x86, 64-bit: swapgs pvop with a user-stack can never be called
It's never safe to call a swapgs pvop when the user stack is current -
it must be inline replaced. Rather than making a call, the
SWAPGS_UNSAFE_STACK pvop always just puts "swapgs" as a placeholder,
which must either be replaced inline or trap'n'emulated (somehow).
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/irqflags.h b/include/asm-x86/irqflags.h
index ea9bd26..d17e1f6 100644
--- a/include/asm-x86/irqflags.h
+++ b/include/asm-x86/irqflags.h
@@ -111,6 +111,7 @@
#define DISABLE_INTERRUPTS(x) cli
#ifdef CONFIG_X86_64
+#define SWAPGS_UNSAFE_STACK swapgs
#define INTERRUPT_RETURN iretq
#define USERGS_SYSRET64 \
swapgs; \
@@ -185,7 +186,6 @@
* Either way, this is a good way to document that we don't
* have a reliable stack. x86_64 only.
*/
-#define SWAPGS_UNSAFE_STACK swapgs
#define ARCH_TRACE_IRQS_ON call trace_hardirqs_on_thunk
#define ARCH_TRACE_IRQS_OFF call trace_hardirqs_off_thunk
#define ARCH_LOCKDEP_SYS_EXIT call lockdep_sys_exit_thunk