KVM: MMU: handle page removal with shadow mapping

Do not assume that a shadow mapping will always point to the same host
frame number. Fixes crash with madvise(MADV_DONTNEED).

[avi: move after first printk(), add another printk()]

Signed-off-by: Marcelo Tosatti <[e-mail]>
Signed-off-by: Avi Kivity <[e-mail]>

arch/x86/kvm/mmu.c

···
 			 int *ptwrite, gfn_t gfn, struct page *page)
 {
 	u64 spte;
-	int was_rmapped = is_rmap_pte(*shadow_pte);
+	int was_rmapped = 0;
 	int was_writeble = is_writeble_pte(*shadow_pte);
+	hfn_t host_pfn = (*shadow_pte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
 
 	pgprintk("%s: spte %llx access %x write_fault %d"
 		 " user_fault %d gfn %lx\n",
 		 __FUNCTION__, *shadow_pte, pt_access,
 		 write_fault, user_fault, gfn);
+
+	if (is_rmap_pte(*shadow_pte)) {
+		if (host_pfn != page_to_pfn(page)) {
+			pgprintk("hfn old %lx new %lx\n",
+				 host_pfn, page_to_pfn(page));
+			rmap_remove(vcpu->kvm, shadow_pte);
+		}
+		else
+			was_rmapped = 1;
+	}
 
 	/*
 	 * We don't set the accessed bit, since we sometimes want to see