commit 8a7ae055f3533b520401c170ac55e30628b34df5
author Izik Eidus <avi@qumranet.com> Thu Oct 18 11:09:33 2007 +0200
committer Avi Kivity <avi@qumranet.com> Wed Jan 30 17:52:54 2008 +0200
tree f9654746dc92fa18ef66e49e12537dc6cb1d32e6
parent cea7bb21280e3a825e64b54740edc5d3e6e4193c

KVM: MMU: Partial swapping of guest memory

This allows guest memory to be swapped.  Pages which are currently mapped
via shadow page tables are pinned into memory, but all other pages can
be freely swapped.

The patch makes gfn_to_page() elevate the page's reference count, and
introduces kvm_release_page() that pairs with it.

Signed-off-by: Izik Eidus <izike@qumranet.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm_main.c

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 47000be..f86a47c 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -300,19 +300,6 @@
 	return kvm;
 }
 
-static void kvm_free_userspace_physmem(struct kvm_memory_slot *free)
-{
-	int i;
-
-	for (i = 0; i < free->npages; ++i) {
-		if (free->phys_mem[i]) {
-			if (!PageReserved(free->phys_mem[i]))
-				SetPageDirty(free->phys_mem[i]);
-			page_cache_release(free->phys_mem[i]);
-		}
-	}
-}
-
 static void kvm_free_kernel_physmem(struct kvm_memory_slot *free)
 {
 	int i;
@@ -330,9 +317,7 @@
 {
 	if (!dont || free->phys_mem != dont->phys_mem)
 		if (free->phys_mem) {
-			if (free->user_alloc)
-				kvm_free_userspace_physmem(free);
-			else
+			if (!free->user_alloc)
 				kvm_free_kernel_physmem(free);
 			vfree(free->phys_mem);
 		}
@@ -361,7 +346,7 @@
 
 	for (i = 0; i < ARRAY_SIZE(vcpu->pio.guest_pages); ++i)
 		if (vcpu->pio.guest_pages[i]) {
-			__free_page(vcpu->pio.guest_pages[i]);
+			kvm_release_page(vcpu->pio.guest_pages[i]);
 			vcpu->pio.guest_pages[i] = NULL;
 		}
 }
@@ -752,19 +737,8 @@
 		memset(new.phys_mem, 0, npages * sizeof(struct page *));
 		memset(new.rmap, 0, npages * sizeof(*new.rmap));
 		if (user_alloc) {
-			unsigned long pages_num;
-
 			new.user_alloc = 1;
-			down_read(&current->mm->mmap_sem);
-
-			pages_num = get_user_pages(current, current->mm,
-						   mem->userspace_addr,
-						   npages, 1, 1, new.phys_mem,
-						   NULL);
-
-			up_read(&current->mm->mmap_sem);
-			if (pages_num != npages)
-				goto out_unlock;
+			new.userspace_addr = mem->userspace_addr;
 		} else {
 			for (i = 0; i < npages; ++i) {
 				new.phys_mem[i] = alloc_page(GFP_HIGHUSER
@@ -1039,12 +1013,39 @@
 
 	gfn = unalias_gfn(kvm, gfn);
 	slot = __gfn_to_memslot(kvm, gfn);
-	if (!slot)
+	if (!slot) {
+		get_page(bad_page);
 		return bad_page;
+	}
+	if (slot->user_alloc) {
+		struct page *page[1];
+		int npages;
+
+		down_read(&current->mm->mmap_sem);
+		npages = get_user_pages(current, current->mm,
+					slot->userspace_addr
+					+ (gfn - slot->base_gfn) * PAGE_SIZE, 1,
+					1, 1, page, NULL);
+		up_read(&current->mm->mmap_sem);
+		if (npages != 1) {
+			get_page(bad_page);
+			return bad_page;
+		}
+		return page[0];
+	}
+	get_page(slot->phys_mem[gfn - slot->base_gfn]);
 	return slot->phys_mem[gfn - slot->base_gfn];
 }
 EXPORT_SYMBOL_GPL(gfn_to_page);
 
+void kvm_release_page(struct page *page)
+{
+	if (!PageReserved(page))
+		SetPageDirty(page);
+	put_page(page);
+}
+EXPORT_SYMBOL_GPL(kvm_release_page);
+
 static int next_segment(unsigned long len, int offset)
 {
 	if (len > PAGE_SIZE - offset)
@@ -1060,13 +1061,16 @@
 	struct page *page;
 
 	page = gfn_to_page(kvm, gfn);
-	if (is_error_page(page))
+	if (is_error_page(page)) {
+		kvm_release_page(page);
 		return -EFAULT;
+	}
 	page_virt = kmap_atomic(page, KM_USER0);
 
 	memcpy(data, page_virt + offset, len);
 
 	kunmap_atomic(page_virt, KM_USER0);
+	kvm_release_page(page);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_read_guest_page);
@@ -1098,14 +1102,17 @@
 	struct page *page;
 
 	page = gfn_to_page(kvm, gfn);
-	if (is_error_page(page))
+	if (is_error_page(page)) {
+		kvm_release_page(page);
 		return -EFAULT;
+	}
 	page_virt = kmap_atomic(page, KM_USER0);
 
 	memcpy(page_virt + offset, data, len);
 
 	kunmap_atomic(page_virt, KM_USER0);
 	mark_page_dirty(kvm, gfn);
+	kvm_release_page(page);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_write_guest_page);
@@ -1136,13 +1143,16 @@
 	struct page *page;
 
 	page = gfn_to_page(kvm, gfn);
-	if (is_error_page(page))
+	if (is_error_page(page)) {
+		kvm_release_page(page);
 		return -EFAULT;
+	}
 	page_virt = kmap_atomic(page, KM_USER0);
 
 	memset(page_virt + offset, 0, len);
 
 	kunmap_atomic(page_virt, KM_USER0);
+	kvm_release_page(page);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_clear_guest_page);
@@ -2070,8 +2080,6 @@
 	for (i = 0; i < nr_pages; ++i) {
 		mutex_lock(&vcpu->kvm->lock);
 		page = gva_to_page(vcpu, address + i * PAGE_SIZE);
-		if (page)
-			get_page(page);
 		vcpu->pio.guest_pages[i] = page;
 		mutex_unlock(&vcpu->kvm->lock);
 		if (!page) {
@@ -3074,9 +3082,10 @@
 
 	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 	page = gfn_to_page(kvm, pgoff);
-	if (is_error_page(page))
+	if (is_error_page(page)) {
+		kvm_release_page(page);
 		return NOPAGE_SIGBUS;
-	get_page(page);
+	}
 	if (type != NULL)
 		*type = VM_FAULT_MINOR;