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Shutemov" To: Michal Hocko Cc: Dave Hansen , Andy Lutomirski , Peter Zijlstra , x86@kernel.org, Kostya Serebryany , Andrey Ryabinin , Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR Message-ID: <20220616170510.gpm5pjd4yzk7hfsx@black.fi.intel.com> References: <20220610143527.22974-1-kirill.shutemov@linux.intel.com> <20220610143527.22974-7-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655399114; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=auHSjmEf/AyDtuDW/btQaQGbpEAuGl6dVEQEjFmcH58=; b=PO2tKJJtLvVNGgUDDj87elvwlTsg96TXy0JzEZ+Np58Z/mk/wsAVjEXJORsvkPaKWa7FvN BNWpgo5r5OtY7q9JocRN36MmoGrVWmLEHEf+P7WPk0b1y8e3d5i7OuPykPnmLWTqFttKC3 nUVKlj1CZ8X95FC5XCR21pYZUW2DLrk= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=lnj5v3jV; spf=none (imf11.hostedemail.com: domain of kirill.shutemov@linux.intel.com has no SPF policy when checking 134.134.136.65) smtp.mailfrom=kirill.shutemov@linux.intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655399114; a=rsa-sha256; cv=none; b=URZu6X/qLrQPWGrg2Q1hh/7qGb3NGjZwM3/E047OOU6BSgan7HN1YyakBXGcm1zvaWi296 RbjE2ziPgYJP7b0BgcHXoSWL/vES/hLxhjoiutRragnFUsp9xHzYz0ICpkOSMt8QioX/Qa 9aY3/P42Yex2eTKM7x5jGSPIOvCtRq4= X-Stat-Signature: tyzr8t5b9xiagq7uy8mbeaj4i4rrwycs X-Rspamd-Queue-Id: E89994008F X-Rspamd-Server: rspam11 X-Rspam-User: Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=lnj5v3jV; spf=none (imf11.hostedemail.com: domain of kirill.shutemov@linux.intel.com has no SPF policy when checking 134.134.136.65) smtp.mailfrom=kirill.shutemov@linux.intel.com; dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1655399113-82290 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: On Mon, Jun 13, 2022 at 04:42:57PM +0200, Michal Hocko wrote: > On Fri 10-06-22 17:35:25, Kirill A. Shutemov wrote: > [...] > > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c > > index 1962008fe743..93c8eba1a66d 100644 > > --- a/arch/x86/kernel/process_64.c > > +++ b/arch/x86/kernel/process_64.c > > @@ -742,6 +742,32 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr) > > } > > #endif > > > > +static int prctl_enable_tagged_addr(unsigned long nr_bits) > > +{ > > + struct mm_struct *mm = current->mm; > > + > > + /* Already enabled? */ > > + if (mm->context.lam_cr3_mask) > > + return -EBUSY; > > + > > + /* LAM has to be enabled before spawning threads */ > > + if (get_nr_threads(current) > 1) > > + return -EBUSY; > > This will not be sufficient in general. You can have mm shared with a > process without CLONE_THREAD. So you would also need to check also > MMF_MULTIPROCESS. But I do remember that general get_nr_threads is quite > tricky to use properly. Make sure to CC Oleg Nesterov for more details. > > Also how does this work when the mm is shared with a kernel thread? It seems we need to check mm_count to exclude kernel threads that use the mm. But I expect it to produce bunch of false-positives. Or we can make all CPUs to do switch_mm(current->mm, current->mm, current); and get LAM bits updated regardless what mm it runs. It would also remove limitation that LAM can only be enabled when there's no threads. But I feel that is a bad idea, but I have no clue why. :P -- Kirill A. Shutemov