linux-kernel - [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

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Message-Id: <195642a5e9fd4515ad8ca4cd8bcffd4900df5790.1405437568.git.luto@amacapital.net>
Date:	Tue, 15 Jul 2014 08:26:41 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	boris.ostrovsky@...cle.com, linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andy Lutomirski <luto@...capital.net>, stable@...r.kernel.org
Subject: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

Xen doesn't call start_secondary.

Cc: stable@...r.kernel.org
Signed-off-by: Andy Lutomirski <luto@...capital.net>
---

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.

 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)
 
 	xen_setup_cpu_clockevents();
 
+	/*
+	 * Enable the espfix hack for this CPU
+	 */
+#ifdef CONFIG_X86_ESPFIX64
+	init_espfix_ap();
+#endif
+
 	notify_cpu_starting(cpu);
 
 	set_cpu_online(cpu, true);
-- 
1.9.3

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