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Re: [Xen-devel] [PATCH 1/2] xen/link: Introduce .bss.percpu.page_aligned
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 26 Jul 2019 15:30:35 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Fri, 26 Jul 2019 14:30:46 +0000
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On 26/07/2019 15:22, Roger Pau Monné wrote:
> On Fri, Jul 26, 2019 at 02:52:39PM +0100, Andrew Cooper wrote:
>> Future changes are going to need to page align some percpu data.
>>
>> This means that the percpu area needs suiably aligning in the BSS so CPU0 has
>> correctly aligned data. Shuffle the exact link order of items within the BSS
>> to give .bss.percpu.page_aligned appropriate alignment.
>>
>> Additionally, introduce DEFINE_PER_CPU_PAGE_ALIGNED()
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Wei Liu <wl@xxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>> CC: Julien Grall <julien.grall@xxxxxxx>
>> CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
>> ---
>> xen/arch/arm/xen.lds.S | 5 +++--
>> xen/arch/x86/xen.lds.S | 5 +++--
>> xen/include/xen/percpu.h | 2 ++
>> 3 files changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
>> index 12c107f45d..07cbdf2543 100644
>> --- a/xen/arch/arm/xen.lds.S
>> +++ b/xen/arch/arm/xen.lds.S
>> @@ -201,14 +201,15 @@ SECTIONS
>> *(.bss.stack_aligned)
>> . = ALIGN(PAGE_SIZE);
>> *(.bss.page_aligned)
>> - *(.bss)
>> - . = ALIGN(SMP_CACHE_BYTES);
> Don't you also need a:
>
> . = ALIGN(PAGE_SIZE);
>
> here?
No, (I don't think so).
> Or is the size of .bss.page_aligned also aligned to page size?
Every object inside .bss.page_aligned should have suitable (i.e.
multiple of) size and alignment. Without this, things will break.
~Andrew
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