Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

From: Boris Ostrovsky
Date: Tue Jul 15 2014 - 11:43:22 EST

On 07/15/2014 11:38 AM, Konrad Rzeszutek Wilk wrote:
On Tue, Jul 15, 2014 at 08:26:41AM -0700, Andy Lutomirski wrote:
Xen doesn't call start_secondary.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>

espfix still doesn't seem to work on Xen (it goes boom in some way that
I don't understand right now), but initializing all CPUs instead of just
one of them seems like a good start.

ISTM the right fix is probably to shove the espfix logic into
native_iret and to tweak the paravirt logic so that native_iret always
gets invoked. I suspect that Xen will need its own implementation of
espfix64 in the hypervisor and that, ultimately, someone may want to
stop initializing espfix64 at all on Xen guests.
I think just disallowing would be preferrable.

I've been looking at sigreturn_64 and it seems to be crashing dom0 (with both mine and your patches). In kprobe_int3_handler().


Thanks for posting this patch!
arch/x86/xen/smp.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 7005974..eea9bcc 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -23,6 +23,7 @@
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/cpu.h>
+#include <asm/espfix.h>
#include <xen/interface/xen.h>
#include <xen/interface/vcpu.h>
@@ -85,6 +86,13 @@ static void cpu_bringup(void)
+ /*
+ * Enable the espfix hack for this CPU
+ */
+#ifdef CONFIG_X86_ESPFIX64
+ init_espfix_ap();
set_cpu_online(cpu, true);

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at