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AJvYcCWbHjzxKWnSy/igB/ywb47FEmy4wM4AN1Jt2Ve5OCJzpXMI0p50MZjlt8HR+aWr1L3itOMbIYad121S+5t8i4+Hf58= X-Gm-Message-State: AOJu0Yz8zdWvRaFSXUbc9uH7TRCuTXi00dOEUELwFRZ7bYBS1qs4UgcP o75pOH+iFhsTWd8ewMVsyTu/DQmQIXIrrxcS+UC3viWV5/qTSHdEnmYohPhcR+eFiDDiyNQDX77 aKxUuJVkarhn3xYx7NwKH7OQHYFz3R7FgqgEZ X-Google-Smtp-Source: AGHT+IHrLmjzFAJTYl5719GqKvfQGhtCq5ZY6aYr3tOzSCXcxH1gXnPhub/BsTtVRYnXofvsz0JrLVDlNZB9+mS3OBA= X-Received: by 2002:a19:641e:0:b0:513:4764:2fa5 with SMTP id y30-20020a19641e000000b0051347642fa5mr5008706lfb.41.1710181717177; Mon, 11 Mar 2024 11:28:37 -0700 (PDT) MIME-Version: 1.0 References: <20240307133916.3782068-1-yosryahmed@google.com> <20240307133916.3782068-3-yosryahmed@google.com> <420fcb06-c3c3-4e8f-a82d-be2fb2ef444d@app.fastmail.com> <35b670e2-9ef5-4d3a-b6ea-f8016dfa088d@intel.com> In-Reply-To: From: Yosry Ahmed Date: Mon, 11 Mar 2024 11:27:58 -0700 Message-ID: Subject: Re: [RFC PATCH 2/3] x86/mm: make sure LAM is up-to-date during context switching To: "Kirill A. Shutemov" Cc: Dave Hansen , Andy Lutomirski , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "Peter Zijlstra (Intel)" , "the arch/x86 maintainers" , linux-mm@kvack.org, Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 2555940018 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: b5dmh1oo1jznusum3nchm8tmpuqnyj4j X-HE-Tag: 1710181718-225153 X-HE-Meta: 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 2yQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 11, 2024 at 5:42=E2=80=AFAM Kirill A. Shutemov wrote: > > On Sat, Mar 09, 2024 at 01:37:06PM -0800, Yosry Ahmed wrote: > > On Sat, Mar 9, 2024 at 8:34=E2=80=AFAM Kirill A. Shutemov > > 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 n= eeds. > > > 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? > > You are right. I think IPI is the way to go. > > Will you prepare a patch? I am working on it.