linux-kernel - Re: [RFC PATCH 1/3] x86/mm: fix LAM cr3 mask inconsistency during context switch

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Message-ID: <CAJD7tkaRV4APEYECL_rThr5ArWaLpUG+eBiwgxqe49N6sMRBbg@mail.gmail.com>
Date: Thu, 7 Mar 2024 15:37:04 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>, 
	Andy Lutomirski <luto@...nel.org>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, x86@...nel.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] x86/mm: fix LAM cr3 mask inconsistency during
 context switch

> > Or we can avoid returning a value from the helper and avoid passing an
> > mm. The callers would be more verbose, they'll have to call
> > mm_lam_cr3_mask() and mm_untag_mask() and pass the results into the
> > helper (set_tlbstate_lam_mode() or update_cpu_tlbstate_lam()). Another
> > advantage of this is that we can move the READ_ONCE to
> > switch_mm_irqs_off() and keep the comment here.
>
>
> One thing I don't like about set_tlbstate_lam_mode() is that it's not
> obvious that it's writing to "cpu_tlbstate" and its right smack in the
> middle of a bunch of other writers to the same thing.
>
> But I'm also not sure that open-coding it at its three call sites makes
> things better overall.
>
> I honestly don't have any brilliant suggestions.

Let me ponder this a little bit and try to come up with something, I
think a max of renaming and open-coding could make an improvement.

Thanks!