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Re: [Xen-devel] [PATCH v3 1/2] xen/link: Introduce .bss.percpu.page_aligned


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 30 Jul 2019 10:35:58 +0100
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  • Cc: StefanoStabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Tue, 30 Jul 2019 09:36:18 +0000
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On 30/07/2019 09:42, Jan Beulich wrote:
> On 29.07.2019 19:38, Andrew Cooper wrote:
>> --- a/xen/arch/x86/xen.lds.S
>> +++ b/xen/arch/x86/xen.lds.S
>> @@ -293,14 +293,17 @@ SECTIONS
>>         __bss_start = .;
>>         *(.bss.stack_aligned)
>>         *(.bss.page_aligned*)
>> -       *(.bss)
>> -       . = ALIGN(SMP_CACHE_BYTES);
>> +       . = ALIGN(PAGE_SIZE);
>>         __per_cpu_start = .;
>> +       *(.bss.percpu.page_aligned)
>> +       . = ALIGN(PAGE_SIZE);
> But this goes too far: What we want is for the TSS to occupy a full
> page, not for whatever random other page-aligned object ends up
> last here (should any every appear).

Come again?  This is ridiculous.

Objects in a section following foo.page_aligned should never end up in
the tail of the final page of foo.page_aligned, because then they are in
the wrong section.

A short TSS is a pain to deal with, but even you said you didn't like
the xen_tss idea when you suggested it.

The name of the section is very deliberately not TSS specific, because
there is plenty of other cleanup which will end up with objects in this
section.

~Andrew

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