linux-kernel - Re: [PATCH RESEND v2] docs: x86: Remove obsolete information about x86

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Date:   Fri, 20 Aug 2021 11:14:52 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Joerg Roedel <jroedel@...e.de>, Peilin Ye <yepeilin.cs@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Muchun Song <songmuchun@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        Peilin Ye <peilin.ye@...edance.com>
Subject: Re: [PATCH RESEND v2] docs: x86: Remove obsolete information about
 x86_64 vmalloc() faulting

Joerg Roedel <jroedel@...e.de> writes:

> On Wed, Aug 18, 2021 at 03:01:23PM -0700, Peilin Ye wrote:
>> From: Peilin Ye <peilin.ye@...edance.com>
>> 
>> x86_64 vmalloc() mappings are no longer "synchronized" among page tables
>> via faulting since commit 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD
>> pages for vmalloc area"), since the corresponding P4D or PUD pages are
>> now preallocated at boot, by preallocate_vmalloc_pages().  Drop the
>> "lazily synchronized" description for less confusion.
>> 
>> While this file is x86_64-specific, it is worth noting that things are
>> different for x86_32, where vmalloc()-related changes to `init_mm.pgd` are
>> synchronized to all page tables in the system during runtime, via
>> arch_sync_kernel_mappings().  Unfortunately, this synchronization is
>> subject to race condition, which is further handled via faulting, see
>> vmalloc_fault().  See commit 4819e15f740e ("x86/mm/32: Bring back vmalloc
>> faulting on x86_32") for more details.
>> 
>> Reviewed-by: Muchun Song <songmuchun@...edance.com>
>> Signed-off-by: Peilin Ye <peilin.ye@...edance.com>
>
> Reviewed-by: Joerg Roedel <jroedel@...e.de>

Applied, thanks.

jon