Re: [RFC][PATCH] reduce KVM stack usage

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Thu, 2008-07-17 at 08:40 -0700, Roland Dreier wrote: 
> > +	struct kvm_pv_mmu_op_buffer *buffer =
>  > +		kmalloc(GFP_KERNEL, sizeof(struct kvm_pv_mmu_op_buffer));
> 
> Surely this produces a warning?  kmalloc takes (size, flags) -- you have
> them reversed here.

Heh.  It actually doesn't.  

> > +		lapic = kzalloc(GFP_KERNEL, sizeof(*lapic));
>  > +		lapic = kmalloc(GFP_KERNEL, sizeof(*lapic));
>  > +	struct kvm_irqchip *chip = kmalloc(GFP_KERNEL, sizeof(*chip));
>  > +		kvm_sregs = kmalloc(GFP_KERNEL, sizeof kvm_sregs);
>  > +		fpu = kmalloc(GFP_KERNEL, sizeof(*fpu));
> 
> same for all of these places.
> 
>  > +	if (lapic)
>  > +		kfree(lapic);
> 
>  > +	if (fpu)
>  > +		kfree(fpu);
>  > +	if (kvm_sregs)
>  > +		kfree(kvm_sregs);
> 
> kfree(NULL) is fine, so you can remove the if()s here.

I know it is fine, but I kinda like putting the if()s, just to let
people know that we don't always *expect* something to be in there.
But, it doesn't matter to me too much either way.

Here's another try.  This actually lets kvm come up for me.

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7e7c396..fd1f303 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2154,18 +2154,24 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
 		  gpa_t addr, unsigned long *ret)
 {
 	int r;
-	struct kvm_pv_mmu_op_buffer buffer;
+	struct kvm_pv_mmu_op_buffer *buffer =
+		kmalloc(sizeof(struct kvm_pv_mmu_op_buffer), GFP_KERNEL);
 
-	buffer.ptr = buffer.buf;
-	buffer.len = min_t(unsigned long, bytes, sizeof buffer.buf);
-	buffer.processed = 0;
+	if (!buffer) {
+		*ret = 0;
+		return -ENOMEM;
+	}
+
+	buffer->ptr = buffer->buf;
+	buffer->len = min_t(unsigned long, bytes, sizeof buffer->buf);
+	buffer->processed = 0;
 
-	r = kvm_read_guest(vcpu->kvm, addr, buffer.buf, buffer.len);
+	r = kvm_read_guest(vcpu->kvm, addr, buffer->buf, buffer->len);
 	if (r)
 		goto out;
 
-	while (buffer.len) {
-		r = kvm_pv_mmu_op_one(vcpu, &buffer);
+	while (buffer->len) {
+		r = kvm_pv_mmu_op_one(vcpu, buffer);
 		if (r < 0)
 			goto out;
 		if (r == 0)
@@ -2174,7 +2180,8 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
 
 	r = 1;
 out:
-	*ret = buffer.processed;
+	*ret = buffer->processed;
+	kfree(buffer);
 	return r;
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0faa254..14eae49 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1283,13 +1283,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	struct kvm_vcpu *vcpu = filp->private_data;
 	void __user *argp = (void __user *)arg;
 	int r;
+	struct kvm_lapic_state *lapic = NULL;
 
 	switch (ioctl) {
 	case KVM_GET_LAPIC: {
-		struct kvm_lapic_state lapic;
+		lapic = kzalloc(sizeof(struct kvm_lapic_state), GFP_KERNEL);
 
-		memset(&lapic, 0, sizeof lapic);
-		r = kvm_vcpu_ioctl_get_lapic(vcpu, &lapic);
+		r = -ENOMEM;
+		if (!lapic)
+			goto out;
+		r = kvm_vcpu_ioctl_get_lapic(vcpu, lapic);
 		if (r)
 			goto out;
 		r = -EFAULT;
@@ -1299,12 +1302,14 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_LAPIC: {
-		struct kvm_lapic_state lapic;
-
+		lapic = kmalloc(sizeof(struct kvm_lapic_state), GFP_KERNEL);
+		r = -ENOMEM;
+		if (!lapic)
+			goto out;
 		r = -EFAULT;
-		if (copy_from_user(&lapic, argp, sizeof lapic))
+		if (copy_from_user(lapic, argp, sizeof(struct kvm_lapic_state)))
 			goto out;
-		r = kvm_vcpu_ioctl_set_lapic(vcpu, &lapic);;
+		r = kvm_vcpu_ioctl_set_lapic(vcpu, lapic);
 		if (r)
 			goto out;
 		r = 0;
@@ -1402,6 +1407,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = -EINVAL;
 	}
 out:
+	kfree(lapic);
 	return r;
 }
 
