Re: [PATCH V11 2/5] KVM: SEV: Add support for SEV intra host migration

[Paolo Bonzini]

On 11/4/21 23:07, Sean Christopherson wrote:
> That would also provide a good opportunity to more tightly couple ->asid and
> ->misc_cg in the form of a helper.  Looking at the code, there's an invariant
> that misc_cg is NULL if an ASID is not assigned.  I.e. these three lines belong
> in a helper, irrespective of this code.
>
> 	misc_cg_uncharge(type, sev->misc_cg, 1);
> 	put_misc_cg(sev->misc_cg);
> 	sev->misc_cg = NULL;

Agreed.  Though it's a bit more complicated because if dst->misc_cg ==
src->misc_cg you should *not* charge and uncharge, because charging
could fail.  So I'm going for just simple charge/uncharge helpers for
now:

From 0ac1004d9e15e9460b51651bd095e6c5ee9cf4f9 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Thu, 11 Nov 2021 10:02:26 -0500
Subject: [PATCH 1/4] KVM: SEV: provide helpers to charge/uncharge misc_cg

Avoid code duplication across all callers of misc_cg_try_charge and
misc_cg_uncharge.  The resource type for KVM is always derived from
sev->es_active, and the quantity is always 1.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7c94fe307b39..5bafa4bf7c49 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -120,16 +120,26 @@ static bool __sev_recycle_asids(int min_asid, int max_asid)
 	return true;
 }
 
+static int sev_misc_cg_try_charge(struct kvm_sev_info *sev)
+{
+	enum misc_res_type type = sev->es_active ? MISC_CG_RES_SEV_ES : MISC_CG_RES_SEV;
+	return misc_cg_try_charge(type, sev->misc_cg, 1);
+}
+
+static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
+{
+	enum misc_res_type type = sev->es_active ? MISC_CG_RES_SEV_ES : MISC_CG_RES_SEV;
+	misc_cg_uncharge(type, sev->misc_cg, 1);
+}
+
 static int sev_asid_new(struct kvm_sev_info *sev)
 {
 	int asid, min_asid, max_asid, ret;
 	bool retry = true;
-	enum misc_res_type type;
 
-	type = sev->es_active ? MISC_CG_RES_SEV_ES : MISC_CG_RES_SEV;
 	WARN_ON(sev->misc_cg);
 	sev->misc_cg = get_current_misc_cg();
-	ret = misc_cg_try_charge(type, sev->misc_cg, 1);
+	ret = sev_misc_cg_try_charge(sev);
 	if (ret) {
 		put_misc_cg(sev->misc_cg);
 		sev->misc_cg = NULL;
@@ -162,7 +172,7 @@ static int sev_asid_new(struct kvm_sev_info *sev)
 
 	return asid;
 e_uncharge:
-	misc_cg_uncharge(type, sev->misc_cg, 1);
+	sev_misc_cg_uncharge(sev);
 	put_misc_cg(sev->misc_cg);
 	sev->misc_cg = NULL;
 	return ret;
@@ -179,7 +189,6 @@ static void sev_asid_free(struct kvm_sev_info *sev)
 {
 	struct svm_cpu_data *sd;
 	int cpu;
-	enum misc_res_type type;
 
 	mutex_lock(&sev_bitmap_lock);
 
@@ -192,8 +201,7 @@ static void sev_asid_free(struct kvm_sev_info *sev)
 
 	mutex_unlock(&sev_bitmap_lock);
 
-	type = sev->es_active ? MISC_CG_RES_SEV_ES : MISC_CG_RES_SEV;
-	misc_cg_uncharge(type, sev->misc_cg, 1);
+	sev_misc_cg_uncharge(sev);
 	put_misc_cg(sev->misc_cg);
 	sev->misc_cg = NULL;
 }



From 5214132ae7e8310de26d5791f7fe913085a8e53c Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Thu, 11 Nov 2021 10:08:32 -0500
Subject: [PATCH 2/4] fix cgroup charging


diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5bafa4bf7c49..97048ff7c2ad 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1594,7 +1594,6 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
 {
 	dst->active = true;
 	dst->asid = src->asid;
-	dst->misc_cg = src->misc_cg;
 	dst->handle = src->handle;
 	dst->pages_locked = src->pages_locked;
 
