KVM: MMU: Make setting shadow ptes atomic on i386

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

drivers/kvm/Kconfig

@@ -11,6 +11,7 @@ if VIRTUALIZATION
 config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
 	depends on X86 && EXPERIMENTAL
+	depends on X86_CMPXCHG64 || 64BIT
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent

drivers/kvm/mmu.c

@@ -22,6 +22,7 @@
 #include <linux/mm.h>
 #include <linux/highmem.h>
 #include <linux/module.h>
+#include <asm/cmpxchg.h>
 
 #include "vmx.h"
 #include "kvm.h"
@@ -204,6 +205,15 @@ static int is_rmap_pte(u64 pte)
 		== (PT_WRITABLE_MASK | PT_PRESENT_MASK);
 }
 
+static void set_shadow_pte(u64 *sptep, u64 spte)
+{
+#ifdef CONFIG_X86_64
+	set_64bit((unsigned long *)sptep, spte);
+#else
+	set_64bit((unsigned long long *)sptep, spte);
+#endif
+}
+
 static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
 				  struct kmem_cache *base_cache, int min,
 				  gfp_t gfp_flags)
@@ -446,7 +456,7 @@ static void rmap_write_protect(struct kvm_vcpu *vcpu, u64 gfn)
 		rmap_printk("rmap_write_protect: spte %p %llx\n", spte, *spte);
 		rmap_remove(vcpu, spte);
 		kvm_arch_ops->tlb_flush(vcpu);
-		*spte &= ~(u64)PT_WRITABLE_MASK;
+		set_shadow_pte(spte, *spte & ~PT_WRITABLE_MASK);
 	}
 }
 
@@ -699,7 +709,7 @@ static void kvm_mmu_zap_page(struct kvm_vcpu *vcpu,
 		}
 		BUG_ON(!parent_pte);
 		kvm_mmu_put_page(vcpu, page, parent_pte);
-		*parent_pte = 0;
+		set_shadow_pte(parent_pte, 0);
 	}
 	kvm_mmu_page_unlink_children(vcpu, page);
 	if (!page->root_count) {

drivers/kvm/paging_tmpl.h

@@ -234,7 +234,7 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
 		spte |= gaddr;
 		spte |= PT_SHADOW_IO_MARK;
 		spte &= ~PT_PRESENT_MASK;
-		*shadow_pte = spte;
+		set_shadow_pte(shadow_pte, spte);
 		return;
 	}
 
@@ -280,7 +280,7 @@ unshadowed:
 	if (access_bits & PT_WRITABLE_MASK)
 		mark_page_dirty(vcpu->kvm, gaddr >> PAGE_SHIFT);
 
-	*shadow_pte = spte;
+	set_shadow_pte(shadow_pte, spte);
 	page_header_update_slot(vcpu->kvm, shadow_pte, gaddr);
 	if (!was_rmapped)
 		rmap_add(vcpu, shadow_pte);