From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 95EFDC433F5 for ; Thu, 6 Jan 2022 12:51:25 +0000 (UTC) Received: from localhost ([::1]:48680 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n5SEm-0006no-Mp for qemu-devel@archiver.kernel.org; Thu, 06 Jan 2022 07:51:24 -0500 Received: from eggs.gnu.org ([209.51.188.92]:59076) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n5S0E-0008Ip-Me for qemu-devel@nongnu.org; Thu, 06 Jan 2022 07:36:22 -0500 Received: from mga01.intel.com ([192.55.52.88]:57509) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n5S08-0001Yf-65 for qemu-devel@nongnu.org; Thu, 06 Jan 2022 07:36:22 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1641472576; x=1673008576; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=xyua25iDh4JWOKyPASiZgoHVEXaKTA4j0IhBTE9lILI=; b=SciRVyFpKGnodeZWCzVcK9lphVhyw8T0QyBA7GbxsD5vfAfEHsZdZK5F 4rbiWrMsvFAMQfJMgMbHDZXTD1sDtJ2NcDPI/KsASX0pJeIzOPgDQeVQL he7ioFlFwq4WST1uzkE+MmqeWazxwu4i37aL49WlhLIhGTDYzBT1hHgWO 82kIJdz2JihYmj9ILpVvG4ONnOVIuAwW2sbzqK3rBWTKMfv8mMf0eLY6L tIWZ5bwpF/l+NCpMd5TxwGr8J8DpQiZbwGOt3RhWYZydRYhRP0A++ck5Y OCgxscdxumyt8zHWe+x2F5tqCB5vtjKw5PwJQfe5LXj3a1tigCf4Yh3ZY Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10217"; a="266936204" X-IronPort-AV: E=Sophos;i="5.88,267,1635231600"; d="scan'208";a="266936204" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jan 2022 04:36:11 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.88,267,1635231600"; d="scan'208";a="472880803" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.192.101]) by orsmga006.jf.intel.com with ESMTP; 06 Jan 2022 04:35:59 -0800 Date: Thu, 6 Jan 2022 20:35:25 +0800 From: Chao Peng To: Sean Christopherson Subject: Re: [PATCH v3 kvm/queue 11/16] KVM: Add kvm_map_gfn_range Message-ID: <20220106123525.GA43371@chaop.bj.intel.com> References: <20211223123011.41044-1-chao.p.peng@linux.intel.com> <20211223123011.41044-12-chao.p.peng@linux.intel.com> <20211224041351.GB44042@chaop.bj.intel.com> <20211231023334.GA7255@chaop.bj.intel.com> <20220105061410.GA25283@chaop.bj.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Received-SPF: none client-ip=192.55.52.88; envelope-from=chao.p.peng@linux.intel.com; helo=mga01.intel.com X-Spam_score_int: -73 X-Spam_score: -7.4 X-Spam_bar: ------- X-Spam_report: (-7.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.372, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Chao Peng Cc: Wanpeng Li , jun.nakajima@intel.com, kvm@vger.kernel.org, david@redhat.com, qemu-devel@nongnu.org, "J . Bruce Fields" , linux-mm@kvack.org, "H . Peter Anvin" , ak@linux.intel.com, Jonathan Corbet , Joerg Roedel , x86@kernel.org, Hugh Dickins , Ingo Molnar , Borislav Petkov , luto@kernel.org, Thomas Gleixner , Vitaly Kuznetsov , Jim Mattson , dave.hansen@intel.com, susie.li@intel.com, Jeff Layton , linux-kernel@vger.kernel.org, john.ji@intel.com, Yu Zhang , linux-fsdevel@vger.kernel.org, Paolo Bonzini , Andrew Morton , "Kirill A . Shutemov" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jan 05, 2022 at 05:03:23PM +0000, Sean Christopherson wrote: > On Wed, Jan 05, 2022, Chao Peng wrote: > > On Tue, Jan 04, 2022 at 05:31:30PM +0000, Sean Christopherson wrote: > > > On Fri, Dec 31, 2021, Chao Peng wrote: > > > > On Fri, Dec 24, 2021 at 12:13:51PM +0800, Chao Peng wrote: > > > > > On Thu, Dec 23, 2021 at 06:06:19PM +0000, Sean Christopherson wrote: > > > > > > On Thu, Dec 23, 2021, Chao Peng wrote: > > > > > > > This new function establishes the mapping in KVM page tables for a > > > > > > > given gfn range. It can be used in the memory fallocate callback for > > > > > > > memfd based memory to establish the mapping for KVM secondary MMU when > > > > > > > the pages are allocated in the memory backend. > > > > > > > > > > > > NAK, under no circumstance should KVM install SPTEs in response to allocating > > > > > > memory in a file. The correct thing to do is to invalidate the gfn range > > > > > > associated with the newly mapped range, i.e. wipe out any shared SPTEs associated > > > > > > with the memslot. > > > > > > > > > > Right, thanks. > > > > > > > > BTW, I think the current fallocate() callback is just useless as long as > > > > we don't want to install KVM SPTEs in response to allocating memory in a > > > > file. The invalidation of the shared SPTEs should be notified through > > > > mmu_notifier of the shared memory backend, not memfd_notifier of the > > > > private memory backend. > > > > > > No, because the private fd is the final source of truth as to whether or not a > > > GPA is private, e.g. userspace may choose to not unmap the shared backing. > > > KVM's rule per Paolo's/this proposoal is that a GPA is private if it has a private > > > memslot and is present in the private backing store. And the other core rule is > > > that KVM must never map both the private and shared variants of a GPA into the > > > guest. > > > > That's true, but I'm wondering if zapping the shared variant can be > > handled at the time when the private one gets mapped in the KVM page > > fault. No bothering the backing store to dedicate a callback to tell > > KVM. > > Hmm, I don't think that would work for the TDP MMU due to page faults taking > mmu_lock for read. E.g. if two vCPUs concurrently fault in both the shared and > private variants, a race could exist where the private page fault sees the gfn > as private and the shared page fault sees it as shared. In that case, both faults > will install a SPTE and KVM would end up running with both variants mapped into the > guest. > > There's also a performance penalty, as KVM would need to walk the shared EPT tree > on every private page fault. Make sense. Thanks, Chao