From ce29a1f8bd99aac409904b4ca4fd700e67802556 Mon Sep 17 00:00:00 2001 From: Christian Ehrhardt Date: Mon, 3 Sep 2007 20:32:38 +0200 Subject: [PATCH] [x86 setup] Work around bug in Xen HVM Apparently XEN does not keep the contents of the 48-bit gdt_48 data structure that is passed to lgdt in the XEN machine state. Instead it appears to save the _address_ of the 48-bit descriptor somewhere. Unfortunately this data happens to reside on the stack and is probably no longer availiable at the time of the actual protected mode jump. This is Xen bug but given that there is a one-line patch to work around this problem, the linux kernel should probably do this. My fix is to make the gdt_48 description in setup_gdt static (in setup_idt this is already the case). This allows the kernel to boot under Xen HVM again. Signed-off-by: Christian Ehrhardt Signed-off-by: H. Peter Anvin --- arch/i386/boot/pm.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/i386/boot/pm.c b/arch/i386/boot/pm.c index 6be9ca811d..09fb342cc6 100644 --- a/arch/i386/boot/pm.c +++ b/arch/i386/boot/pm.c @@ -122,7 +122,11 @@ static void setup_gdt(void) /* DS: data, read/write, 4 GB, base 0 */ [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff), }; - struct gdt_ptr gdt; + /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead + of the gdt_ptr contents. Thus, make it static so it will + stay in memory, at least long enough that we switch to the + proper kernel GDT. */ + static struct gdt_ptr gdt; gdt.len = sizeof(boot_gdt)-1; gdt.ptr = (u32)&boot_gdt + (ds() << 4); -- 2.20.1