[Xen-changelog] [xen-3.4-testing] kexec: switch to a known good/static GDT before kexec

["Xen patchbot-3.4-testing" <patchbot-3.4-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1246547832 -3600
# Node ID ddf8e5917a12027af82adc599469ac59da1635e2
# Parent  82b0f51763777b4039b2c0889f1b139059dcdb39
kexec: switch to a known good/static GDT before kexec

kexec has been failing (at least on 32on64, didn't try others) since
18771:8e18dd41c6c7 "x86: reduce GDT switching". Ensure that we are
using a known good GDT before attempting to switch to compatability
mode.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
xen-unstable changeset:   19885:863ae334467c
xen-unstable date:        Thu Jul 02 16:16:15 2009 +0100
---
 xen/arch/x86/machine_kexec.c |   12 ++++++++++++
 1 files changed, 12 insertions(+)

diff -r 82b0f5176377 -r ddf8e5917a12 xen/arch/x86/machine_kexec.c
--- a/xen/arch/x86/machine_kexec.c      Thu Jul 02 11:38:18 2009 +0100
+++ b/xen/arch/x86/machine_kexec.c      Thu Jul 02 16:17:12 2009 +0100
@@ -115,6 +115,18 @@ void machine_reboot_kexec(xen_kexec_imag
 
 void machine_kexec(xen_kexec_image_t *image)
 {
+    struct desc_ptr gdt_desc = {
+        .base = (unsigned long)(boot_cpu_gdt_table - FIRST_RESERVED_GDT_ENTRY),
+        .limit = LAST_RESERVED_GDT_BYTE
+    };
+
+    /*
+     * compat_machine_kexec() returns to idle pagetables, which requires us
+     * to be running on a static GDT mapping (idle pagetables have no GDT
+     * mappings in their per-domain mapping area).
+     */
+    asm volatile ( "lgdt %0" : : "m" (gdt_desc) );
+
 #ifdef CONFIG_COMPAT
     if ( is_pv_32on64_domain(dom0) )
     {

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