Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [Fastboot] [PATCH][RFC] x86_64: Reload CS when startup_64 is used. | Date | Mon, 21 Aug 2006 16:16:50 +0200 |
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On Monday 21 August 2006 15:29, Magnus Damm wrote: > On 8/21/06, Andi Kleen <ak@suse.de> wrote: > > > > > > > > + /* Reload CS with a value that is within our GDT. We need to do this > > > + * if we were loaded by a 64 bit bootloader that happened to use a > > > + * CS that is larger than the GDT limit. This is true if we came here > > > + * from kexec running under Xen. > > > + */ > > > + movq %rsp, %rdx > > > + movq $__KERNEL_DS, %rax > > > + pushq %rax /* SS */ > > > + pushq %rdx /* RSP */ > > > + movq $__KERNEL_CS, %rax > > > + movq $cs_reloaded, %rdx > > > + pushq %rax /* CS */ > > > + pushq %rdx /* RIP */ > > > + lretq > > > > Can't you just use a normal far jump? That might be simpler. > > I couldn't find a far jump that took a 64-bit address to jump to. But > I guess that the kernel will be loaded in the lowest 4G regardless so > I guess 32-bit pointers are ok, right? That will make it simpler for > sure.
Yes, that code always runs in the identity mapping and at 2MB.
> > What do you think about reloading CS? Is it the right thing to do, or > is it correct as it is today where we depend on that CS == _KERNEL_CS? > I need to fix kexec-tools regardless, but maybe it is a good idea to > make the 64-bit kernel boot a bit robust too.
Reloading CS is ok, although longer term I plan to switch the kernel to uncompress already in 64bit. Then you would need the same GDT anyways.
-Andi
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