From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754205AbdIHFH1 (ORCPT ); Fri, 8 Sep 2017 01:07:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:45858 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753132AbdIHFHC (ORCPT ); Fri, 8 Sep 2017 01:07:02 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 511C422A72 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org From: Andy Lutomirski To: X86 ML Cc: Borislav Petkov , "linux-kernel@vger.kernel.org" , Linus Torvalds , Jiri Kosina , Andy Lutomirski Subject: [PATCH 1/2] x86/mm: Get rid of VM_BUG_ON in switch_tlb_irqs_off() Date: Thu, 7 Sep 2017 22:06:57 -0700 Message-Id: <3b4e06bbb382ca54a93218407c93925ff5871546.1504847163.git.luto@kernel.org> X-Mailer: git-send-email 2.13.5 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we hit the VM_BUG_ON(), we're detecting a genuinely bad situation, but we're very unlikely to get a useful call trace. Make it a warning instead. Signed-off-by: Andy Lutomirski --- arch/x86/mm/tlb.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index dbbcfd59726a..f4e471dd1526 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -121,8 +121,28 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * hypothetical buggy code that directly switches to swapper_pg_dir * without going through leave_mm() / switch_mm_irqs_off() or that * does something like write_cr3(read_cr3_pa()). + * + * Only do this check if CONFIG_DEBUG_VM=y because __read_cr3() + * isn't free. */ - VM_BUG_ON(__read_cr3() != (__sme_pa(real_prev->pgd) | prev_asid)); +#ifdef CONFIG_DEBUG_VM + if (WARN_ON_ONCE(__read_cr3() != + (__sme_pa(real_prev->pgd) | prev_asid))) { + /* + * If we were to BUG here, we'd be very likely to kill + * the system so hard that we don't see the call trace. + * Try to recover instead by ignoring the error and doing + * a global flush to minimize the change of corruption. + * + * (This is far from being a fully correct recovery. + * Architecturally, the CPU could prefetch something + * back into an incorrect ASID slot and leave it there + * to cause trouble down the road. It's better than + * nothing, though.) + */ + __flush_tlb_all(); + } +#endif if (real_prev == next) { VM_BUG_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) != -- 2.13.5