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 X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8EE94C35250 for ; Fri, 7 Feb 2020 18:33:34 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6A66221775 for ; Fri, 7 Feb 2020 18:33:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="IYPEe5CM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A66221775 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=vA39i/vfukQ3vXpv26eMwy2RC9KiIsoUPUXo3zST960=; b=IYPEe5CMl4ad+Z yACIqYtywCp653Pz4L/3i4C+Q5GKwWWRn5BJsVlZVTW/Fa9BbldUGE1AXwDMCCAfOeheocM0U0RzS mTwvvTZ/FWNdqKqg1WfmPaqOyMZkG3A6wXFu4MAQCkC1Th3w5dw8HUKJ7tPsQKTNNBTzlg0bK6eEm 8mgZeFxNDHWgVisJqVYQ2DyOx0nWCYDTR0iNfxXWQ4EqUznK33QHbasmxHM6isddzyN/b+MrHRmUp S3QZEiAmaqMioGbEF7Une0MeXVQ+1LhXR2GVV1o/k7+ioAmzgdUucyaGyhmAAz1aAnfCXrvsoOg43 +J1LLzFTANI5p68s0z0Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1j08RX-0007X4-1p; Fri, 07 Feb 2020 18:33:31 +0000 Received: from mga09.intel.com ([134.134.136.24]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1j08RU-0007WX-8D for linux-arm-kernel@lists.infradead.org; Fri, 07 Feb 2020 18:33:29 +0000 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Feb 2020 10:33:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,414,1574150400"; d="scan'208";a="430918451" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga005.fm.intel.com with ESMTP; 07 Feb 2020 10:33:25 -0800 Date: Fri, 7 Feb 2020 10:33:25 -0800 From: Sean Christopherson To: Peter Xu Subject: Re: [PATCH v5 17/19] KVM: Terminate memslot walks via used_slots Message-ID: <20200207183325.GI2401@linux.intel.com> References: <20200121223157.15263-1-sean.j.christopherson@intel.com> <20200121223157.15263-18-sean.j.christopherson@intel.com> <20200206210944.GD700495@xz-x1> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200206210944.GD700495@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200207_103328_346369_69133460 X-CRM114-Status: GOOD ( 27.83 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-mips@vger.kernel.org, Paul Mackerras , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Christian Borntraeger , Julien Thierry , Suzuki K Poulose , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jim Mattson , Cornelia Huck , Christoffer Dall , linux-kernel@vger.kernel.org, James Morse , Paolo Bonzini , Vitaly Kuznetsov , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Feb 06, 2020 at 04:09:44PM -0500, Peter Xu wrote: > On Tue, Jan 21, 2020 at 02:31:55PM -0800, Sean Christopherson wrote: > > @@ -9652,13 +9652,13 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > > if (IS_ERR((void *)hva)) > > return PTR_ERR((void *)hva); > > } else { > > - if (!slot->npages) > > + if (!slot || !slot->npages) > > return 0; > > > > - hva = 0; > > + hva = slot->userspace_addr; > > Is this intended? Yes. It's possible to allow VA=0 for userspace mappings. It's extremely uncommon, but possible. Therefore "hva == 0" shouldn't be used to indicate an invalid slot. > > + old_npages = slot->npages; > > } > > > > - old = *slot; > > for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { > > struct kvm_userspace_memory_region m; > > ... > > @@ -869,63 +869,162 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot) > > } > > > > /* > > - * Insert memslot and re-sort memslots based on their GFN, > > - * so binary search could be used to lookup GFN. > > - * Sorting algorithm takes advantage of having initially > > - * sorted array and known changed memslot position. > > + * Delete a memslot by decrementing the number of used slots and shifting all > > + * other entries in the array forward one spot. > > + */ > > +static inline void kvm_memslot_delete(struct kvm_memslots *slots, > > + struct kvm_memory_slot *memslot) > > +{ > > + struct kvm_memory_slot *mslots = slots->memslots; > > + int i; > > + > > + if (WARN_ON(slots->id_to_index[memslot->id] == -1)) > > + return; > > + > > + slots->used_slots--; > > + > > + for (i = slots->id_to_index[memslot->id]; i < slots->used_slots; i++) { > > + mslots[i] = mslots[i + 1]; > > + slots->id_to_index[mslots[i].id] = i; > > + } > > + mslots[i] = *memslot; > > + slots->id_to_index[memslot->id] = -1; > > +} > > + > > +/* > > + * "Insert" a new memslot by incrementing the number of used slots. Returns > > + * the new slot's initial index into the memslots array. > > + */ > > +static inline int kvm_memslot_insert_back(struct kvm_memslots *slots) > > The naming here didn't help me to understand but a bit more > confused... > > How about "kvm_memslot_insert_end"? Or even unwrap it. It's not guaranteed to be the end, as there could be multiple unused entries at the back of the array. I agree the naming isn't perfect, but IMO it's the least crappy option and will be familiar to anyone