Linux Virtualization - Oct 2023 - [PATCH v3 1/5] x86/paravirt: move some functions and defines to alternative

On 25.10.23 12:34, Borislav Petkov wrote:
> On Thu, Oct 19, 2023 at 11:15:16AM +0200, Juergen Gross wrote:
>> +/* Low-level backend functions usable from alternative code
replacements. */
>> +DEFINE_ASM_FUNC(x86_nop, "", .entry.text);
>> +EXPORT_SYMBOL_GPL(x86_nop);
> 
> This is all x86 code so you don't really need the "x86_"
prefix - "nop"
> is perfectly fine.
There is

#define nop() asm volatile ("nop")

in arch/x86/include/asm/special_insns.h already.
> 
>> +noinstr void x86_BUG(void)
>> +{
>> +	BUG();
>> +}
>> +EXPORT_SYMBOL_GPL(x86_BUG);
> 
> That export is needed for?
> 
> Paravirt stuff in modules?
> 
> It builds here without it - I guess I need to do an allmodconfig.
> 
It might not be needed now, but are you sure we won't need it in future?


Juergen
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On Wed, Oct 25, 2023 at 03:31:07PM +0200, Juergen Gross
wrote:
> There is
> 
> #define nop() asm volatile ("nop")
> 
> in arch/x86/include/asm/special_insns.h already.
Then call it "nop_func" or so.
> It might not be needed now, but are you sure we won't need it in
future?
No, I'm not.

What I'm sure of is: stuff should be added to the kernel only when
really needed. Not in the expectation that it might potentially be
needed at some point.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette