linux-kernel - Re: [PATCH v11 05/12] x86/mm: add INVLPGB support code

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Message-ID: <cb55a019-50f1-4824-9a9f-9431d8b89ed7@intel.com>
Date: Wed, 19 Feb 2025 11:01:17 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Rik van Riel <riel@...riel.com>, Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, peterz@...radead.org,
 dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
 nadav.amit@...il.com, thomas.lendacky@....com, kernel-team@...a.com,
 linux-mm@...ck.org, akpm@...ux-foundation.org, jackmanb@...gle.com,
 jannh@...gle.com, mhklinux@...look.com, andrew.cooper3@...rix.com,
 Manali Shukla <Manali.Shukla@....com>
Subject: Re: [PATCH v11 05/12] x86/mm: add INVLPGB support code

On 2/19/25 09:42, Rik van Riel wrote:
> On Wed, 2025-02-19 at 13:04 +0100, Borislav Petkov wrote:
>> On Thu, Feb 13, 2025 at 11:13:56AM -0500, Rik van Riel wrote:
>>>
>>> index 000000000000..a1d5dedd5217
>>> --- /dev/null
>>> +++ b/arch/x86/include/asm/invlpgb.h
>>
>> I remember asking you to add all that gunk to
>> arch/x86/include/asm/tlb.h.
>> Please do so.
> 
> Dave just asked me to split out more things into
> their own files.
> 
> I'm happy to do whatever the maintainers want,
> but when you both want the opposite from each
> other, I won't be able to make you both happy.
> 
> What should I be doing here?

I think you're referring to this:

> https://lore.kernel.org/all/b067a9fc-ff5f-4baa-a1ff-3fa749ae4d44@intel.com/

I don't have a strong preference about creating an invlpgb.h header. As
long as the header is still relatively small the #ifdef pile is
readable, it's fine to stick in an existing header.

The thing I raised about the 09/12 patch was a large #ifdef in a .c
file. We have a general rule to avoid #ifdefs in .c files. Specifically,
I find that having large #ifdef's regions in a .c file means that you
literally can't see both sides of the #ifdef at once or easily
understand which code belongs to the #ifdef. The result is invariably
weird compile issues that pop up.

But, either way, #ifdefs are a sign of weakness. Less so in a header and
more so in a .c file.