From: Keir Fraser <keir.fraser@citrix.com>
Date: Thu, 2 Jul 2009 15:16:15 +0000 (+0100)
Subject: kexec: switch to a known good/static GDT before kexec
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~13656
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=4cb90ae29a9c8615d7087773362062545f052d0f;p=xen.git

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@citrix.com>
---

diff --git a/xen/arch/x86/machine_kexec.c b/xen/arch/x86/machine_kexec.c
index 7488834593..f44aba2b5b 100644
--- a/xen/arch/x86/machine_kexec.c
+++ b/xen/arch/x86/machine_kexec.c
@@ -113,6 +113,18 @@ void machine_reboot_kexec(xen_kexec_image_t *image)
 
 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) )
     {