@@ -1602,12 +1608,73 @@ out:
 	return r;
 }
 
+static int kvm_arch_vm_irqchip_ioctl(struct kvm *kvm, void *argp,
+				     unsigned int ioctl)
+{
+	int ret = 0;
+	struct kvm_irqchip *chip = kmalloc(sizeof(struct kvm_irqchip), GFP_KERNEL);
+
+	if (!chip)
+		return -ENOMEM;
+
+	/* cheaper than the copy, so do this first */
+	if (!irqchip_in_kernel(kvm)) {
+		ret = -ENXIO;
+		goto out;
+	}
+	if (copy_from_user(chip, argp, sizeof(struct kvm_irqchip))) {
+		ret = -EFAULT;
+		goto out;
+	}
+	switch (ioctl) {
+	case KVM_GET_IRQCHIP:
+		ret = kvm_vm_ioctl_get_irqchip(kvm, chip);
+		if (ret)
+			goto out;
+		ret = copy_to_user(argp, chip, sizeof(struct kvm_irqchip));
+		if (ret) {
+			ret = -EFAULT;
+			goto out;
+		}
+		break;
+	case KVM_SET_IRQCHIP:
+		ret = kvm_vm_ioctl_set_irqchip(kvm, chip);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+out:
+	kfree(chip);
+	return ret;
+}
+
+
+int x86_kvm_vm_ioctl_set_memory_region(struct kvm *kvm, void *argp)
+{
+	struct kvm_memory_region kvm_mem;
+	struct kvm_userspace_memory_region kvm_userspace_mem;
+
+	if (copy_from_user(&kvm_mem, argp, sizeof(struct kvm_memory_region)))
+		return -EFAULT;
+	kvm_userspace_mem.slot = kvm_mem.slot;
+	kvm_userspace_mem.flags = kvm_mem.flags;
+	kvm_userspace_mem.guest_phys_addr = kvm_mem.guest_phys_addr;
+	kvm_userspace_mem.memory_size = kvm_mem.memory_size;
+	return kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem, 0);
+}
+
 long kvm_arch_vm_ioctl(struct file *filp,
 		       unsigned int ioctl, unsigned long arg)
 {
 	struct kvm *kvm = filp->private_data;
 	void __user *argp = (void __user *)arg;
 	int r = -EINVAL;
+	union {
+		/* 0: PIC master, 1: PIC slave, 2: IOAPIC */
+		struct kvm_pit_state ps;
+		struct kvm_memory_alias alias;
+	} u;
 
 	switch (ioctl) {
 	case KVM_SET_TSS_ADDR:
@@ -1639,17 +1706,14 @@ long kvm_arch_vm_ioctl(struct file *filp,
 	case KVM_GET_NR_MMU_PAGES:
 		r = kvm_vm_ioctl_get_nr_mmu_pages(kvm);
 		break;
-	case KVM_SET_MEMORY_ALIAS: {
-		struct kvm_memory_alias alias;
-
+	case KVM_SET_MEMORY_ALIAS:
 		r = -EFAULT;
-		if (copy_from_user(&alias, argp, sizeof alias))
+		if (copy_from_user(&u.alias, argp, sizeof(struct kvm_memory_alias)))
 			goto out;
-		r = kvm_vm_ioctl_set_memory_alias(kvm, &alias);
+		r = kvm_vm_ioctl_set_memory_alias(kvm, &u.alias);
 		if (r)
 			goto out;
 		break;
-	}
 	case KVM_CREATE_IRQCHIP:
 		r = -ENOMEM;
 		kvm->arch.vpic = kvm_create_pic(kvm);
@@ -1689,67 +1753,37 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		}
 		break;
 	}
-	case KVM_GET_IRQCHIP: {
-		/* 0: PIC master, 1: PIC slave, 2: IOAPIC */
-		struct kvm_irqchip chip;
-
-		r = -EFAULT;
-		if (copy_from_user(&chip, argp, sizeof chip))
-			goto out;
-		r = -ENXIO;
-		if (!irqchip_in_kernel(kvm))
-			goto out;
-		r = kvm_vm_ioctl_get_irqchip(kvm, &chip);
-		if (r)
-			goto out;
-		r = -EFAULT;
-		if (copy_to_user(argp, &chip, sizeof chip))
-			goto out;
-		r = 0;
-		break;
-	}
-	case KVM_SET_IRQCHIP: {
-		/* 0: PIC master, 1: PIC slave, 2: IOAPIC */
-		struct kvm_irqchip chip;
-
-		r = -EFAULT;
-		if (copy_from_user(&chip, argp, sizeof chip))
-			goto out;
-		r = -ENXIO;
-		if (!irqchip_in_kernel(kvm))
-			goto out;
-		r = kvm_vm_ioctl_set_irqchip(kvm, &chip);
+	case KVM_GET_IRQCHIP:
+	case KVM_SET_IRQCHIP:
+		r = kvm_arch_vm_irqchip_ioctl(kvm, argp, ioctl);
 		if (r)
 			goto out;
 		r = 0;
 		break;
-	}
 	case KVM_GET_PIT: {
-		struct kvm_pit_state ps;
 		r = -EFAULT;
-		if (copy_from_user(&ps, argp, sizeof ps))
+		if (copy_from_user(&u.ps, argp, sizeof(struct kvm_pit_state)))
 			goto out;
 		r = -ENXIO;
 		if (!kvm->arch.vpit)
 			goto out;
-		r = kvm_vm_ioctl_get_pit(kvm, &ps);
+		r = kvm_vm_ioctl_get_pit(kvm, &u.ps);
 		if (r)
 			goto out;
 		r = -EFAULT;
-		if (copy_to_user(argp, &ps, sizeof ps))
+		if (copy_to_user(argp, &u.ps, sizeof(struct kvm_pit_state)))
 			goto out;
 		r = 0;
 		break;
 	}
 	case KVM_SET_PIT: {
-		struct kvm_pit_state ps;
 		r = -EFAULT;
-		if (copy_from_user(&ps, argp, sizeof ps))
+		if (copy_from_user(&u.ps, argp, sizeof u.ps))
 			goto out;
 		r = -ENXIO;
 		if (!kvm->arch.vpit)
 			goto out;
-		r = kvm_vm_ioctl_set_pit(kvm, &ps);
+		r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
 		if (r)
 			goto out;
 		r = 0;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d4eae6a..c31adbb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -905,6 +905,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
 	struct kvm_vcpu *vcpu = filp->private_data;
 	void __user *argp = (void __user *)arg;
 	int r;
+	struct kvm_fpu *fpu = NULL;
+	struct kvm_sregs *kvm_sregs = NULL;
+
 
 	if (vcpu->kvm->mm != current->mm)
 		return -EIO;
@@ -952,25 +955,29 @@ out_free2:
 		break;
 	}
 	case KVM_GET_SREGS: {
-		struct kvm_sregs kvm_sregs;
-
-		memset(&kvm_sregs, 0, sizeof kvm_sregs);
-		r = kvm_arch_vcpu_ioctl_get_sregs(vcpu, &kvm_sregs);
+		kvm_sregs = kzalloc(sizeof(struct kvm_sregs), GFP_KERNEL);
+		r = -ENOMEM;
+		if (!kvm_sregs)
+			goto out;
+		memset(kvm_sregs, 0, sizeof(struct kvm_sregs));
+		r = kvm_arch_vcpu_ioctl_get_sregs(vcpu, kvm_sregs);
 		if (r)
 			goto out;
 		r = -EFAULT;
-		if (copy_to_user(argp, &kvm_sregs, sizeof kvm_sregs))
+		if (copy_to_user(argp, kvm_sregs, sizeof(struct kvm_sregs)))
 			goto out;
 		r = 0;
 		break;
 	}
 	case KVM_SET_SREGS: {
-		struct kvm_sregs kvm_sregs;
-
+		kvm_sregs = kmalloc(sizeof(struct kvm_sregs), GFP_KERNEL);
+		r = -ENOMEM;
+		if (!kvm_sregs)
+			goto out;
 		r = -EFAULT;
-		if (copy_from_user(&kvm_sregs, argp, sizeof kvm_sregs))
+		if (copy_from_user(kvm_sregs, argp, sizeof(struct kvm_sregs)))
 			goto out;
-		r = kvm_arch_vcpu_ioctl_set_sregs(vcpu, &kvm_sregs);
+		r = kvm_arch_vcpu_ioctl_set_sregs(vcpu, kvm_sregs);
 		if (r)
 			goto out;
 		r = 0;
@@ -1051,25 +1058,28 @@ out_free2:
 		break;
 	}
 	case KVM_GET_FPU: {
-		struct kvm_fpu fpu;
-
-		memset(&fpu, 0, sizeof fpu);
-		r = kvm_arch_vcpu_ioctl_get_fpu(vcpu, &fpu);
+		fpu = kzalloc(sizeof(struct kvm_fpu), GFP_KERNEL);
+		r = -ENOMEM;
+		if (!fpu)
+			goto out;
+		r = kvm_arch_vcpu_ioctl_get_fpu(vcpu, fpu);
 		if (r)
 			goto out;
 		r = -EFAULT;
-		if (copy_to_user(argp, &fpu, sizeof fpu))
+		if (copy_to_user(argp, fpu, sizeof(struct kvm_fpu)))
 			goto out;
 		r = 0;
 		break;
 	}
 	case KVM_SET_FPU: {
-		struct kvm_fpu fpu;
-
+		fpu = kmalloc(sizeof(struct kvm_fpu), GFP_KERNEL);
+		r = -ENOMEM;
+		if (!fpu)
+			goto out;
 		r = -EFAULT;
-		if (copy_from_user(&fpu, argp, sizeof fpu))
+		if (copy_from_user(fpu, argp, sizeof(struct kvm_fpu)))
 			goto out;
-		r = kvm_arch_vcpu_ioctl_set_fpu(vcpu, &fpu);
+		r = kvm_arch_vcpu_ioctl_set_fpu(vcpu, fpu);
 		if (r)
 			goto out;
 		r = 0;
@@ -1079,6 +1089,8 @@ out_free2:
 		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
 	}
 out:
+	kfree(fpu);
+	kfree(kvm_sregs);
 	return r;
 }
 


-- Dave