From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935774AbcCQLiL (ORCPT ); Thu, 17 Mar 2016 07:38:11 -0400 Received: from mail.skyhub.de ([78.46.96.112]:35380 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934948AbcCQLiI (ORCPT ); Thu, 17 Mar 2016 07:38:08 -0400 Date: Thu, 17 Mar 2016 12:37:40 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: linux-tip-commits@vger.kernel.org, luto@kernel.org, peterz@infradead.org, dvlasenk@redhat.com, luto@amacapital.net, brgerst@gmail.com, andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org, david.vrabel@citrix.com, JBeulich@suse.com, torvalds@linux-foundation.org, hpa@zytor.com, tglx@linutronix.de, boris.ostrovsky@oracle.com, mingo@kernel.org Subject: Re: [tip:x86/urgent] x86/iopl/64: Properly context-switch IOPL on Xen PV Message-ID: <20160317113740.GB28772@pd.tnic> References: <693c3bd7aeb4d3c27c92c622b7d0f554a458173c.1458162709.git.luto@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 17, 2016 at 02:19:12AM -0700, tip-bot for Andy Lutomirski wrote: > Commit-ID: b7a584598aea7ca73140cb87b40319944dd3393f > Gitweb: http://git.kernel.org/tip/b7a584598aea7ca73140cb87b40319944dd3393f > Author: Andy Lutomirski > AuthorDate: Wed, 16 Mar 2016 14:14:21 -0700 > Committer: Ingo Molnar > CommitDate: Thu, 17 Mar 2016 09:49:26 +0100 > > x86/iopl/64: Properly context-switch IOPL on Xen PV > > On Xen PV, regs->flags doesn't reliably reflect IOPL and the > exit-to-userspace code doesn't change IOPL. We need to context > switch it manually. > > I'm doing this without going through paravirt because this is > specific to Xen PV. After the dust settles, we can merge this with > the 32-bit code, tidy up the iopl syscall implementation, and remove > the set_iopl pvop entirely. > > Fixes XSA-171. > > Reviewewd-by: Jan Beulich > Signed-off-by: Andy Lutomirski > Cc: Andrew Cooper > Cc: Andy Lutomirski > Cc: Boris Ostrovsky > Cc: Borislav Petkov > Cc: Brian Gerst > Cc: David Vrabel > Cc: Denys Vlasenko > Cc: H. Peter Anvin > Cc: Jan Beulich > Cc: Linus Torvalds > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: stable@vger.kernel.org > Link: http://lkml.kernel.org/r/693c3bd7aeb4d3c27c92c622b7d0f554a458173c.1458162709.git.luto@kernel.org > Signed-off-by: Ingo Molnar > --- > arch/x86/include/asm/xen/hypervisor.h | 2 ++ > arch/x86/kernel/process_64.c | 12 ++++++++++++ > arch/x86/xen/enlighten.c | 2 +- > 3 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h > index 8b2d4be..39171b3 100644 > --- a/arch/x86/include/asm/xen/hypervisor.h > +++ b/arch/x86/include/asm/xen/hypervisor.h > @@ -62,4 +62,6 @@ void xen_arch_register_cpu(int num); > void xen_arch_unregister_cpu(int num); > #endif > > +extern void xen_set_iopl_mask(unsigned mask); > + > #endif /* _ASM_X86_XEN_HYPERVISOR_H */ > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c > index b9d99e0..9f75187 100644 > --- a/arch/x86/kernel/process_64.c > +++ b/arch/x86/kernel/process_64.c > @@ -48,6 +48,7 @@ > #include > #include > #include > +#include > > asmlinkage extern void ret_from_fork(void); > > @@ -411,6 +412,17 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) > task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV)) > __switch_to_xtra(prev_p, next_p, tss); > > +#ifdef CONFIG_XEN > + /* > + * On Xen PV, IOPL bits in pt_regs->flags have no effect, and > + * current_pt_regs()->flags may not match the current task's > + * intended IOPL. We need to switch it manually. > + */ > + if (unlikely(static_cpu_has(X86_FEATURE_XENPV) && > + prev->iopl != next->iopl)) > + xen_set_iopl_mask(next->iopl); > +#endif I'm wondering if it would've been cleaner if this was a arch_fixup_iopl_mask() defined in arch/x86/xen/enlighten.c and a stub otherwise. This would save you the ifdeffery and the export of xen_set_iopl_mask()... -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.