linux-kernel - Re: [PATCH 01/12] x86/mm: make MMU_GATHER_RCU_TABLE

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Message-ID: <20241230184118.GMZ3LpTn3dHvu_bq-p@fat_crate.local>
Date: Mon, 30 Dec 2024 19:41:18 +0100
From: Borislav Petkov <bp@...en8.de>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	akpm@...ux-foundation.org, nadav.amit@...il.com,
	zhengqi.arch@...edance.com, linux-mm@...ck.org
Subject: Re: [PATCH 01/12] x86/mm: make MMU_GATHER_RCU_TABLE_FREE
 unconditional

On Mon, Dec 30, 2024 at 12:53:02PM -0500, Rik van Riel wrote:
> Currently x86 uses CONFIG_MMU_GATHER_TABLE_FREE when using
> paravirt, and not when running on bare metal.
> 
> There is no real good reason to do things differently for
> each setup. Make them all the same.
> 
> After this change, the synchronization between get_user_pages_fast
> and page table freeing is handled by RCU, which prevents page tables
> from being reused for other data while get_user_pages_fast is walking
> them.

I'd rather like to read here why this is not a problem anymore and why

  48a8b97cfd80 ("x86/mm: Only use tlb_remove_table() for paravirt")

is not relevant anymore.

> This allows us to invalidate page tables while other CPUs have
	      ^^

Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.

Personal pronouns are ambiguous in text, especially with so many
parties/companies/etc developing the kernel so let's avoid them please.

-- 
Regards/Gruss,
    Boris.

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