[SeaBIOS] [RFC PATCH v3 0/3] Add segment limit checks to emulator
kevin at koconnor.net
Sun Jul 25 19:19:58 CEST 2010
On Sun, Jul 25, 2010 at 12:42:46PM -0400, Kevin O'Connor wrote:
> On Sun, Jul 25, 2010 at 11:55:47AM +0300, Avi Kivity wrote:
> > What conditions are needed to trigger this path? This can't occur
> > under normal operation, since it will fail badly with kvm on Intel.
> It's called on every boot. I've personally only tested kvm on amd,
> but I'd have to assume something must be allowing this to work on
BTW, the transition16big code does:
ljmpl $SEG32_MODE16BIG_CS, $(0xf0000 + 1f)
// Disable protected mode
movl %cr0, %eax
andl $~CR0_PE, %eax
movl %eax, %cr0
// far jump to flush CPU queue after transition to real mode
ljmpw $0xf000, $2f
Only the ljmpw is in big real mode with a code address >64K - the
"Disable protected mode" code is technically in 16bit protected mode.
I'm not sure if that helps explain why it works.
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