From patchwork Mon Dec 6 19:54:09 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej S. Szmigiero" X-Patchwork-Id: 12659603 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B11FCC433EF for ; Mon, 6 Dec 2021 19:55:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348925AbhLFT7A (ORCPT ); Mon, 6 Dec 2021 14:59:00 -0500 Received: from vps-vb.mhejs.net ([37.28.154.113]:49812 "EHLO vps-vb.mhejs.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348865AbhLFT6z (ORCPT ); Mon, 6 Dec 2021 14:58:55 -0500 Received: from MUA by vps-vb.mhejs.net with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1muK4f-0000kc-Fr; Mon, 06 Dec 2021 20:54:57 +0100 From: "Maciej S. Szmigiero" To: Paolo Bonzini , Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Igor Mammedov , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandru Elisei , Ben Gardon , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v7 03/29] KVM: Resync only arch fields when slots_arch_lock gets reacquired Date: Mon, 6 Dec 2021 20:54:09 +0100 Message-Id: X-Mailer: git-send-email 2.33.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: "Maciej S. Szmigiero" There is no need to copy the whole memslot data after releasing slots_arch_lock for a moment to install temporary memslots copy in kvm_set_memslot() since this lock only protects the arch field of each memslot. Just resync this particular field after reacquiring slots_arch_lock. Note, this also eliminates the need to manually clear the INVALID flag when restoring memslots; the "setting" of the INVALID flag was an unwanted side effect of copying the entire memslots. Since kvm_copy_memslots() has just one caller remaining now open-code it instead. Signed-off-by: Maciej S. Szmigiero [sean: tweak shortlog, note INVALID flag in changelog, revert comment] Reviewed-by: Sean Christopherson --- virt/kvm/kvm_main.c | 45 +++++++++++++++++++++++++-------------------- 1 file changed, 25 insertions(+), 20 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 049f98238992..95616392ff91 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1517,12 +1517,6 @@ static size_t kvm_memslots_size(int slots) (sizeof(struct kvm_memory_slot) * slots); } -static void kvm_copy_memslots(struct kvm_memslots *to, - struct kvm_memslots *from) -{ - memcpy(to, from, kvm_memslots_size(from->used_slots)); -} - /* * Note, at a minimum, the current number of used slots must be allocated, even * when deleting a memslot, as we need a complete duplicate of the memslots for @@ -1541,11 +1535,22 @@ static struct kvm_memslots *kvm_dup_memslots(struct kvm_memslots *old, slots = kvzalloc(new_size, GFP_KERNEL_ACCOUNT); if (likely(slots)) - kvm_copy_memslots(slots, old); + memcpy(slots, old, kvm_memslots_size(old->used_slots)); return slots; } +static void kvm_copy_memslots_arch(struct kvm_memslots *to, + struct kvm_memslots *from) +{ + int i; + + WARN_ON_ONCE(to->used_slots != from->used_slots); + + for (i = 0; i < from->used_slots; i++) + to->memslots[i].arch = from->memslots[i].arch; +} + static int kvm_set_memslot(struct kvm *kvm, const struct kvm_userspace_memory_region *mem, struct kvm_memory_slot *new, int as_id, @@ -1586,9 +1591,10 @@ static int kvm_set_memslot(struct kvm *kvm, slot->flags |= KVM_MEMSLOT_INVALID; /* - * We can re-use the memory from the old memslots. - * It will be overwritten with a copy of the new memslots - * after reacquiring the slots_arch_lock below. + * We can re-use the old memslots, the only difference from the + * newly installed memslots is the invalid flag, which will get + * dropped by update_memslots anyway. We'll also revert to the + * old memslots if preparing the new memory region fails. */ slots = install_new_memslots(kvm, as_id, slots); @@ -1605,12 +1611,14 @@ static int kvm_set_memslot(struct kvm *kvm, mutex_lock(&kvm->slots_arch_lock); /* - * The arch-specific fields of the memslots could have changed - * between releasing the slots_arch_lock in - * install_new_memslots and here, so get a fresh copy of the - * slots. + * The arch-specific fields of the now-active memslots could + * have been modified between releasing slots_arch_lock in + * install_new_memslots and re-acquiring slots_arch_lock above. + * Copy them to the inactive memslots. Arch code is required + * to retrieve memslots *after* acquiring slots_arch_lock, thus + * the active memslots are guaranteed to be fresh. */ - kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id)); + kvm_copy_memslots_arch(slots, __kvm_memslots(kvm, as_id)); } /* @@ -1659,13 +1667,10 @@ static int kvm_set_memslot(struct kvm *kvm, return 0; out_slots: - if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) { - slot = id_to_memslot(slots, new->id); - slot->flags &= ~KVM_MEMSLOT_INVALID; + if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) slots = install_new_memslots(kvm, as_id, slots); - } else { + else mutex_unlock(&kvm->slots_arch_lock); - } kvfree(slots); return r; }