@@ -1602,6 +1601,11 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
 	src->active = false;
 	src->handle = 0;
 	src->pages_locked = 0;
+
+	if (dst->misc_cg != src->misc_cg)
+		sev_misc_cg_uncharge(src);
+
+	put_misc_cg(src->misc_cg);
 	src->misc_cg = NULL;
 
 	INIT_LIST_HEAD(&dst->regions_list);
@@ -1611,6 +1615,7 @@ static void sev_migrate_from(struct kvm_sev_info *dst,
 int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
 {
 	struct kvm_sev_info *dst_sev = &to_kvm_svm(kvm)->sev_info;
+	struct kvm_sev_info *src_sev;
 	struct file *source_kvm_file;
 	struct kvm *source_kvm;
 	struct kvm_vcpu *vcpu;
@@ -1640,25 +1645,39 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
 		ret = -EINVAL;
 		goto out_source;
 	}
+
+	src_sev = &to_kvm_svm(source_kvm)->sev_info;
+	dst_sev->misc_cg = get_current_misc_cg();
+	if (dst_sev->misc_cg != src_sev->misc_cg) {
+		ret = sev_misc_cg_try_charge(dst_sev);
+		if (ret)
+			goto out_dst_put_cgroup;
+	}
+
 	ret = sev_lock_vcpus_for_migration(kvm);
 	if (ret)
-		goto out_dst_vcpu;
+		goto out_dst_cgroup;
 	ret = sev_lock_vcpus_for_migration(source_kvm);
 	if (ret)
-		goto out_source_vcpu;
+		goto out_dst_vcpu;
 
-	sev_migrate_from(dst_sev, &to_kvm_svm(source_kvm)->sev_info);
+	sev_migrate_from(dst_sev, src_sev);
 	kvm_for_each_vcpu(i, vcpu, source_kvm) {
 		kvm_vcpu_reset(vcpu, /* init_event= */ false);
 	}
 	ret = 0;
 
-out_source_vcpu:
 	sev_unlock_vcpus_for_migration(source_kvm);
 
 out_dst_vcpu:
 	sev_unlock_vcpus_for_migration(kvm);
-
+out_dst_cgroup:
+	if (ret < 0) {
+		sev_misc_cg_uncharge(dst_sev);
+out_dst_put_cgroup:
+		put_misc_cg(dst_sev->misc_cg);
+		dst_sev->misc_cg = NULL;
+	}
 out_source:
 	sev_unlock_after_migration(source_kvm);
 out_fput:



From 943ba93c57ee25f85538decd68dca6e4ebdaf2c1 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Thu, 11 Nov 2021 10:13:38 -0500
Subject: [PATCH 3/4] KVM: generalize "bugged" VM to "dead" VM

Generalize KVM_REQ_VM_BUGGED so that it can be called even in cases
where it is by design that the VM cannot be operated upon.  In this
case any KVM_BUG_ON should still warn, so introduce a new flag
kvm->vm_dead that is separate from kvm->vm_bugged.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ca9693d3436b..185094eb86b6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9660,7 +9660,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	}
 
 	if (kvm_request_pending(vcpu)) {
-		if (kvm_check_request(KVM_REQ_VM_BUGGED, vcpu)) {
+		if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) {
 			r = -EIO;
 			goto out;
 		}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 60a35d9fe259..9e0667e3723e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -150,7 +150,7 @@ static inline bool is_error_page(struct page *page)
 #define KVM_REQ_MMU_RELOAD        (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_UNBLOCK           2
 #define KVM_REQ_UNHALT            3
-#define KVM_REQ_VM_BUGGED         (4 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
+#define KVM_REQ_VM_DEAD           (4 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQUEST_ARCH_BASE     8
 
