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>

diff --git a/drivers/kvm/x86.c b/drivers/kvm/x86.c
index 9db4e3242b626b5c8b429add2290f9c5c59472a3..3b79684a3c0ccfeb653dc0b63817a38a9235c321 100644 (file)
--- 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);
 }