diff --git a/tools/tests/x86_emulator/test_x86_emulator.c b/tools/tests/x86_emulator/test_x86_emulator.c
index 1b78bf7e45..86e298fa49 100644
--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -82,6 +82,12 @@ static int cpuid(
     return X86EMUL_OKAY;
 }
 
+#define cache_line_size() ({ \
+    unsigned int eax = 1, ebx, ecx = 0, edx; \
+    cpuid(&eax, &ebx, &ecx, &edx, NULL); \
+    edx & (1U << 19) ? (ebx >> 5) & 0x7f8 : 0; \
+})
+
 #define cpu_has_mmx ({ \
     unsigned int eax = 1, ecx = 0, edx; \
     cpuid(&eax, &ecx, &ecx, &edx, NULL); \
@@ -873,6 +879,35 @@ int main(int argc, char **argv)
 #undef set_insn
 #undef check_eip
 
+    j = cache_line_size();
+    snprintf(instr, (char *)res + MMAP_SZ - instr,
+             "Testing clzero (%u-byte line)...", j);
+    printf("%-40s", instr);
+    if ( j >= sizeof(*res) && j <= MMAP_SZ / 4 )
+    {
+        instr[0] = 0x0f; instr[1] = 0x01; instr[2] = 0xfc;
+        regs.eflags = 0x200;
+        regs.eip    = (unsigned long)&instr[0];
+        regs.eax    = (unsigned long)res + MMAP_SZ / 2 + j - 1;
+        memset((void *)res + MMAP_SZ / 4, ~0, 3 * MMAP_SZ / 4);
+        rc = x86_emulate(&ctxt, &emulops);
+        if ( (rc != X86EMUL_OKAY) ||
+             (regs.eax != (unsigned long)res + MMAP_SZ / 2 + j - 1) ||
+             (regs.eflags != 0x200) ||
+             (regs.eip != (unsigned long)&instr[3]) ||
+             (res[MMAP_SZ / 2 / sizeof(*res) - 1] != ~0U) ||
+             (res[(MMAP_SZ / 2 + j) / sizeof(*res)] != ~0U) )
+            goto fail;
+        for ( i = 0; i < j; i += sizeof(*res) )
+            if ( res[(MMAP_SZ / 2 + i) / sizeof(*res)] )
+                break;
+        if ( i < j )
+            goto fail;
+        printf("okay\n");
+    }
+    else
+        printf("skipped\n");
+
     for ( j = 1; j <= 2; j++ )
     {
 #if defined(__i386__)
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 56aef3e66a..c3672e7de6 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1069,6 +1069,7 @@ static bool_t vcpu_has(
     return rc == X86EMUL_OKAY;
 }
 
+#define vcpu_has_clflush() vcpu_has(       1, EDX, 19, ctxt, ops)
 #define vcpu_has_lzcnt() vcpu_has(0x80000001, ECX,  5, ctxt, ops)
 #define vcpu_has_bmi1()  vcpu_has(0x00000007, EBX,  3, ctxt, ops)
 
@@ -3851,6 +3852,45 @@ x86_emulate(
             if ( (rc = ops->vmfunc(ctxt) != X86EMUL_OKAY) )
                 goto done;
             goto no_writeback;
+	case 0xfc: /* clzero */ {
+            unsigned int eax = 1, ebx = 0, dummy = 0;
+            unsigned long zero = 0;
+
+            base = ad_bytes == 8 ? _regs.eax :
+                   ad_bytes == 4 ? (uint32_t)_regs.eax : (uint16_t)_regs.eax;
+            limit = 0;
+            if ( vcpu_has_clflush() &&
+                 ops->cpuid(&eax, &ebx, &dummy, &dummy, ctxt) == X86EMUL_OKAY )
+                limit = ((ebx >> 8) & 0xff) * 8;
+            generate_exception_if(limit < sizeof(long) ||
+                                  (limit & (limit - 1)), EXC_UD, -1);
+            base &= ~(limit - 1);
+            if ( override_seg == -1 )
+                override_seg = x86_seg_ds;
+            if ( ops->rep_stos )
+            {
+                unsigned long nr_reps = limit / sizeof(zero);
+
+                rc = ops->rep_stos(&zero, override_seg, base, sizeof(zero),
+                                   &nr_reps, ctxt);
+                if ( rc == X86EMUL_OKAY )
+                {
+                    base += nr_reps * sizeof(zero);
+                    limit -= nr_reps * sizeof(zero);
+                }
+                else if ( rc != X86EMUL_UNHANDLEABLE )
+                    goto done;
+            }
+            while ( limit )
+            {
+                rc = ops->write(override_seg, base, &zero, sizeof(zero), ctxt);
+                if ( rc != X86EMUL_OKAY )
+                    goto done;
+                base += sizeof(zero);
+                limit -= sizeof(zero);
+            }
+            goto no_writeback;
+        }
         }
 
         switch ( modrm_reg & 7 )