 #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
@@ -617,6 +617,7 @@ struct kvm {
 	unsigned int max_halt_poll_ns;
 	u32 dirty_ring_size;
 	bool vm_bugged;
+	bool vm_dead;
 
 #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
 	struct notifier_block pm_notifier;
@@ -650,12 +651,19 @@ struct kvm {
 #define vcpu_err(vcpu, fmt, ...)					\
 	kvm_err("vcpu%i " fmt, (vcpu)->vcpu_id, ## __VA_ARGS__)
 
+static inline void kvm_vm_dead(struct kvm *kvm)
+{
+	kvm->vm_dead = true;
+	kvm_make_all_cpus_request(kvm, KVM_REQ_VM_DEAD);
+}
+
 static inline void kvm_vm_bugged(struct kvm *kvm)
 {
 	kvm->vm_bugged = true;
-	kvm_make_all_cpus_request(kvm, KVM_REQ_VM_BUGGED);
+	kvm_vm_dead(kvm);
 }
 
+
 #define KVM_BUG(cond, kvm, fmt...)				\
 ({								\
 	int __ret = (cond);					\
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3f6d450355f0..d31724500501 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3747,7 +3747,7 @@ static long kvm_vcpu_ioctl(struct file *filp,
 	struct kvm_fpu *fpu = NULL;
 	struct kvm_sregs *kvm_sregs = NULL;
 
-	if (vcpu->kvm->mm != current->mm || vcpu->kvm->vm_bugged)
+	if (vcpu->kvm->mm != current->mm || vcpu->kvm->vm_dead)
 		return -EIO;
 
 	if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
@@ -3957,7 +3957,7 @@ static long kvm_vcpu_compat_ioctl(struct file *filp,
 	void __user *argp = compat_ptr(arg);
 	int r;
 
-	if (vcpu->kvm->mm != current->mm || vcpu->kvm->vm_bugged)
+	if (vcpu->kvm->mm != current->mm || vcpu->kvm->vm_dead)
 		return -EIO;
 
 	switch (ioctl) {
@@ -4023,7 +4023,7 @@ static long kvm_device_ioctl(struct file *filp, unsigned int ioctl,
 {
 	struct kvm_device *dev = filp->private_data;
 
-	if (dev->kvm->mm != current->mm || dev->kvm->vm_bugged)
+	if (dev->kvm->mm != current->mm || dev->kvm->vm_dead)
 		return -EIO;
 
 	switch (ioctl) {
@@ -4345,7 +4345,7 @@ static long kvm_vm_ioctl(struct file *filp,
 	void __user *argp = (void __user *)arg;
 	int r;
 
-	if (kvm->mm != current->mm || kvm->vm_bugged)
+	if (kvm->mm != current->mm || kvm->vm_dead)
 		return -EIO;
 	switch (ioctl) {
 	case KVM_CREATE_VCPU:
@@ -4556,7 +4556,7 @@ static long kvm_vm_compat_ioctl(struct file *filp,
 	struct kvm *kvm = filp->private_data;
 	int r;
 
-	if (kvm->mm != current->mm || kvm->vm_bugged)
+	if (kvm->mm != current->mm || kvm->vm_dead)
 		return -EIO;
 	switch (ioctl) {
 #ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT



From fb168352e16a4dbd95a7c0d1e6add18f0496ac97 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Thu, 11 Nov 2021 10:14:49 -0500
Subject: [PATCH 4/4] mark src vm as dead


diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 97048ff7c2ad..2403aea3dbd3 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1662,12 +1662,9 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
 		goto out_dst_vcpu;
 
 	sev_migrate_from(dst_sev, src_sev);
-	kvm_for_each_vcpu(i, vcpu, source_kvm) {
-		kvm_vcpu_reset(vcpu, /* init_event= */ false);
-	}
-	ret = 0;
-
+	kvm_vm_dead(source_kvm);
 	sev_unlock_vcpus_for_migration(source_kvm);
+	ret = 0;
 
 out_dst_vcpu:
 	sev_unlock_vcpus_for_migration(kvm);


I'll send it out properly when I finish reviewing.

Paolo