Re: [PATCH][RFC] x86_64: Reload CS when startup_64 is used.

[ebiederm@xmission.com (Eric W. Biederman)]

Magnus Damm <magnus@valinux.co.jp> writes:

> x86_64: Reload CS when startup_64 is used.
>
> The current x86_64 startup code never reloads CS during the early boot process
> if the 64-bit function startup_64 is used as entry point. The 32-bit entry 
> point startup_32 does the right thing and reloads CS, and this is what most 
> people are using if they use bzImage.
>
> This patch fixes the case when the Linux kernel is booted into using kexec
> under Xen. The Xen hypervisor is using large CS values which makes the x86_64
> kernel fail - but only if vmlinux is booted, bzImage works well because it
> is using the 32-bit entry point.
>
> The main question is if we require that the boot loader should setup CS
> to some certain offset to be able to boot the kernel. The sane solution IMO
> should be that the kernel requires that the loaded descriptors are correct, 
> but that the exact offset within the GDT the boot loader is using should not 
> matter. This is the way the i386 boot works if I understand things correctly.

What extra reload of cs does Xen introduce?

I'm not really comfortable with a half virtualized case.

Eric