From: Yosry Ahmed <yosryahmed@google.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
linux-mm@kvack.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 2/3] x86/mm: make sure LAM is up-to-date during context switching
Date: Sat, 9 Mar 2024 13:37:06 -0800 [thread overview]
Message-ID: <CAJD7tkZABvm4v87T2WJ593sjZ_Z9iLCcgecghQJHrZDnuisBLg@mail.gmail.com> (raw)
In-Reply-To: <o5t3qrrlw37hdkcja2vny3ycpmhb4dowmdj74a2wrq2x4xctqk@5g5jvzen46qe>
On Sat, Mar 9, 2024 at 8:34 AM Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> On Sat, Mar 09, 2024 at 02:19:19AM +0000, Yosry Ahmed wrote:
> > I don't see how skipping set_tlbstate_lam_mode() for kthreads fixes this
> > problem. Do you mind elaborating?
>
> Define what problem is.
>
> Yes, in this scenario kthread gets more permissive LAM mode than it needs.
> But nothing breaks.
The problem here is not how the kthread runs at all. It is the fact
that if that kthread context switches into the user process that has
enabled LAM, it may not update CR3 because the mm doesn't change.
switch_mm_irqs_off() will only update CR3 in this case if there is a
pending TLB flush. Otherwise, we just return, even if the LAM for this
mm has changed.
This can cause the process that has enabled LAM to run with LAM
disabled and fault on tagged addresses, right? Did I miss something?
next prev parent reply other threads:[~2024-03-09 21:37 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-07 13:39 [RFC PATCH 0/3] x86/mm: LAM fixups and cleanups Yosry Ahmed
2024-03-07 13:39 ` [RFC PATCH 1/3] x86/mm: fix LAM cr3 mask inconsistency during context switch Yosry Ahmed
2024-03-07 17:22 ` Kirill A. Shutemov
2024-03-07 20:31 ` Yosry Ahmed
2024-03-07 17:36 ` Dave Hansen
2024-03-07 18:49 ` Sean Christopherson
2024-03-07 20:44 ` Yosry Ahmed
2024-03-07 22:12 ` Sean Christopherson
2024-03-07 20:42 ` Yosry Ahmed
2024-03-07 23:21 ` Yosry Ahmed
2024-03-07 23:32 ` Dave Hansen
2024-03-07 23:37 ` Yosry Ahmed
2024-03-07 13:39 ` [RFC PATCH 2/3] x86/mm: make sure LAM is up-to-date during context switching Yosry Ahmed
2024-03-07 15:29 ` Dave Hansen
2024-03-07 21:04 ` Yosry Ahmed
2024-03-07 21:39 ` Dave Hansen
2024-03-07 22:29 ` Yosry Ahmed
2024-03-07 22:41 ` Dave Hansen
2024-03-07 22:44 ` Yosry Ahmed
2024-03-08 1:26 ` Yosry Ahmed
2024-03-08 8:09 ` Yosry Ahmed
2024-03-07 17:29 ` Kirill A. Shutemov
2024-03-07 17:56 ` Dave Hansen
2024-03-07 21:08 ` Yosry Ahmed
2024-03-07 21:48 ` Dave Hansen
2024-03-07 22:30 ` Yosry Ahmed
2024-03-08 1:34 ` Andy Lutomirski
2024-03-08 1:47 ` Yosry Ahmed
2024-03-08 14:05 ` Kirill A. Shutemov
2024-03-08 15:23 ` Dave Hansen
2024-03-08 18:18 ` Kirill A. Shutemov
2024-03-09 2:19 ` Yosry Ahmed
2024-03-09 16:34 ` Kirill A. Shutemov
2024-03-09 21:37 ` Yosry Ahmed [this message]
2024-03-11 12:42 ` Kirill A. Shutemov
2024-03-11 18:27 ` Yosry Ahmed
2024-03-07 13:39 ` [RFC PATCH 3/3] x86/mm: cleanup prctl_enable_tagged_addr() nr_bits error checking Yosry Ahmed
2024-03-07 17:31 ` Kirill A. Shutemov
2024-03-07 20:27 ` Yosry Ahmed
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