* Bart Kuivenhoven <bemk@xxxxxxxxxx> wrote: > On Fri, 2013-09-20 at 16:28 +0100, Matt Fleming wrote: > > On Wed, 18 Sep, at 07:28:53PM, Bart Kuivenhoven wrote: > > > The problem in efi_main was that the idt was cleared before the > > > interrupts were disabled. > > > > > > The UEFI spec states that interrupts aren't used so this shouldn't be > > > too much of a problem. Peripherals however don't necessarily know about > > > this and thus might cause interrupts to happen anyway. Even if > > > ExitBootServices() has been called. > > > > > > This means there is a risk of an interrupt being triggered while the IDT > > > register is nullified and the interrupt bit hasn't been cleared, > > > allowing for a triple fault. > > > > Just to be clear, you haven't witnessed a triple fault, correct? > > > > > This patch fixes this by clearing the interrupt bit before the lidt > > > instruction. > > > > I think we can go even further than this and get rid of all of the IDT > > code in the EFI boot stub. The kernel maintains its own IDT anyway. > > > > Well, isn't it so, that the kernel expects a setup in which interrupts > are disabled before the decompressed image is loaded? > > What we can do is remove the lidt instruction and IDT pointer, but that > still doesn't change anything with regards to the kernels expectations. > > And no, I haven't witnessed a triple fault, this is purely theoretical, > with a very slim chance of it actually happening. That does not mean > that it can't happen though. it would also be very hard to prove that it occured (outside of special debug environments) - spurious, low probability triple faults are as undebuggable as it gets. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
