[PATCH 06/41] KVM: Use a shared page for kernel/user communication when runing a vcpu

Avi Kivity
2007-04-01T14:35:03Z

Instead of passing a 'struct kvm_run' back and forth between the kernel and
userspace, allocate a page and allow the user to mmap() it. This reduces
needless copying and makes the interface expandable by providing lots of
free space.

Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
---
drivers/kvm/kvm.h | 1 +
drivers/kvm/kvm_main.c | 54 +++++++++++++++++++++++++++++++++++------------
include/linux/kvm.h | 6 ++--
3 files changed, 44 insertions(+), 17 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 0d122bf..901b8d9 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -228,6 +228,7 @@ struct kvm_vcpu {
struct mutex mutex;
int cpu;
int launched;
+ struct kvm_run *run;
int interrupt_window_open;
unsigned long irq_summary; /* bit vector: 1 per word in irq_pending */
#define NR_IRQ_WORDS KVM_IRQ_BITMAP_SIZE(unsigned long)
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 946ed86..42be8a8 100755
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -355,6 +355,8 @@ static void kvm_free_vcpu(struct kvm_vcpu *vcpu)
kvm_mmu_destroy(vcpu);
vcpu_put(vcpu);
kvm_arch_ops->vcpu_free(vcpu);
+ free_page((unsigned long)vcpu->run);
+ vcpu->run = NULL;
}

static void kvm_free_vcpus(struct kvm *kvm)
@@ -1887,6 +1889,33 @@ static int kvm_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
return r;
}

+static struct page *kvm_vcpu_nopage(struct vm_area_struct *vma,
+ unsigned long address,
+ int *type)
+{
+ struct kvm_vcpu *vcpu = vma->vm_file->private_data;
+ unsigned long pgoff;
+ struct page *page;
+
+ *type = VM_FAULT_MINOR;
+ pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
+ if (pgoff != 0)
+ return NOPAGE_SIGBUS;
+ page = virt_to_page(vcpu->run);
+ get_page(page);
+ return page;
+}
+
+static struct vm_operations_struct kvm_vcpu_vm_ops = {
+ .nopage = kvm_vcpu_nopage,
+};
+
+static int kvm_vcpu_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ vma->vm_ops = &kvm_vcpu_vm_ops;
+ return 0;
+}
+
static int kvm_vcpu_release(struct inode *inode, struct file *filp)
{
struct kvm_vcpu *vcpu = filp->private_data;
@@ -1899,6 +1928,7 @@ static struct file_operations kvm_vcpu_fops = {
.release = kvm_vcpu_release,
.unlocked_ioctl = kvm_vcpu_ioctl,
.compat_ioctl = kvm_vcpu_ioctl,
+ .mmap = kvm_vcpu_mmap,
};

/*
@@ -1947,6 +1977,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
{
int r;
struct kvm_vcpu *vcpu;
+ struct page *page;

r = -EINVAL;
if (!valid_vcpu(n))
@@ -1961,6 +1992,12 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
return -EEXIST;
}

+ page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ r = -ENOMEM;
+ if (!page)
+ goto out_unlock;
+ vcpu->run = page_address(page);
+
vcpu->host_fx_image = (char*)ALIGN((hva_t)vcpu->fx_buf,
FX_IMAGE_ALIGN);
vcpu->guest_fx_image = vcpu->host_fx_image + FX_IMAGE_SIZE;
@@ -1990,6 +2027,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)

out_free_vcpus:
kvm_free_vcpu(vcpu);
+out_unlock:
mutex_unlock(&vcpu->mutex);
out:
return r;
@@ -2003,21 +2041,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
int r = -EINVAL;

switch (ioctl) {
- case KVM_RUN: {
- struct kvm_run kvm_run;
-
- r = -EFAULT;
- if (copy_from_user(&kvm_run, argp, sizeof kvm_run))
- goto out;
- r = kvm_vcpu_ioctl_run(vcpu, &kvm_run);
- if (r < 0 && r != -EINTR)
- goto out;
- if (copy_to_user(argp, &kvm_run, sizeof kvm_run)) {
- r = -EFAULT;
- goto out;
- }
+ case KVM_RUN:
+ r = kvm_vcpu_ioctl_run(vcpu, vcpu->run);
break;
- }
case KVM_GET_REGS: {
struct kvm_regs kvm_regs;

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 275354f..d88e750 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -11,7 +11,7 @@
#include <asm/types.h>
#include <linux/ioctl.h>

-#define KVM_API_VERSION 4
+#define KVM_API_VERSION 5

/*
* Architectural interrupt line count, and the size of the bitmap needed
@@ -49,7 +49,7 @@ enum kvm_exit_reason {
KVM_EXIT_SHUTDOWN = 8,
};

-/* for KVM_RUN */
+/* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
struct kvm_run {
/* in */
__u32 emulated; /* skip current instruction */
@@ -233,7 +233,7 @@ struct kvm_dirty_log {
/*
* ioctls for vcpu fds
*/
-#define KVM_RUN _IOWR(KVMIO, 2, struct kvm_run)
+#define KVM_RUN _IO(KVMIO, 16)
#define KVM_GET_REGS _IOR(KVMIO, 3, struct kvm_regs)
#define KVM_SET_REGS _IOW(KVMIO, 4, struct kvm_regs)
#define KVM_GET_SREGS _IOR(KVMIO, 5, struct kvm_sregs)