge of Linux's GDT layout.

-- 
Matt Fleming, Intel Open Source Technology Center