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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id j7si2132032pgh.158.2019.07.12.05.51.05 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 12 Jul 2019 05:51:06 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=M2dP09VM; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=rwpolTjZGqbTjwkLH0mAAIVI9rPZBe7E59f4u4dvndk=; b=M2dP09VMp056HkHzjt4KD8h0P pj6x6MKN2KDyASTibms8pAubzJ1mr3Q41T5d9AbtwAdaZ7h5k8x3fIJL+eT7wXHVf4JC6fk9HXPkd Dl+vY4CxPI7HGeG5FRxCOoZOf+vS0SugPI9EnN3u5EEH+KgIrWyeM9oITXrkmbUl2JrcbiL8X0hip zWBcCskL2lMgRkYMZhT0e0cE6dgndhjznxtrzxudGf5lkhjjHKJGRS2R9TnhQ7woa9LpARKBL13k+ 6O5AuHeVjb4+jADAERfPyUCDygpN1T1I9gL6OaxZnhW7VPjq1virgpae/SjTED2hovlyYB1GQPs3X GHeANTbMQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hlv0v-0000Mt-GX; Fri, 12 Jul 2019 12:51:01 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BC3D4209772EE; Fri, 12 Jul 2019 14:50:59 +0200 (CEST) Date: Fri, 12 Jul 2019 14:50:59 +0200 From: Peter Zijlstra To: Alexandre Chartre Cc: Thomas Gleixner , Dave Hansen , pbonzini@redhat.com, rkrcmar@redhat.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, kvm@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, konrad.wilk@oracle.com, jan.setjeeilers@oracle.com, liran.alon@oracle.com, jwadams@google.com, graf@amazon.de, rppt@linux.vnet.ibm.com, Paul Turner Subject: Re: [RFC v2 00/27] Kernel Address Space Isolation Message-ID: <20190712125059.GP3419@hirez.programming.kicks-ass.net> References: <1562855138-19507-1-git-send-email-alexandre.chartre@oracle.com> <5cab2a0e-1034-8748-fcbe-a17cf4fa2cd4@intel.com> <61d5851e-a8bf-e25c-e673-b71c8b83042c@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <61d5851e-a8bf-e25c-e673-b71c8b83042c@oracle.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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, Jul 12, 2019 at 01:56:44PM +0200, Alexandre Chartre wrote: > I think that's precisely what makes ASI and PTI different and independent. > PTI is just about switching between userland and kernel page-tables, while > ASI is about switching page-table inside the kernel. You can have ASI without > having PTI. You can also use ASI for kernel threads so for code that won't > be triggered from userland and so which won't involve PTI. PTI is not mapping kernel space to avoid speculation crap (meltdown). ASI is not mapping part of kernel space to avoid (different) speculation crap (MDS). See how very similar they are? Furthermore, to recover SMT for userspace (under MDS) we not only need core-scheduling but core-scheduling per address space. And ASI was specifically designed to help mitigate the trainwreck just described. By explicitly exposing (hopefully harmless) part of the kernel to MDS, we reduce the part that needs core-scheduling and thus reduce the rate the SMT siblngs need to sync up/schedule. But looking at it that way, it makes no sense to retain 3 address spaces, namely: user / kernel exposed / kernel private. Specifically, it makes no sense to expose part of the kernel through MDS but not through Meltdow. Therefore we can merge the user and kernel exposed address spaces. And then we've fully replaced PTI. So no, they're not orthogonal.