[PATCH] change init_gdt to update the gdt via write_gdt, rather than a direct write.

[PATCH] change init_gdt to update the gdt via write_gdt, rather than a direct write.

[Alex Nixon]

From: Alex Nixon <alex.nixon@citrix.com>
Date: Fri, 15 Aug 2008 11:21:56 +0100
Subject: [PATCH] change init_gdt to update the gdt via write_gdt, rather than a direct write.

By writing directly, a memory access violation can occur whilst hotplugging a CPU if the entry was previously marked read-only.

Signed-off-by: Alex Nixon <alex.nixon@citrix.com>
---
 arch/x86/kernel/smpcommon.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/smpcommon.c b/arch/x86/kernel/smpcommon.c
index 99941b3..29f8bf0 100644
--- a/arch/x86/kernel/smpcommon.c
+++ b/arch/x86/kernel/smpcommon.c
@@ -13,13 +13,13 @@ EXPORT_PER_CPU_SYMBOL(this_cpu_off);
    secondary which will soon come up. */
 __cpuinit void init_gdt(int cpu)
 {
-	struct desc_struct *gdt = get_cpu_gdt_table(cpu);
+	struct desc_struct gdt;
 
-	pack_descriptor(&gdt[GDT_ENTRY_PERCPU],
-			__per_cpu_offset[cpu], 0xFFFFF,
+	pack_descriptor(&gdt, __per_cpu_offset[cpu], 0xFFFFF,
 			0x2 | DESCTYPE_S, 0x8);
+	gdt.s = 1;
 
-	gdt[GDT_ENTRY_PERCPU].s = 1;
+	write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PERCPU, &gdt, DESCTYPE_S);
 
 	per_cpu(this_cpu_off, cpu) = __per_cpu_offset[cpu];
 	per_cpu(cpu_number, cpu) = cpu;
-- 
1.5.4.3

Re: [PATCH] change init_gdt to update the gdt via write_gdt, rather than a direct write.

[Ingo Molnar]

* Alex Nixon <alex.nixon@citrix.com> wrote:

> From: Alex Nixon <alex.nixon@citrix.com>
> Date: Fri, 15 Aug 2008 11:21:56 +0100
> Subject: [PATCH] change init_gdt to update the gdt via write_gdt, rather than a direct write.
> 
> By writing directly, a memory access violation can occur whilst 
> hotplugging a CPU if the entry was previously marked read-only.

applied to tip/x86/urgent - thanks Alex.

	Ingo