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Shutemov" 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: 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: <20220610143527.22974-7-kirill.shutemov@linux.intel.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655131380; a=rsa-sha256; cv=none; b=gJUMhyGJisHSKa7C0GazMsGT+rhfaEzI768meOc3R3qlve+aUvmwiqSrAdEsgRcuRaog5K SQqlYG4wIOeozxdj82gi6l5Bmkl5HOmpC1Uv25pUbnJ9eqA1Y9/hszJP7n6a7G/bh7ZTYX Pa54yHfGWKx/0zBXFv/kXXHihkwupXc= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=VlIj+b5w; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf02.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655131380; 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=0UHKdjPy6Bns5JU9HOJ8DtOlOS3bAJA+b5m8rgKgBio=; b=qC0BOLofuPAb3uiHbLBkoVE2MKUfdhep5/QCYN9IT7nCakDRyIuP2PqRKmGX466M92ZFal qnTGAtYhRGq6ZnRKeUjX/WQBE4iMMASTqUgpLiJbGeXDKHC2AaVJX8UgiGlwnKmOq++8z2 PjIr+sssgrVj0CarAScB1/L7rBMTVl0= Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=VlIj+b5w; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf02.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspam-User: X-Rspamd-Server: rspam01 X-Stat-Signature: 74piu8hkx89a9oaemp1zat6p59dteba4 X-Rspamd-Queue-Id: CFA9880223 X-HE-Tag: 1655131379-720247 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 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? > + > + if (!nr_bits) { > + return -EINVAL; > + } else if (nr_bits <= 6) { > + mm->context.lam_cr3_mask = X86_CR3_LAM_U57; > + mm->context.untag_mask = ~GENMASK(62, 57); > + } else { > + return -EINVAL; > + } > + > + /* Update CR3 to get LAM active */ > + switch_mm(current->mm, current->mm, current); > + return 0; > +} -- Michal Hocko SUSE Labs