with C++ STL (and other languages?) experience. Arguably it would be better to follow kernel naming for lists, e.g. head/tail, but there are no convenient adverbs for the move helpers, e.g. kvm_memslot_move_backward() would be kvm_memslot_move_towards_tail(). I'm very strongly opposed to unwrapping it. The code would look like this. Without a beefy comment, the high level semantics of the KVM_MR_CREATE case are not at all clear. Adding a comment gets messy because putting it above the entire if-else makes it difficult to understand that its *only* for the CREATE case, and I hate having multi-line comments in if-else statements without brackets. if (change == KVM_MR_CREATE) i = slots->used_slots++ else i = kvm_memslot_move_backward(slots, memslot); > > +{ > > + return slots->used_slots++; > > +} > > + > > +/* > > + * Move a changed memslot backwards in the array by shifting existing slots > > + * with a higher GFN toward the front of the array. Note, the changed memslot > > + * itself is not preserved in the array, i.e. not swapped at this time, only > > + * its new index into the array is tracked. Returns the changed memslot's > > + * current index into the memslots array. > > + */ > > +static inline int kvm_memslot_move_backward(struct kvm_memslots *slots, > > + struct kvm_memory_slot *memslot) > > "backward" makes me feel like it's moving towards smaller index, > instead it's moving to bigger index. Same applies to "forward" below. > I'm not sure whether I'm the only one, though... Move forward towards the front, and backward towards the back. In the languages I am familiar with, e.g. C++ STL, JavaScript, Python, and Golang, front==container[0] and back==container[len() - 1]. > > +{ > > + struct kvm_memory_slot *mslots = slots->memslots; > > + int i; > > + > > + if (WARN_ON_ONCE(slots->id_to_index[memslot->id] == -1) || > > + WARN_ON_ONCE(!slots->used_slots)) > > + return -1; > > + > > + /* > > + * Move the target memslot backward in the array by shifting existing > > + * memslots with a higher GFN (than the target memslot) towards the > > + * front of the array. > > + */ > > + for (i = slots->id_to_index[memslot->id]; i < slots->used_slots - 1; i++) { > > + if (memslot->base_gfn > mslots[i + 1].base_gfn) > > + break; > > + > > + WARN_ON_ONCE(memslot->base_gfn == mslots[i + 1].base_gfn); > > Will this trigger? Note that in __kvm_set_memory_region() we have > already checked overlap of memslots. If you screw up the code it will :-) In a perfect world, no WARN() will *ever* trigger. All of the added WARN_ON_ONCE() are to help the next poor soul that wants to modify this code. > > + > > + /* Shift the next memslot forward one and update its index. */ > > + mslots[i] = mslots[i + 1]; > > + slots->id_to_index[mslots[i].id] = i; > > + } > > + return i; > > +} > > @@ -1104,8 +1203,13 @@ int __kvm_set_memory_region(struct kvm *kvm, ... > > * when the memslots are re-sorted by update_memslots(). > > */ > > tmp = id_to_memslot(__kvm_memslots(kvm, as_id), id); > > - old = *tmp; > > - tmp = NULL; > > I was confused in that patch, then... > > > + if (tmp) { > > + old = *tmp; > > + tmp = NULL; > > ... now I still don't know why it needs to set to NULL? To make it abundantly clear that though shall not use @tmp, i.e. to force using the copy and not the pointer. Note, @tmp is also reused as an iterator below. > > > + } else { > > + memset(&old, 0, sizeof(old)); > > + old.id = id; > > + } > > > > if (!mem->memory_size) > > return kvm_delete_memslot(kvm, mem, &old, as_id); > > @@ -1223,7 +1327,7 @@ int kvm_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log, > > > > slots = __kvm_memslots(kvm, as_id); > > *memslot = id_to_memslot(slots, id); > > - if (!(*memslot)->dirty_bitmap) > > + if (!(*memslot) || !(*memslot)->dirty_bitmap) > > return -ENOENT; > > > > kvm_arch_sync_dirty_log(kvm, *memslot); > > @@ -1281,10 +1385,10 @@ static int kvm_get_dirty_log_protect(struct kvm *kvm, struct kvm_dirty_log *log) > > > > slots = __kvm_memslots(kvm, as_id); > > memslot = id_to_memslot(slots, id); > > + if (!memslot || !memslot->dirty_bitmap) > > + return -ENOENT; > > > > dirty_bitmap = memslot->dirty_bitmap; > > - if (!dirty_bitmap) > > - return -ENOENT; > > > > kvm_arch_sync_dirty_log(kvm, memslot); > > > > @@ -1392,10 +1496,10 @@ static int kvm_clear_dirty_log_protect(struct kvm *kvm, > > > > slots = __kvm_memslots(kvm, as_id); > > memslot = id_to_memslot(slots, id); > > + if (!memslot || !memslot->dirty_bitmap) > > + return -ENOENT; > > > > dirty_bitmap = memslot->dirty_bitmap; > > - if (!dirty_bitmap) > > - return -ENOENT; > > > > n = ALIGN(log->num_pages, BITS_PER_LONG) / 8; > > > > -- > > 2.24.1 > > > > -- > Peter Xu > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel