Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Feedback-ID: ie3994620:Fastmail
Date:   Wed, 11 Jan 2023 17:14:59 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Kostya Serebryany <kcc@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Taras Madan <tarasmadan@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        "H . J . Lu" <hjl.tools@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Bharata B Rao <bharata@amd.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>, Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCHv14 04/17] x86/mm: Handle LAM on context switch
Message-ID: <20230111141459.ah7ijfbm733c4g7m@box.shutemov.name>
References: <20230111123736.20025-1-kirill.shutemov@linux.intel.com>
 <20230111123736.20025-5-kirill.shutemov@linux.intel.com>
 <CAHk-=whb1_6qwb=BSpj1KkTfJiTiahAnvTBh_=fnGyrnKAW19A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHk-=whb1_6qwb=BSpj1KkTfJiTiahAnvTBh_=fnGyrnKAW19A@mail.gmail.com>
Precedence: bulk

On Wed, Jan 11, 2023 at 07:49:30AM -0600, Linus Torvalds wrote:
> 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?

It should be safe, yes. 

It is reachable from iommu_sva_bind_device(), but it only called with mm
== current->mm.

I will drop the READ_ONCE().

-- 
  Kiryl Shutsemau / Kirill A. Shutemov