linux-kernel - Re: [PATCH v6 01/12] x86/mm: make MMU_GATHER_RCU_TABLE

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Message-ID: <378ab76e-6f31-4ef4-b4bc-7c78cc307875@redhat.com>
Date: Mon, 20 Jan 2025 20:32:57 +0100
From: David Hildenbrand <david@...hat.com>
To: Rik van Riel <riel@...riel.com>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, bp@...en8.de, 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, jannh@...gle.com,
 mhklinux@...look.com, andrew.cooper3@...rix.com
Subject: Re: [PATCH v6 01/12] x86/mm: make MMU_GATHER_RCU_TABLE_FREE
 unconditional

On 20.01.25 03:40, 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.
> 
> Currently get_user_pages_fast synchronizes against page table
> freeing in two different ways:
> - on bare metal, by blocking IRQs, which block TLB flush IPIs
> - on paravirt, with MMU_GATHER_RCU_TABLE_FREE

Right, worth noting the latter also right now relies on the blocking of 
IRQs that is in place, because they implicitly block the RCU sync.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb