linux-kernel - [PATCH 5/6] KVM: x86/mmu: Protect kvm->memslots with a mutex

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Date:   Tue, 27 Apr 2021 15:36:34 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 5/6] KVM: x86/mmu: Protect kvm->memslots with a mutex

Adds a lock around memslots changes. Currently this lock does not have
any effect on the syncronization model, but it will be used in a future
commit to facilitate lazy rmap allocation.

Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  5 +++++
 arch/x86/kvm/x86.c              | 11 +++++++++++
 include/linux/kvm_host.h        |  2 ++
 virt/kvm/kvm_main.c             |  9 ++++++++-
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3900dcf2439e..bce7fa152473 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1124,6 +1124,11 @@ struct kvm_arch {
 #endif /* CONFIG_X86_64 */
 
 	bool shadow_mmu_active;
+
+	/*
+	 * Protects kvm->memslots.
+	 */
+	struct mutex memslot_assignment_lock;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fc32a7dbe4c4..30234fe96f48 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10649,6 +10649,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	raw_spin_lock_init(&kvm->arch.tsc_write_lock);
 	mutex_init(&kvm->arch.apic_map_lock);
 	spin_lock_init(&kvm->arch.pvclock_gtod_sync_lock);
+	mutex_init(&kvm->arch.memslot_assignment_lock);
 
 	kvm->arch.kvmclock_offset = -get_kvmclock_base_ns();
 	pvclock_update_vm_gtod_copy(kvm);
@@ -10868,6 +10869,16 @@ static int alloc_memslot_rmap(struct kvm_memory_slot *slot,
 	return -ENOMEM;
 }
 
+
+void kvm_arch_assign_memslots(struct kvm *kvm, int as_id,
+			     struct kvm_memslots *slots)
+{
+	mutex_lock(&kvm->arch.memslot_assignment_lock);
+	rcu_assign_pointer(kvm->memslots[as_id], slots);
+	mutex_unlock(&kvm->arch.memslot_assignment_lock);
+}
+
+
 static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
 				      unsigned long npages)
 {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8895b95b6a22..146bb839c754 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -720,6 +720,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				struct kvm_memory_slot *memslot,
 				const struct kvm_userspace_memory_region *mem,
 				enum kvm_mr_change change);
+void kvm_arch_assign_memslots(struct kvm *kvm, int as_id,
+			     struct kvm_memslots *slots);
 void kvm_arch_commit_memory_region(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
 				struct kvm_memory_slot *old,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2799c6660cce..e62a37bc5b90 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1270,6 +1270,12 @@ static int check_memory_region_flags(const struct kvm_userspace_memory_region *m
 	return 0;
 }
 
+__weak void kvm_arch_assign_memslots(struct kvm *kvm, int as_id,
+				    struct kvm_memslots *slots)
+{
+	rcu_assign_pointer(kvm->memslots[as_id], slots);
+}
+
 static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
 		int as_id, struct kvm_memslots *slots)
 {
@@ -1279,7 +1285,8 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
 	WARN_ON(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS);
 	slots->generation = gen | KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS;
 
-	rcu_assign_pointer(kvm->memslots[as_id], slots);
+	kvm_arch_assign_memslots(kvm, as_id, slots);
+
 	synchronize_srcu_expedited(&kvm->srcu);
 
 	/*
-- 
2.31.1.498.g6c1eba8ee3d-goog