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Re: [PATCH V3 (resend) 08/19] xen/x86: Add build assertion for fixmap entries
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Elias El Yandouzi <eliasely@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 14 May 2024 11:45:39 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, julien@xxxxxxx, pdurrant@xxxxxxxxxx, dwmw@xxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Tue, 14 May 2024 09:45:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.05.2024 11:42, Roger Pau Monné wrote:
> On Mon, May 13, 2024 at 01:40:35PM +0000, Elias El Yandouzi wrote:
>> The early fixed addresses must all fit into the static L1 table.
>> Introduce a build assertion to this end.
>>
>> Signed-off-by: Elias El Yandouzi <eliasely@xxxxxxxxxx>
>>
>> ----
>>
>> Changes in v2:
>> * New patch
>>
>> diff --git a/xen/arch/x86/include/asm/fixmap.h
>> b/xen/arch/x86/include/asm/fixmap.h
>> index a7ac365fc6..904bee0480 100644
>> --- a/xen/arch/x86/include/asm/fixmap.h
>> +++ b/xen/arch/x86/include/asm/fixmap.h
>> @@ -77,6 +77,11 @@ enum fixed_addresses {
>> #define FIXADDR_SIZE (__end_of_fixed_addresses << PAGE_SHIFT)
>> #define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
>>
>> +static inline void fixaddr_build_assertion(void)
>> +{
>> + BUILD_BUG_ON(FIX_PMAP_END > L1_PAGETABLE_ENTRIES - 1);
>> +}
>
> Just introduce the BUILD_BUG_ON somewhere else, no need for a new
> function just for this.
And especially not in an inline function (thus triggering the potential error
perhaps several dozen times in a highly parallel build).
> Adding the BUILD_BUG_ON() to pmap_map() would be perfectly fine.
Nevertheless we have build_assertions() functions in a couple of places, so
yes, there are precedents to doing so rather that putting the constructs at
more or less random places.
Jan
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