Re: [PATCH 07/16] x86/asm: Move SYSENTER_stack to the beginning of struct tss_struct

[Andy Lutomirski]

On Mon, Nov 20, 2017 at 3:37 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Mon, 20 Nov 2017, Andy Lutomirski wrote:
>>  struct tss_struct {
>>       /*
>> -      * The hardware state:
>> +      * Space for the temporary SYSENTER stack.  Used for the entry
>> +      * trampoline as well.  Size it such that tss_struct ends up
>> +      * as a multiple of PAGE_SIZE.  This calculation assumes that
>> +      * io_bitmap is a multiple of PAGE_SIZE (8192 bytes) plus one
>> +      * long.
>
> I don't see how sizeof(tss_struct) is a multiple of PAGE_SIZE
>
> canary          =    8
> stack           =  512
> hw_tss          =  104
> io bitmap       = 8200
> -------------------------
>                   8824
>
> The alignment is what blows it up to 3 * PAGE_SIZE

Whoops!  That *was* correct in the RFC version version, but I changed
it and failed to fix the comment.