KVM: MMU: Concurrent guest walkers

Do not hold kvm->lock mutex across the entire pagefault code,
only acquire it in places where it is necessary, such as mmu
hash list, active list, rmap and parent pte handling.

Allow concurrent guest walkers by switching walk_addr() to use
mmap_sem in read-mode.

And get rid of the lockless __gfn_to_page.

[avi: move kvm_mmu_pte_write() locking inside the function]
[avi: add locking for real mode]
[avi: fix cmpxchg locking]

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 5 insertions, 17 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4026d7d..678e805 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -227,7 +227,7 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
  *
  * Discontiguous memory is allowed, mostly for framebuffers.
  *
- * Must be called holding kvm->lock.
+ * Must be called holding mmap_sem for write.
  */
 int __kvm_set_memory_region(struct kvm *kvm,
 			    struct kvm_userspace_memory_region *mem,
@@ -338,9 +338,9 @@ int kvm_set_memory_region(struct kvm *kvm,
 {
 	int r;
 
-	mutex_lock(&kvm->lock);
+	down_write(&current->mm->mmap_sem);
 	r = __kvm_set_memory_region(kvm, mem, user_alloc);
-	mutex_unlock(&kvm->lock);
+	up_write(&current->mm->mmap_sem);
 	return r;
 }
 EXPORT_SYMBOL_GPL(kvm_set_memory_region);
@@ -456,7 +456,7 @@ static unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 /*
  * Requires current->mm->mmap_sem to be held
  */
-static struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn)
+struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 {
 	struct page *page[1];
 	unsigned long addr;
@@ -481,17 +481,6 @@ static struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn)
 	return page[0];
 }
 
-struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
-{
-	struct page *page;
-
-	down_read(&current->mm->mmap_sem);
-	page = __gfn_to_page(kvm, gfn);
-	up_read(&current->mm->mmap_sem);
-
-	return page;
-}
-
 EXPORT_SYMBOL_GPL(gfn_to_page);
 
 void kvm_release_page_clean(struct page *page)
@@ -977,8 +966,7 @@ static int kvm_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 
 	if (!kvm_is_visible_gfn(kvm, vmf->pgoff))
 		return VM_FAULT_SIGBUS;
-	/* current->mm->mmap_sem is already held so call lockless version */
-	page = __gfn_to_page(kvm, vmf->pgoff);
+	page = gfn_to_page(kvm, vmf->pgoff);
 	if (is_error_page(page)) {
 		kvm_release_page_clean(page);
 		return VM_FAULT_SIGBUS;