From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Date: Thu, 04 Nov 2021 00:25:06 +0000 Subject: [PATCH v5.5 05/30] KVM: Resync only arch fields when slots_arch_lock gets reacquired Message-Id: <20211104002531.1176691-6-seanjc@google.com> List-Id: References: <20211104002531.1176691-1-seanjc@google.com> In-Reply-To: <20211104002531.1176691-1-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini Cc: Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, Atish Patra , Ben Gardon , "Maciej S . Szmigiero" , Claudio Imbrenda , linux-riscv@lists.infradead.org, Joerg Roedel , kvmarm@lists.cs.columbia.edu, kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jim Mattson , Cornelia Huck , linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, Vitaly Kuznetsov 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. Signed-off-by: Maciej S. Szmigiero [sean: tweak shortlog, note INVALID flag in changelog, revert comment] Signed-off-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 6171ddb3e31c..e5c2d10f6111 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1500,12 +1500,6 @@ 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 @@ -1524,11 +1518,22 @@ 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, @@ -1569,9 +1574,10 @@ 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); @@ -1588,12 +1594,14 @@ 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)); } /* @@ -1642,13 +1650,10 @@ 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; } -- 2.33.1.1089.g2158813163f-goog