linux-kernel - Re: [PATCH] Grab mm lock before grabbing pt lock

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Message-ID: <813d9908-48e4-46ce-87c9-7414170e6a6e@exostellar.io>
Date: Mon, 9 Dec 2024 13:39:30 +0100
From: Maksym Planeta <maksym@...stellar.io>
To: Dave Hansen <dave.hansen@...el.com>, Juergen Gross <jgross@...e.com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Grab mm lock before grabbing pt lock

On 05/12/2024 19:52, Dave Hansen wrote:
> I have the _feeling_ it's just a big hack and this code throws caution
> tot the wind because of:
> 
>>   * Expected to be called in stop_machine() ("equivalent to taking
>>   * every spinlock in the system"), so the locking doesn't really
>>   * matter all that much.
> 
> So the patch here kinda doubles down on the hack and continues the theme
> because "locking doesn't really matter all that much."
> 
> If so, it's not super satisfying, but it is consistent with the existing
> code.
> 

I indeed could not find reasons why locking would be strictly necessary for correctness here. On the other hand a 
clearly benign warning should not be triggered, especially considering that panic_on_warn may be on on some systems.