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Message-ID: <CAJD7tkb7=sBdxXTmcqxe3+UWsTT7R6-rKGBhkEfgEAdTY+5jCw@mail.gmail.com>
Date: Tue, 2 Jul 2024 10:39:03 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v3 0/3] x86/mm: LAM fixups and cleanups
On Tue, Jul 2, 2024 at 10:36 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 2 Jul 2024 13:21:36 +0000 Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> > This series has fixups and cleanups for LAM. Most importantly, patch 1
> > fixes a sycnhronization issue that may cause crashes of userspace
> > applications. This is a resend of v3, rebased on top of v6.10-rc6.
>
> "Crashes of userspace applications" is bad. Yet the patchset has been
> floating about for four months.
>
> It's unclear (to me) how serious this is. Can you please explain how
> common this is, what the userspace application needs to do to trigger
> this, etc?
I don't think it would be common. The bug only happens on new hardware
supporting LAM, and it happens in a specific scenario where a
userspace task enables LAM while a kthread is using (borrowing) its
mm_struct on another CPU.
So it is possible but I certainly wouldn't call it common or easily triggerable.
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