Messages in this thread Patch in this message | | | Date | Wed, 05 Sep 2007 02:39:54 +0100 | From | "H. Peter Anvin" <> | Subject | Re: [GIT PULL] x86 setup: work around bug in Xen HVM |
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Christoph Hellwig wrote: > On Tue, Sep 04, 2007 at 09:55:45AM -0700, H. Peter Anvin wrote: >> >> 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. > >> - struct gdt_ptr gdt; >> + static struct gdt_ptr gdt; > > It might make sense to add your above commit message to the code as a comment.
Good point; I have amended the commit with a brief comment:
diff --git a/arch/i386/boot/pm.c b/arch/i386/boot/pm.c index 6be9ca8..09fb342 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); -hpa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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