KVM: MMU: Don't assume struct page for x86

This patch introduces a gfn_to_pfn() function and corresponding functions like
kvm_release_pfn_dirty().  Using these new functions, we can modify the x86
MMU to no longer assume that it can always get a struct page for any given gfn.

We don't want to eliminate gfn_to_page() entirely because a number of places
assume they can do gfn_to_page() and then kmap() the results.  When we support
IO memory, gfn_to_page() will fail for IO pages although gfn_to_pfn() will
succeed.

This does not implement support for avoiding reference counting for reserved
RAM or for IO memory.  However, it should make those things pretty straight
forward.

Since we're only introducing new common symbols, I don't think it will break
the non-x86 architectures but I haven't tested those.  I've tested Intel,
AMD, NPT, and hugetlbfs with Windows and Linux guests.

[avi: fix overflow when shifting left pfns by adding casts]

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 61 insertions, 7 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 93ed78b015c..6a52c084e06 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -40,6 +40,7 @@
 #include <linux/kvm_para.h>
 #include <linux/pagemap.h>
 #include <linux/mman.h>
+#include <linux/swap.h>
 
 #include <asm/processor.h>
 #include <asm/io.h>
@@ -458,6 +459,12 @@ int is_error_page(struct page *page)
 }
 EXPORT_SYMBOL_GPL(is_error_page);
 
+int is_error_pfn(pfn_t pfn)
+{
+	return pfn == bad_pfn;
+}
+EXPORT_SYMBOL_GPL(is_error_pfn);
+
 static inline unsigned long bad_hva(void)
 {
 	return PAGE_OFFSET;
@@ -519,7 +526,7 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 /*
  * Requires current->mm->mmap_sem to be held
  */
-struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
+pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
 {
 	struct page *page[1];
 	unsigned long addr;
@@ -530,7 +537,7 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 	addr = gfn_to_hva(kvm, gfn);
 	if (kvm_is_error_hva(addr)) {
 		get_page(bad_page);
-		return bad_page;
+		return page_to_pfn(bad_page);
 	}
 
 	npages = get_user_pages(current, current->mm, addr, 1, 1, 1, page,
@@ -538,27 +545,71 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 
 	if (npages != 1) {
 		get_page(bad_page);
-		return bad_page;
+		return page_to_pfn(bad_page);
 	}
 
-	return page[0];
+	return page_to_pfn(page[0]);
+}
+
+EXPORT_SYMBOL_GPL(gfn_to_pfn);
+
+struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
+{
+	return pfn_to_page(gfn_to_pfn(kvm, gfn));
 }
 
 EXPORT_SYMBOL_GPL(gfn_to_page);
 
 void kvm_release_page_clean(struct page *page)
 {
-	put_page(page);
+	kvm_release_pfn_clean(page_to_pfn(page));
 }
 EXPORT_SYMBOL_GPL(kvm_release_page_clean);
 
+void kvm_release_pfn_clean(pfn_t pfn)
+{
+	put_page(pfn_to_page(pfn));
+}
+EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);
+
 void kvm_release_page_dirty(struct page *page)
 {
+	kvm_release_pfn_dirty(page_to_pfn(page));
+}
+EXPORT_SYMBOL_GPL(kvm_release_page_dirty);
+
+void kvm_release_pfn_dirty(pfn_t pfn)
+{
+	kvm_set_pfn_dirty(pfn);
+	kvm_release_pfn_clean(pfn);
+}
+EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);
+
+void kvm_set_page_dirty(struct page *page)
+{
+	kvm_set_pfn_dirty(page_to_pfn(page));
+}
+EXPORT_SYMBOL_GPL(kvm_set_page_dirty);
+
+void kvm_set_pfn_dirty(pfn_t pfn)
+{
+	struct page *page = pfn_to_page(pfn);
 	if (!PageReserved(page))
 		SetPageDirty(page);
-	put_page(page);
 }
-EXPORT_SYMBOL_GPL(kvm_release_page_dirty);
+EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
+
+void kvm_set_pfn_accessed(pfn_t pfn)
+{
+	mark_page_accessed(pfn_to_page(pfn));
+}
+EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
+
+void kvm_get_pfn(pfn_t pfn)
+{
+	get_page(pfn_to_page(pfn));
+}
+EXPORT_SYMBOL_GPL(kvm_get_pfn);
 
 static int next_segment(unsigned long len, int offset)
 {
@@ -1351,6 +1402,7 @@ static struct sys_device kvm_sysdev = {
 };
 
 struct page *bad_page;
+pfn_t bad_pfn;
 
 static inline
 struct kvm_vcpu *preempt_notifier_to_vcpu(struct preempt_notifier *pn)
@@ -1392,6 +1444,8 @@ int kvm_init(void *opaque, unsigned int vcpu_size,
 		goto out;
 	}
 
+	bad_pfn = page_to_pfn(bad_page);
+
 	r = kvm_arch_hardware_setup();
 	if (r < 0)
 		goto out_free_0;