From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933301AbdKAU7T (ORCPT ); Wed, 1 Nov 2017 16:59:19 -0400 Received: from mga02.intel.com ([134.134.136.20]:1204 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933124AbdKAU7S (ORCPT ); Wed, 1 Nov 2017 16:59:18 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,330,1505804400"; d="scan'208";a="144812722" Subject: Re: [PATCH 21/23] x86, pcid, kaiser: allow flushing for future ASID switches To: Andy Lutomirski References: <20171031223146.6B47C861@viggo.jf.intel.com> <20171031223224.B9F5D5CA@viggo.jf.intel.com> <38b34f81-3adb-98c5-c482-0d53b9155d3b@linux.intel.com> Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , moritz.lipp@iaik.tugraz.at, Daniel Gruss , michael.schwarz@iaik.tugraz.at, Linus Torvalds , Kees Cook , Hugh Dickins , X86 ML From: Dave Hansen Message-ID: <5bc39561-b65e-82fd-3218-d91a4d22613a@linux.intel.com> Date: Wed, 1 Nov 2017 13:59:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/01/2017 01:31 PM, Andy Lutomirski wrote: > On Wed, Nov 1, 2017 at 7:17 AM, Dave Hansen wrote: >> On 11/01/2017 01:03 AM, Andy Lutomirski wrote: >>>> This ensures that any futuee context switches will do a full flush >>>> of the TLB so they pick up the changes. >>> I'm convuced. What was wrong with the old code? I guess I just don't >>> see what the problem is that is solved by this patch. >> >> Instead of flushing *now* with INVPCID, this lets us flush *later* with >> CR3. It just hijacks the code that you already have that flushes CR3 >> when loading a new ASID by making all ASIDs look new in the future. >> >> We have to load CR3 anyway, so we might as well just do this flush then. > > Would it make more sense to put it in flush_tlb_func_common() instead? > > Also, I don't understand what clear_non_loaded_ctxs() is trying to do. > It looks like it's invalidating all the other logical address spaces. > And I don't see why you want a all_other_ctxs_invalid variable. Isn't > the goal to mark a single ASID as needing a *user* flush the next time > we switch to user mode using that ASID? Your code seems like it's > going to flush a lot of *kernel* PCIDs. The point of the whole thing is to (relatively) efficiently flush *kernel* TLB entries in *other* address spaces. I did it way down in the TLB handling functions because not everybody goes through flush_tlb_func_common() to flush kernel addresses. I used the variable instead of just invalidating the contexts directly because I hooked into the __flush_tlb_single() path and it's used in loops like this: for (addr = start; addr < end; addr++) __flush_tlb_single() I didn't want to add a loop that effectively does: for (addr = start; addr < end; addr++) __flush_tlb_single(); for (i = 0; i < TLB_NR_DYN_ASIDS; i++) this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0); Even with just 6 ASIDS it seemed a little silly. It would get _very_ silly if we ever decided to grow TLB_NR_DYN_ASIDS.