From http://xenbits.xen.org/linux-2.6.18-xen.hg (tip 1182:7b36058ce050)
Subject: xen3 arch-x86_64
From: xen-devel@lists.xen.org
Patch-mainline: n/a
Acked-by: jbeulich@suse.com

--- head.orig/arch/x86/kernel/asm-offsets_64.c	2012-04-10 14:24:22.000000000 +0200
+++ head/arch/x86/kernel/asm-offsets_64.c	2012-04-10 15:46:12.000000000 +0200
@@ -76,8 +76,10 @@ int main(void)
 	BLANK();
 #undef ENTRY
 
+#ifndef CONFIG_X86_NO_TSS
 	OFFSET(TSS_ist, tss_struct, x86_tss.ist);
 	BLANK();
+#endif
 
 	DEFINE(__NR_syscall_max, sizeof(syscalls_64) - 1);
 	DEFINE(NR_syscalls, sizeof(syscalls_64));
--- head.orig/arch/x86/kernel/machine_kexec_64.c	2010-04-15 09:38:56.000000000 +0200
+++ head/arch/x86/kernel/machine_kexec_64.c	2010-04-15 09:44:51.000000000 +0200
@@ -21,6 +21,119 @@
 #include <asm/mmu_context.h>
 #include <asm/debugreg.h>
 
