Messages in this thread | | | Subject | Re: [PATCH 03/15] x86: remove early_gdt_descr reference | From | James Bottomley <> | Date | Mon, 09 Jun 2008 12:20:41 -0500 |
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On Mon, 2008-06-09 at 12:49 -0300, Glauber Costa wrote: > James Bottomley wrote: > > On Mon, 2008-06-09 at 11:16 -0300, Glauber Costa wrote: > >> since we use switch_to_new_gdt, there is no point > >> in assigning early_gdt_descr except for the first > >> assignment, which is done manually. > > > > What makes you think you can do this? If you don't update the early > > boot gdt, they all end up using the Boot CPU one. The problem with this > > is that there's a time from start_secondary to switch_to_new_gdt where > > the per cpu selector (%fs) and the pda selector (%gs) are those of the > > boot CPU. The former isn't a problem but the CPU number is in the > > latter, and it's used in that path before we get to the initialisation. > > You are right, I missed it. > > However, it only seem to be used in cpu_init, and very early. Sure there > are some users _before_ we load the new gdt, but nothing prevents them > to be moved after it. (Of course, this patch is wrong anyway). > > And if we do that, we can even take the %fs loading out of head_32.S > Of course, it's only valid if those are indeed the only early users of it. > > Is there any other use I'm missing?
Well, %fs loading there is done for the boot CPU. To eliminate that you have to not only verify that start_secondary doesn't use anything in per_cpu areas, but also verify that nothing in start_kernel() up until boot_cpu_init() does ... That's a lot of smp_processor_id() references to convert.
James
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