pve-kernel-lowlatency-qoup/patches/kernel/0008-KVM-Take-vcpu-mutex-outside-vcpu_load.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Christoffer Dall <christoffer.dall@linaro.org>
Date: Mon, 4 Dec 2017 21:35:23 +0100
Subject: [PATCH] KVM: Take vcpu->mutex outside vcpu_load

As we're about to call vcpu_load() from architecture-specific
implementations of the KVM vcpu ioctls, but yet we access data
structures protected by the vcpu->mutex in the generic code, factor
this logic out from vcpu_load().

x86 is the only architecture which calls vcpu_load() outside of the main
vcpu ioctl function, and these calls will no longer take the vcpu mutex
following this patch.  However, with the exception of
kvm_arch_vcpu_postcreate (see below), the callers are either in the
creation or destruction path of the VCPU, which means there cannot be
any concurrent access to the data structure, because the file descriptor
is not yet accessible, or is already gone.

kvm_arch_vcpu_postcreate makes the newly created vcpu potentially
accessible by other in-kernel threads through the kvm->vcpus array, and
we therefore take the vcpu mutex in this case directly.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit ec7660ccdd2b71d8c7f0243f8590253713e9b75d)
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
 arch/x86/kvm/vmx.c       |  4 +---
 arch/x86/kvm/x86.c       | 20 +++++++-------------
 include/linux/kvm_host.h |  2 +-
 virt/kvm/kvm_main.c      | 17 ++++++-----------
 4 files changed, 15 insertions(+), 28 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fbaae82d3025..521f8d0632fb 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10015,10 +10015,8 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
 static void vmx_free_vcpu_nested(struct kvm_vcpu *vcpu)
 {
        struct vcpu_vmx *vmx = to_vmx(vcpu);
-       int r;
 
-       r = vcpu_load(vcpu);
-       BUG_ON(r);
+       vcpu_load(vcpu);
        vmx_switch_vmcs(vcpu, &vmx->vmcs01);
        free_nested(vmx);
        vcpu_put(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 012bfad459ed..e42319badda3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8037,17 +8037,13 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
 
 int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 {
-	int r;
-
 	vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
 	kvm_vcpu_mtrr_init(vcpu);
-	r = vcpu_load(vcpu);
-	if (r)
-		return r;
+	vcpu_load(vcpu);
 	kvm_vcpu_reset(vcpu, false);
 	kvm_mmu_setup(vcpu);
 	vcpu_put(vcpu);
-	return r;
+	return 0;
 }
 
 void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
@@ -8057,13 +8053,15 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 
 	kvm_hv_vcpu_postcreate(vcpu);
 
-	if (vcpu_load(vcpu))
+	if (mutex_lock_killable(&vcpu->mutex))
 		return;
+	vcpu_load(vcpu);
 	msr.data = 0x0;
 	msr.index = MSR_IA32_TSC;
 	msr.host_initiated = true;
 	kvm_write_tsc(vcpu, &msr);
 	vcpu_put(vcpu);
+	mutex_unlock(&vcpu->mutex);
 
 	if (!kvmclock_periodic_sync)
 		return;
@@ -8074,11 +8072,9 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 {
-	int r;
 	vcpu->arch.apf.msr_val = 0;
 
-	r = vcpu_load(vcpu);
-	BUG_ON(r);
+	vcpu_load(vcpu);
 	kvm_mmu_unload(vcpu);
 	vcpu_put(vcpu);
 
@@ -8458,9 +8454,7 @@ int kvm_arch_post_init_vm(struct kvm *kvm)
 
 static void kvm_unload_vcpu_mmu(struct kvm_vcpu *vcpu)
 {
-	int r;
-	r = vcpu_load(vcpu);
-	BUG_ON(r);
+	vcpu_load(vcpu);
 	kvm_mmu_unload(vcpu);
 	vcpu_put(vcpu);
 }
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 927d0002d9c9..f2c024661513 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -534,7 +534,7 @@ static inline int kvm_vcpu_get_idx(struct kvm_vcpu *vcpu)
 int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id);
 void kvm_vcpu_uninit(struct kvm_vcpu *vcpu);
 
-int __must_check vcpu_load(struct kvm_vcpu *vcpu);
+void vcpu_load(struct kvm_vcpu *vcpu);
 void vcpu_put(struct kvm_vcpu *vcpu);
 
 #ifdef __KVM_HAVE_IOAPIC
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a715074f424e..010c6366a1d5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -152,17 +152,12 @@ bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
 /*
  * Switches to specified vcpu, until a matching vcpu_put()
  */
-int vcpu_load(struct kvm_vcpu *vcpu)
+void vcpu_load(struct kvm_vcpu *vcpu)
 {
-	int cpu;
-
-	if (mutex_lock_killable(&vcpu->mutex))
-		return -EINTR;
-	cpu = get_cpu();
+	int cpu = get_cpu();
 	preempt_notifier_register(&vcpu->preempt_notifier);
 	kvm_arch_vcpu_load(vcpu, cpu);
 	put_cpu();
-	return 0;
 }
 EXPORT_SYMBOL_GPL(vcpu_load);
 
@@ -172,7 +167,6 @@ void vcpu_put(struct kvm_vcpu *vcpu)
 	kvm_arch_vcpu_put(vcpu);
 	preempt_notifier_unregister(&vcpu->preempt_notifier);
 	preempt_enable();
-	mutex_unlock(&vcpu->mutex);
 }
 EXPORT_SYMBOL_GPL(vcpu_put);
 
@@ -2619,9 +2613,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
 #endif
 
 
-	r = vcpu_load(vcpu);
-	if (r)
-		return r;
+	if (mutex_lock_killable(&vcpu->mutex))
+		return -EINTR;
+	vcpu_load(vcpu);
 	switch (ioctl) {
 	case KVM_RUN: {
 		struct pid *oldpid;
@@ -2794,6 +2788,7 @@ static long kvm_vcpu_ioctl(struct file *filp,
 	}
 out:
 	vcpu_put(vcpu);
+	mutex_unlock(&vcpu->mutex);
 	kfree(fpu);
 	kfree(kvm_sregs);
 	return r;