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SubjectRe: x86_64: tss_struct layout does not match comments !?

* Richard Kennedy <richard@rsk.demon.co.uk> wrote:

> Hi Ingo,
>
> the comments in the definition of tss_struct suggests is should be
> cacheline aligned ( or 256 byte aligned ? ) :-
>
> |struct tss_struct {
> |....
> | /*
> | * Pad the TSS to be cacheline-aligned (size is 0x100):
> | */
> | unsigned long __cacheline_filler[35];
> | /*
> | * .. and then another 0x100 bytes for the emergency kernel stack:
> | */
> | unsigned long stack[64];
> |
> |} __attribute__((packed));
>
> However on a 64 bit build the size of tss_struct is 9136,
> cacheline_filler is 280 and stack size is 512 at offset 8624.
> None of which are cacheline aligned.
>
> I'm guessing this isn't what was intended.
>
> do you know what the original intention was ?
>
> 1. struct tss_struct{...} __cacheline_aligned;
> or just
> 2. struct tss_struct {
> ...
> long stack[64] __cacheline_aligned;
> }

#1 is the intent - because each CPU has a separate TSS. init_tss.stack
is really just an emergency static stack we have in place for very early
exceptions.

i think the __cacheline_filler could be removed safely. Mind sending a
patch for that?

Ingo


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