4 files changed, 13 insertions, 7 deletions

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3eb572ed3d7a..0870825a9568 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -308,8 +308,9 @@ sysenter_past_esp:
 
         movl    %esp, %eax
         call    do_fast_syscall_32
-        testl   %eax, %eax
-        jz      .Lsyscall_32_done
+        /* XEN PV guests always use IRET path */
+        ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+                    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
 
 /* Opportunistic SYSEXIT */
         TRACE_IRQS_ON                   /* User mode traces as IRQs on. */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c3201830a85e..402e34a21559 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -121,8 +121,9 @@ sysenter_flags_fixed:
 
         movq    %rsp, %rdi
         call    do_fast_syscall_32
-        testl   %eax, %eax
-        jz      .Lsyscall_32_done
+        /* XEN PV guests always use IRET path */
+        ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+                    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
         jmp     sysret32_from_system_call
 
 sysenter_fix_flags:
@@ -200,8 +201,9 @@ ENTRY(entry_SYSCALL_compat)
 
         movq    %rsp, %rdi
         call    do_fast_syscall_32
-        testl   %eax, %eax
-        jz      .Lsyscall_32_done
+        /* XEN PV guests always use IRET path */
+        ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+                    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
 
         /* Opportunistic SYSRET */
 sysret32_from_system_call:
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index e4f8010f22e0..f7ba9fbf12ee 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -216,6 +216,7 @@
 #define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
 #define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
 #define X86_FEATURE_VMMCALL     ( 8*32+15) /* Prefer vmmcall to vmcall */
+#define X86_FEATURE_XENPV       ( 8*32+16) /* "" Xen paravirtual guest */
 
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5774800ff583..d315151411e5 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
 static void xen_set_cpu_features(struct cpuinfo_x86 *c)
 {
-        if (xen_pv_domain())
+        if (xen_pv_domain()) {
                 clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+                set_cpu_cap(c, X86_FEATURE_XENPV);
+        }
 }
 
 const struct hypervisor_x86 x86_hyper_xen = {