Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030376AbaDJSU0 (ORCPT ); Thu, 10 Apr 2014 14:20:26 -0400 Received: from smtp.citrix.com ([66.165.176.89]:48932 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030210AbaDJSUY (ORCPT ); Thu, 10 Apr 2014 14:20:24 -0400 X-IronPort-AV: E=Sophos;i="4.97,835,1389744000"; d="scan'208";a="119991015" Message-ID: <5346E0E5.606@citrix.com> Date: Thu, 10 Apr 2014 19:20:21 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Boris Ostrovsky CC: , , , , , Subject: Re: [PATCH v2] x86/xen: Fix 32-bit PV guests's usage of kernel_stack References: <1397146629-7159-1-git-send-email-boris.ostrovsky@oracle.com> In-Reply-To: <1397146629-7159-1-git-send-email-boris.ostrovsky@oracle.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/04/14 17:17, Boris Ostrovsky wrote: > Commit 198d208df4371734ac4728f69cb585c284d20a15 ("x86: Keep thread_info > on thread stack in x86_32") made 32-bit kernels use kernel_stack to point to > thread_info. That change missed a couple of updates needed by Xen's > 32-bit PV guests: > > 1. kernel_stack needs to be initialized for secondary CPUs > 2. GET_THREAD_INFO() now uses %fs register which may not be the kernel's > version when executing xen_iret(). > > With respect to the second issue, we don't need GET_THREAD_INFO() > anymore: we used it as an intermediate step to get to per_cpu xen_vcpu and avoid > referencing %fs. Now that we are going to use %fs anyway we may as well go > directly to xen_vcpu. > > Signed-off-by: Boris Ostrovsky > --- > arch/x86/xen/smp.c | 3 ++- > arch/x86/xen/xen-asm_32.S | 25 +++++++++++++++++-------- > 2 files changed, 19 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c > index a18eadd..7005974 100644 > --- a/arch/x86/xen/smp.c > +++ b/arch/x86/xen/smp.c > @@ -441,10 +441,11 @@ static int xen_cpu_up(unsigned int cpu, struct task_struct *idle) > irq_ctx_init(cpu); > #else > clear_tsk_thread_flag(idle, TIF_FORK); > +#endif > per_cpu(kernel_stack, cpu) = > (unsigned long)task_stack_page(idle) - > KERNEL_STACK_OFFSET + THREAD_SIZE; > -#endif > + > xen_setup_runstate_info(cpu); > xen_setup_timer(cpu); > xen_init_lock_cpu(cpu); > diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S > index 33ca6e4..fd92a64 100644 > --- a/arch/x86/xen/xen-asm_32.S > +++ b/arch/x86/xen/xen-asm_32.S > @@ -75,6 +75,17 @@ ENDPROC(xen_sysexit) > * stack state in whatever form its in, we keep things simple by only > * using a single register which is pushed/popped on the stack. > */ > + > +.macro POP_FS > +1: > + popw %fs > +.pushsection .fixup, "ax" > +2: movw $0, (%esp) > + jmp 1b > +.popsection > + _ASM_EXTABLE(1b,2b) > +.endm > + > ENTRY(xen_iret) > /* test eflags for special cases */ > testl $(X86_EFLAGS_VM | XEN_EFLAGS_NMI), 8(%esp) > @@ -83,15 +94,13 @@ ENTRY(xen_iret) > push %eax > ESP_OFFSET=4 # bytes pushed onto stack > > - /* > - * Store vcpu_info pointer for easy access. Do it this way to > - * avoid having to reload %fs > - */ > + /* Store vcpu_info pointer for easy access */ > #ifdef CONFIG_SMP > - GET_THREAD_INFO(%eax) > - movl %ss:TI_cpu(%eax), %eax > - movl %ss:__per_cpu_offset(,%eax,4), %eax > - mov %ss:xen_vcpu(%eax), %eax > + pushw %fs > + movl $(__KERNEL_PERCPU), %eax > + movl %eax, %fs > + movl %fs:xen_vcpu, %eax How can this get the correct per-cpu xen_vcpu pointer if it doesn't ever get the current cpu number? Doesn't this always get VCPU#0's xen_vcpu? David -- 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/