linux-kernel - Re: [PATCH 01/26] mm: asi: Make some utility functions noinstr compatible

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Message-ID: <d0a38982-b811-4429-8b89-81e5da3aaf72@google.com>
Date: Thu, 31 Oct 2024 18:44:46 -0700
From: Junaid Shahid <junaids@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>,
 Brendan Jackman <jackmanb@...gle.com>, Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...hat.com>, Dave Hansen
 <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>, Alexandre Chartre <alexandre.chartre@...cle.com>,
 Liran Alon <liran.alon@...cle.com>,
 Jan Setje-Eilers <jan.setjeeilers@...cle.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>,
 Lorenzo Stoakes <lstoakes@...il.com>, David Hildenbrand <david@...hat.com>,
 Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
 Khalid Aziz <khalid.aziz@...cle.com>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Valentin Schneider <vschneid@...hat.com>, Paul Turner <pjt@...gle.com>,
 Reiji Watanabe <reijiw@...gle.com>, Ofir Weisse <oweisse@...gle.com>,
 Yosry Ahmed <yosryahmed@...gle.com>, Patrick Bellasi <derkling@...gle.com>,
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 Matteo Rizzo <matteorizzo@...gle.com>, Jann Horn <jannh@...gle.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 kvm@...r.kernel.org
Subject: Re: [PATCH 01/26] mm: asi: Make some utility functions noinstr
 compatible

On 10/29/24 12:12 PM, Thomas Gleixner wrote:
> 
> I doubt that it works as you want it to work.
> 
> +	inline notrace __attribute((__section__(".noinstr.text")))	\
> 
> So this explicitely puts the inline into the .noinstr.text section,
> which means when it is used in .text the compiler will generate an out-of
> line function in the .noinstr.text section and insert a call into the
> usage site. That's independent of the size of the inline.
> 

Oh, that's interesting. IIRC I had seen regular (.text) inline functions get 
inlined into .noinstr.text callers. I assume the difference is that here the 
section is marked explicitly rather than being implicit?

In any case, I guess we could just mark these functions as plain noinstr. 
(Unless there happens to be some other way to indicate to the compiler to place 
any non-inlined copy of the function in .noinstr.text but still allow inlining 
into .text if it makes sense optimization-wise.)

Thanks,
Junaid