linux-kernel - Re: [PATCH v7 00/27] x86, boot, 64bit: Add support for loading ramdisk and bzImage above 4G

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Date:	Tue, 25 Dec 2012 07:51:54 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 00/27] x86, boot, 64bit: Add support for loading ramdisk and bzImage above 4G

Right, it's the ljmpq issue.

Borislav Petkov <bp@...en8.de> 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
> /*

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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