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[209.85.160.172]) by smtp.gmail.com with ESMTPSA id c11-20020ac853cb000000b00397b1c60780sm7509046qtq.61.2023.01.11.05.49.41 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Jan 2023 05:49:41 -0800 (PST) Received: by mail-qt1-f172.google.com with SMTP id fa5so8367473qtb.11 for ; Wed, 11 Jan 2023 05:49:41 -0800 (PST) X-Received: by 2002:ac8:4e26:0:b0:3a7:648d:23d4 with SMTP id d6-20020ac84e26000000b003a7648d23d4mr4849733qtw.180.1673444981001; Wed, 11 Jan 2023 05:49:41 -0800 (PST) MIME-Version: 1.0 References: <20230111123736.20025-1-kirill.shutemov@linux.intel.com> <20230111123736.20025-5-kirill.shutemov@linux.intel.com> In-Reply-To: <20230111123736.20025-5-kirill.shutemov@linux.intel.com> From: Linus Torvalds Date: Wed, 11 Jan 2023 07:49:30 -0600 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCHv14 04/17] x86/mm: Handle LAM on context switch To: "Kirill A. Shutemov" Cc: Dave Hansen , Andy Lutomirski , Peter Zijlstra , "the arch/x86 maintainers" , Kostya Serebryany , Andrey Ryabinin , Andrey Konovalov , Alexander Potapenko , Taras Madan , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , Bharata B Rao , Jacob Pan , Ashok Raj , Linux-MM , Linux Kernel Mailing List Content-Type: multipart/alternative; boundary="000000000000a4ee6e05f1fd45e9" X-Rspamd-Queue-Id: CE768160006 X-Stat-Signature: 5xwfmm7c6yir46iojf9omyctqbgm1s63 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1673444983-672035 X-HE-Meta: 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 eNCaZaBr S5AdgbatqbNJZabCrMSyP79ReCgibKuKr/KRud7Pjy2e+L6XQjo1Gx1gtIr+q0hxXiXdHY3gpWlsS2kFTQghw4nITR28+B2SA/49OhU8uzf4Nd1HdTpzvI4UU3Kxhu/8Xr1+8izgNgs2qmvHP88YoFwLxUzs2U1DpNxO8l+er8UvERSJlOCz4nucXevl6Xplkey77NOvZMgoD3BwcFzFUK5BusTY4wYVmrqTCFzjIubTu8sAvZvVkDcEjsKzi7uIfb15tr4kRQxqhrVg6/tTuTAQ3OEXM5+QMhUQ0Z2KXdBsWYpLLAurJFwfU6sS/yKAeu4LO5L8gdDWEAZuqhm6z2UNnFeUYk9XAXucmpDknfLFvHMmc/E084rbyEr7dv58vtLp5/E9EC/bbIwXsUkUs9C9IQg== 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: --000000000000a4ee6e05f1fd45e9 Content-Type: text/plain; charset="UTF-8" Sorry, I'm traveling, and right now only on mobile. So I'm reading patches on my phone, and answering on it too, so html garbage.. On Wed, Jan 11, 2023, 07:24 Kirill A. Shutemov < kirill.shutemov@linux.intel.com> wrote: > > +static inline unsigned long mm_lam_cr3_mask(struct mm_struct *mm) > +{ > + return READ_ONCE(mm->context.lam_cr3_mask); > +} > I mentioned this before - in the original version this needed (but didn't have, iirc) that READ_ONCE, but in the new non-thread situation I don't think that's true. There should be no concurrent changes that can interfere with the read, no? If there is a reason for that READ_ONCE still, please add a comment for it Linus > --000000000000a4ee6e05f1fd45e9 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Sorry, I'm traveling, and right now only on mobi= le. So I'm reading patches on my phone, and answering on it too, so htm= l garbage..

On Wed, Jan 11, 2023, 07:24 Kirill A. Shutemov <kirill.shutemov@linux.intel.com>= wrote:

+static inline unsigned long mm_lam_cr3_mask(struct mm_struct *mm)
+{
+=C2=A0 =C2=A0 =C2=A0 =C2=A0return READ_ONCE(mm->context.lam_cr3_mask);<= br> +}

I mentioned this before - in the original version this needed (but didn&#= 39;t have, iirc) that READ_ONCE, but in the new non-thread situation I don&= #39;t think that's true. There should be no concurrent changes that can= interfere with the read, no?

If there is a reason for that READ_ONCE still, please add a comment f= or it=C2=A0

=C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0Linus
--000000000000a4ee6e05f1fd45e9--