KVM: MMU: emulated cmpxchg8b should be atomic on i386

Emulate cmpxchg8b atomically on i386. This is required to avoid a guest
pte walker from seeing a splitted write.

[avi: make it compile]

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/kvm/x86.c b/drivers/kvm/x86.c
index 9db4e3242b6..3b79684a3c0 100644
--- a/drivers/kvm/x86.c
+++ b/drivers/kvm/x86.c
@@ -25,6 +25,7 @@
 #include <linux/vmalloc.h>
 #include <linux/module.h>
 #include <linux/mman.h>
+#include <linux/highmem.h>
 
 #include <asm/uaccess.h>
 #include <asm/msr.h>
@@ -1674,6 +1675,31 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
                 reported = 1;
                 printk(KERN_WARNING "kvm: emulating exchange as write\n");
         }
+#ifndef CONFIG_X86_64
+        /* guests cmpxchg8b have to be emulated atomically */
+        if (bytes == 8) {
+                gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
+                struct page *page;
+                char *addr;
+                u64 val;
+
+                if (gpa == UNMAPPED_GVA ||
+                   (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
+                        goto emul_write;
+
+                if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
+                        goto emul_write;
+
+                val = *(u64 *)new;
+                page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
+                addr = kmap_atomic(page, KM_USER0);
+                set_64bit((u64 *)(addr + offset_in_page(gpa)), val);
+                kunmap_atomic(addr, KM_USER0);
+                kvm_release_page_dirty(page);
+        }
+emul_write:
+#endif
+
         return emulator_write_emulated(addr, new, bytes, vcpu);
 }