+#ifdef CONFIG_XEN
+
+/* In the case of Xen, override hypervisor functions to be able to create
+ * a regular identity mapping page table...
+ */
+
+#include <xen/interface/kexec.h>
+#include <xen/interface/memory.h>
+
+#define x__pmd(x) ((pmd_t) { (x) } )
+#define x__pud(x) ((pud_t) { (x) } )
+#define x__pgd(x) ((pgd_t) { (x) } )
+
+#define x_pmd_val(x)   ((x).pmd)
+#define x_pud_val(x)   ((x).pud)
+#define x_pgd_val(x)   ((x).pgd)
+
+static inline void x_set_pmd(pmd_t *dst, pmd_t val)
+{
+	x_pmd_val(*dst) = x_pmd_val(val);
+}
+
+static inline void x_set_pud(pud_t *dst, pud_t val)
+{
+	x_pud_val(*dst) = phys_to_machine(x_pud_val(val));
+}
+
+static inline void x_pud_clear (pud_t *pud)
+{
+	x_pud_val(*pud) = 0;
+}
+
+static inline void x_set_pgd(pgd_t *dst, pgd_t val)
+{
+	x_pgd_val(*dst) = phys_to_machine(x_pgd_val(val));
+}
+
+static inline void x_pgd_clear (pgd_t * pgd)
+{
+	x_pgd_val(*pgd) = 0;
+}
+
+#define X__PAGE_KERNEL_LARGE_EXEC \
+         _PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_PSE
+#define X_KERNPG_TABLE _PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY
+
+#define __ma(x) (pfn_to_mfn(__pa((x)) >> PAGE_SHIFT) << PAGE_SHIFT)
+
+#if PAGES_NR > KEXEC_XEN_NO_PAGES
+#error PAGES_NR is greater than KEXEC_XEN_NO_PAGES - Xen support will break
+#endif
+
+#if PA_CONTROL_PAGE != 0
+#error PA_CONTROL_PAGE is non zero - Xen support will break
+#endif
+
+void machine_kexec_setup_load_arg(xen_kexec_image_t *xki, struct kimage *image)
+{
+	void *control_page;
+	void *table_page;
+
+	memset(xki->page_list, 0, sizeof(xki->page_list));
+
+	control_page = page_address(image->control_code_page) + PAGE_SIZE;
+	memcpy(control_page, relocate_kernel, PAGE_SIZE);
+
+	table_page = page_address(image->control_code_page);
+
+	xki->page_list[PA_CONTROL_PAGE] = __ma(control_page);
+	xki->page_list[PA_TABLE_PAGE] = __ma(table_page);
+
+	xki->page_list[PA_PGD] = __ma(kexec_pgd);
+	xki->page_list[PA_PUD_0] = __ma(kexec_pud0);
+	xki->page_list[PA_PUD_1] = __ma(kexec_pud1);
+	xki->page_list[PA_PMD_0] = __ma(kexec_pmd0);
+	xki->page_list[PA_PMD_1] = __ma(kexec_pmd1);
+	xki->page_list[PA_PTE_0] = __ma(kexec_pte0);
+	xki->page_list[PA_PTE_1] = __ma(kexec_pte1);
+}
+
+int __init machine_kexec_setup_resources(struct resource *hypervisor,
+					 struct resource *phys_cpus,
+					 int nr_phys_cpus)
+{
+	int k;
+
+	/* The per-cpu crash note resources belong to the hypervisor resource */
+	for (k = 0; k < nr_phys_cpus; k++)
+		request_resource(hypervisor, phys_cpus + k);
+
+	return 0;
+}
+
+void machine_kexec_register_resources(struct resource *res) { ; }
+
+#else /* CONFIG_XEN */
+
+#define x__pmd(x) __pmd(x)
+#define x__pud(x) __pud(x)
+#define x__pgd(x) __pgd(x)
+
+#define x_set_pmd(x, y) set_pmd(x, y)
+#define x_set_pud(x, y) set_pud(x, y)
+#define x_set_pgd(x, y) set_pgd(x, y)
+
+#define x_pud_clear(x) pud_clear(x)
+#define x_pgd_clear(x) pgd_clear(x)
+
+#define X__PAGE_KERNEL_LARGE_EXEC __PAGE_KERNEL_LARGE_EXEC
+#define X_KERNPG_TABLE _KERNPG_TABLE
+
+#endif /* CONFIG_XEN */
+
 static int init_one_level2_page(struct kimage *image, pgd_t *pgd,
 				unsigned long addr)
 {
@@ -63,7 +176,7 @@ static void init_level2_page(pmd_t *leve
 	addr &= PAGE_MASK;
 	end_addr = addr + PUD_SIZE;
 	while (addr < end_addr) {
-		set_pmd(level2p++, __pmd(addr | __PAGE_KERNEL_LARGE_EXEC));
+		x_set_pmd(level2p++, x__pmd(addr | X__PAGE_KERNEL_LARGE_EXEC));
 		addr += PMD_SIZE;
 	}
 }
@@ -88,12 +201,12 @@ static int init_level3_page(struct kimag
 		}
 		level2p = (pmd_t *)page_address(page);
 		init_level2_page(level2p, addr);
-		set_pud(level3p++, __pud(__pa(level2p) | _KERNPG_TABLE));
+		x_set_pud(level3p++, x__pud(__pa(level2p) | X_KERNPG_TABLE));
 		addr += PUD_SIZE;
 	}
 	/* clear the unused entries */
 	while (addr < end_addr) {
-		pud_clear(level3p++);
+		x_pud_clear(level3p++);
 		addr += PUD_SIZE;
 	}
 out:
@@ -123,12 +236,12 @@ static int init_level4_page(struct kimag
 		result = init_level3_page(image, level3p, addr, last_addr);
 		if (result)
 			goto out;
-		set_pgd(level4p++, __pgd(__pa(level3p) | _KERNPG_TABLE));
+		x_set_pgd(level4p++, x__pgd(__pa(level3p) | X_KERNPG_TABLE));
 		addr += PGDIR_SIZE;
 	}
 	/* clear the unused entries */
 	while (addr < end_addr) {
-		pgd_clear(level4p++);
+		x_pgd_clear(level4p++);
 		addr += PGDIR_SIZE;
 	}
 out:
@@ -189,8 +302,14 @@ static int init_pgtable(struct kimage *i
 {
 	pgd_t *level4p;
 	int result;
+	unsigned long x_max_pfn = max_pfn;
+
+#ifdef CONFIG_XEN
+	x_max_pfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
+#endif
+
 	level4p = (pgd_t *)__va(start_pgtable);
-	result = init_level4_page(image, level4p, 0, max_pfn << PAGE_SHIFT);
+	result = init_level4_page(image, level4p, 0, x_max_pfn << PAGE_SHIFT);
 	if (result)
 		return result;
 	/*
@@ -224,6 +343,7 @@ void machine_kexec_cleanup(struct kimage
 	free_transition_pgtable(image);
 }
 
+#ifndef CONFIG_XEN
 /*
  * Do not allocate memory (or fail in any way) in machine_kexec().
  * We are past the point of no return, committed to rebooting now.
@@ -283,6 +403,7 @@ void machine_kexec(struct kimage *image)
 
 	__ftrace_enabled_restore(save_ftrace_enabled);
 }
+#endif
 
 void arch_crash_save_vmcoreinfo(void)
 {