commit 10589a4699bb978c781ce73bbae8ca942c5250c9
author Marcelo Tosatti <mtosatti@redhat.com> Thu Dec 20 19:18:22 2007 -0500
committer Avi Kivity <avi@qumranet.com> Wed Jan 30 18:01:20 2008 +0200
tree 5585ed87fff0a2ba259fcc6f998022481da75f68
parent 774ead3ad9bcbc05ef6aaebb9bdf8b4c3126923b

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>

virt/kvm/kvm_main.c

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 @@
  *
  * 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 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 @@
 /*
  * 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 @@
 	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 @@
 
 	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;