From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753494AbcCLPgZ (ORCPT ); Sat, 12 Mar 2016 10:36:25 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:34374 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752720AbcCLPgT (ORCPT ); Sat, 12 Mar 2016 10:36:19 -0500 Date: Sat, 12 Mar 2016 16:36:15 +0100 From: Ingo Molnar To: Andy Lutomirski Cc: X86 ML , Paolo Bonzini , Peter Zijlstra , KVM list , Arjan van de Ven , xen-devel , "linux-kernel@vger.kernel.org" , Linus Torvalds , Andrew Morton Subject: Re: [PATCH v3 2/5] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops Message-ID: <20160312153615.GB17873@gmail.com> References: <35f2f107e0d85473a0e66c08f93d571a9c72b7fc.1457723023.git.luto@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35f2f107e0d85473a0e66c08f93d571a9c72b7fc.1457723023.git.luto@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andy Lutomirski wrote: > This demotes an OOPS and likely panic due to a failed non-"safe" MSR > access to a WARN and, for RDMSR, a return value of zero. If > panic_on_oops is set, then failed unsafe MSR accesses will still > oops and panic. > > To be clear, this type of failure should *not* happen. This patch > exists to minimize the chance of nasty undebuggable failures due on > systems that used to work due to a now-fixed CONFIG_PARAVIRT=y bug. > > Signed-off-by: Andy Lutomirski > --- > arch/x86/include/asm/msr.h | 10 ++++++++-- > arch/x86/mm/extable.c | 33 +++++++++++++++++++++++++++++++++ > 2 files changed, 41 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h > index 93fb7c1cffda..1487054a1a70 100644 > --- a/arch/x86/include/asm/msr.h > +++ b/arch/x86/include/asm/msr.h > @@ -92,7 +92,10 @@ static inline unsigned long long native_read_msr(unsigned int msr) > { > DECLARE_ARGS(val, low, high); > > - asm volatile("rdmsr" : EAX_EDX_RET(val, low, high) : "c" (msr)); > + asm volatile("1: rdmsr\n" > + "2:\n" > + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_rdmsr_unsafe) > + : EAX_EDX_RET(val, low, high) : "c" (msr)); > if (msr_tracepoint_active(__tracepoint_read_msr)) > do_trace_read_msr(msr, EAX_EDX_VAL(val, low, high), 0); > return EAX_EDX_VAL(val, low, high); > @@ -119,7 +122,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr, > static inline void native_write_msr(unsigned int msr, > unsigned low, unsigned high) > { > - asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory"); > + asm volatile("1: wrmsr\n" > + "2:\n" > + _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe) > + : : "c" (msr), "a"(low), "d" (high) : "memory"); > if (msr_tracepoint_active(__tracepoint_read_msr)) > do_trace_write_msr(msr, ((u64)high << 32 | low), 0); > } > diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c > index 9dd7e4b7fcde..f310714e6e6d 100644 > --- a/arch/x86/mm/extable.c > +++ b/arch/x86/mm/extable.c > @@ -49,6 +49,39 @@ bool ex_handler_ext(const struct exception_table_entry *fixup, > } > EXPORT_SYMBOL(ex_handler_ext); > > +bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup, > + struct pt_regs *regs, int trapnr) > +{ > + WARN(1, "unsafe MSR access error: RDMSR from 0x%x", > + (unsigned int)regs->cx); Btw., instead of the safe/unsafe naming (which has an emotional and security secondary attribute), shouldn't we move this over to a _check() (or _checking()) naming instead that we do in other places in the kernel? I.e.: rdmsr(msr, l, h); and: if (rdmsr_check(msr, l, h)) { ... } and then we could name the helpers as _check() and _nocheck() - which is neutral naming. Thanks, Ingo