From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755225Ab3AHVIp (ORCPT ); Tue, 8 Jan 2013 16:08:45 -0500 Received: from mail.skyhub.de ([78.46.96.112]:42327 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754960Ab3AHVIn (ORCPT ); Tue, 8 Jan 2013 16:08:43 -0500 Date: Tue, 8 Jan 2013 22:08:40 +0100 From: Borislav Petkov To: "H. Peter Anvin" Cc: Konrad Rzeszutek Wilk , Yinghai Lu , Thomas Gleixner , Ingo Molnar , "Eric W. Biederman" , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 00/27] x86, boot, 64bit: Add support for loading ramdisk and bzImage above 4G Message-ID: <20130108210840.GC23616@liondog.tnic> Mail-Followup-To: Borislav Petkov , "H. Peter Anvin" , Konrad Rzeszutek Wilk , Yinghai Lu , Thomas Gleixner , Ingo Molnar , "Eric W. Biederman" , Andrew Morton , linux-kernel@vger.kernel.org References: <1355814959-10573-1-git-send-email-yinghai@kernel.org> <20121222024225.GG3468@phenom.dumpdata.com> <20121222132419.GB2936@phenom.dumpdata.com> <50D8FBF9.6050509@zytor.com> <20121225115226.GD7720@liondog.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 25, 2012 at 07:51:54AM -0800, H. Peter Anvin wrote: > Right, it's the ljmpq issue. > > Borislav Petkov wrote: > > >On Mon, Dec 24, 2012 at 05:06:01PM -0800, H. Peter Anvin wrote: > >> Could this be the ljmpq problem that Borislav reported > >> (Intel implemented ljmpq, AMD didn't, and I was tempted by a > >> micro-optimization which broke AMD which made it into the patchset)? > > > >It has to be. Just booted Yinghai's -v8 in kvm on an AMD host and it > >worked fine. > > > >With the change below it keeps rebooting like I reported earlier. I'd > >go > >out on a limb here and guess that the guest is triple-faulting due to > >an > >unhandled #GP caused by an invalid opcode or similar. > > > >--- > >diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S > >index d94f6d68be2a..1842d30c96a2 100644 > >--- a/arch/x86/kernel/head_64.S > >+++ b/arch/x86/kernel/head_64.S > >@@ -279,11 +279,8 @@ ENTRY(secondary_startup_64) > > * REX.W + FF /5 JMP m16:64 Jump far, absolute indirect, > > * address given in m16:64. > > */ > >- movq initial_code(%rip),%rax > > pushq $0 # fake return address to stop unwinder > >- pushq $__KERNEL_CS # set correct cs > >- pushq %rax # target address in negative space > >- lretq > >+ rex64 ljmp *initial_code(%rip) > > > > #ifdef CONFIG_HOTPLUG_CPU Btw, I'm being told that we could also do a JMP FAR through a call gate in 64-bit mode. Basically, the insn operand contains a CS:OFFSET whereas the OFFSET is ignored but only CS is looked at. It has to point to a call gate descriptor which contains two pieces of a Code-Segment Offset[0:63] and this points into the virtual address space where we want to jump to. Here's a picture to explain it better (figure 4-31 on page 105): http://support.amd.com/us/Processor_TechDocs/24593_APM_v2.pdf It looks like Intel should support that too, AFAICT. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --