From mboxrd@z Thu Jan 1 00:00:00 1970 From: Igor Mammedov Subject: Re: [Xen-devel] Re: [PATCH v2] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context Date: Fri, 02 Sep 2011 16:01:35 +0200 Message-ID: <4E60E1BF.2020206@redhat.com> References: <4E5EB794.7050909@goop.org> <1314877615-18280-1-git-send-email-imammedo@redhat.com> <4E5FB700.1070908@goop.org> <4E60914F.7080208@redhat.com> <20110902134032.GA6064@dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110902134032.GA6064@dumpdata.com> Sender: linux-kernel-owner@vger.kernel.org To: Konrad Rzeszutek Wilk Cc: Jeremy Fitzhardinge , xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org List-Id: xen-devel@lists.xenproject.org On 09/02/2011 03:40 PM, Konrad Rzeszutek Wilk wrote: > On Fri, Sep 02, 2011 at 10:18:23AM +0200, Igor Mammedov wrote: >> On 09/01/2011 06:46 PM, Jeremy Fitzhardinge wrote: >>> On 09/01/2011 04:46 AM, Igor Mammedov wrote: >>>> If vmalloc page_fault happens inside of interrupt handler with interrupts >>>> disabled then on exit path from exception handler when there is no pending >>>> interrupts, the following code (arch/x86/xen/xen-asm_32.S:112): >>>> >>>> cmpw $0x0001, XEN_vcpu_info_pending(%eax) >>>> sete XEN_vcpu_info_mask(%eax) >>>> >>>> will enable interrupts even if they has been previously disabled according to >>>> eflags from the bounce frame (arch/x86/xen/xen-asm_32.S:99) >>>> >>>> testb $X86_EFLAGS_IF>>8, 8+1+ESP_OFFSET(%esp) >>>> setz XEN_vcpu_info_mask(%eax) >>>> >>>> Solution is in setting XEN_vcpu_info_mask only when it should be set >>>> according to >>>> cmpw $0x0001, XEN_vcpu_info_pending(%eax) >>>> but not clearing it if there isn't any pending events. >>>> >>>> Reproducer for bug is attached to RHBZ 707552 >>>> >>>> Signed-off-by: Igor Mammedov >>>> Signed-off-by: Jeremy Fitzhardinge >>> >>> One nit, this should be acked-by or reviewed-by, not signed-off-by, >>> since the patch isn't passing through my hands. >>> >>> J >> >> I'm new to this stuff, would you like me to re-post it? > > That is OK. I fixed it up in the git commit. Thanks for finding this one! You're welcome! I've learned a lot while debugging it. In particular, how to use kvm and qemu's gdbstub to debug xen and guest using gdb. -- Thanks, Igor