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20 Aug 2018 16:27:19 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,267,1531810800"; d="scan'208";a="76960380" Received: from davehex.jf.intel.com (HELO [172.16.44.168]) ([10.7.198.90]) by orsmga003.jf.intel.com with ESMTP; 20 Aug 2018 16:26:59 -0700 Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU) To: David Woodhouse , Tycho Andersen , Linus Torvalds References: <20180820212556.GC2230@char.us.oracle.com> <1534801939.10027.24.camel@amazon.co.uk> <20180820223557.GC16961@cisco.cisco.com> <1534806880.10027.29.camel@infradead.org> Cc: Konrad Rzeszutek Wilk , juerg.haefliger@hpe.com, deepa.srinivasan@oracle.com, Jim Mattson , Andrew Cooper , Linux Kernel Mailing List , Boris Ostrovsky , linux-mm , Thomas Gleixner , joao.m.martins@oracle.com, pradeep.vincent@oracle.com, Andi Kleen , Khalid Aziz , kanth.ghatraju@oracle.com, Liran Alon , Kees Cook , jsteckli@os.inf.tu-dresden.de, Kernel Hardening , chris.hyser@oracle.com, Tyler Hicks , John Haxby , Jon Masters From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1534806880.10027.29.camel@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/20/2018 04:14 PM, David Woodhouse wrote: > If you need the physmap, then rather than manually mapping with 4KiB > pages, you just switch. Having first ensured that no malicious guest or > userspace is running on a sibling, of course. The problem is determining when "you need the physmap". Tycho's patches, as I remember them basically classify pages between being "user" pages which are accessed only via kmap() and friends and "kernel" pages which need to be mapped all the time because they might have a 'task_struct' or a page table or a 'struct file'. You're right that we could have a full physmap that we switch to for kmap()-like access to user pages. But, the real problem is transitioning pages from kernel to user usage since it requires shooting down the old kernel mappings for those pages in some way.