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>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 2ad14fbdcfa..5d7af4bde59 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -425,6 +425,8 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
         if (!is_rmap_pte(*spte))
                 return;
         page = page_header(__pa(spte));
+        kvm_release_page(pfn_to_page((*spte & PT64_BASE_ADDR_MASK) >>
+                         PAGE_SHIFT));
         rmapp = gfn_to_rmap(kvm, page->gfns[spte - page->spt]);
         if (!*rmapp) {
                 printk(KERN_ERR "rmap_remove: %p %llx 0->BUG\n", spte, *spte);
@@ -911,6 +913,8 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)
                                                                 PT_USER_MASK;
                         if (!was_rmapped)
                                 rmap_add(vcpu, &table[index], v >> PAGE_SHIFT);
+                        else
+                                kvm_release_page(pfn_to_page(p >> PAGE_SHIFT));
                         return 0;
                 }
 
@@ -925,6 +929,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)
                                                      1, 3, &table[index]);
                         if (!new_table) {
                                 pgprintk("nonpaging_map: ENOMEM\n");
+                                kvm_release_page(pfn_to_page(p >> PAGE_SHIFT));
                                 return -ENOMEM;
                         }
 
@@ -1039,8 +1044,11 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
 
         paddr = gpa_to_hpa(vcpu->kvm, addr & PT64_BASE_ADDR_MASK);
 
-        if (is_error_hpa(paddr))
+        if (is_error_hpa(paddr)) {
+                kvm_release_page(pfn_to_page((paddr & PT64_BASE_ADDR_MASK)
+                                 >> PAGE_SHIFT));
                 return 1;
+        }
 
         return nonpaging_map(vcpu, addr & PAGE_MASK, paddr);
 }
@@ -1507,6 +1515,7 @@ static void audit_mappings_page(struct kvm_vcpu *vcpu, u64 page_pte,
                 } else {
                         gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, va);
                         hpa_t hpa = gpa_to_hpa(vcpu, gpa);
+                        struct page *page;
 
                         if (is_shadow_present_pte(ent)
                             && (ent & PT64_BASE_ADDR_MASK) != hpa)
@@ -1519,6 +1528,9 @@ static void audit_mappings_page(struct kvm_vcpu *vcpu, u64 page_pte,
                                  && !is_error_hpa(hpa))
                                 printk(KERN_ERR "audit: (%s) notrap shadow,"
                                        " valid guest gva %lx\n", audit_msg, va);
+                        page = pfn_to_page((gpa & PT64_BASE_ADDR_MASK)
+                                           >> PAGE_SHIFT);
+                        kvm_release_page(page);
 
                 }
         }