From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752049AbdFSSCE (ORCPT ); Mon, 19 Jun 2017 14:02:04 -0400 Received: from mx2.suse.de ([195.135.220.15]:38470 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750987AbdFSSCD (ORCPT ); Mon, 19 Jun 2017 14:02:03 -0400 Date: Mon, 19 Jun 2017 20:01:47 +0200 From: Borislav Petkov To: "Luck, Tony" Cc: Dave Hansen , Naoya Horiguchi , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yazen Ghannam Subject: Re: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages Message-ID: <20170619180147.qolal6mz2wlrjbxk@pd.tnic> References: <20170616190200.6210-1-tony.luck@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170616190200.6210-1-tony.luck@intel.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (drop stable from CC) You could use git's --suppress-cc= option when sending. On Fri, Jun 16, 2017 at 12:02:00PM -0700, Luck, Tony wrote: > From: Tony Luck > > Speculative processor accesses may reference any memory that has a > valid page table entry. While a speculative access won't generate > a machine check, it will log the error in a machine check bank. That > could cause escalation of a subsequent error since the overflow bit > will be then set in the machine check bank status register. ... > @@ -1056,6 +1057,40 @@ static int do_memory_failure(struct mce *m) > return ret; > } > > +#ifdef CONFIG_X86_64 > + > +void arch_unmap_kpfn(unsigned long pfn) > +{ I guess you can move the ifdeffery inside the function. > + unsigned long decoy_addr; > + > + /* > + * Unmap this page from the kernel 1:1 mappings to make sure > + * we don't log more errors because of speculative access to > + * the page. > + * We would like to just call: > + * set_memory_np((unsigned long)pfn_to_kaddr(pfn), 1); > + * but doing that would radically increase the odds of a > + * speculative access to the posion page because we'd have > + * the virtual address of the kernel 1:1 mapping sitting > + * around in registers. > + * Instead we get tricky. We create a non-canonical address > + * that looks just like the one we want, but has bit 63 flipped. > + * This relies on set_memory_np() not checking whether we passed > + * a legal address. > + */ > + > +#if PGDIR_SHIFT + 9 < 63 /* 9 because cpp doesn't grok ilog2(PTRS_PER_PGD) */ Please no side comments. Also, explain why the build-time check. (Sign-extension going away for VA space yadda yadda..., 5 2/3 level paging :-)) Also, I'm assuming this whole "workaround" of sorts should be Intel-only? > + decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63)); > +#else > +#error "no unused virtual bit available" > +#endif > + > + if (set_memory_np(decoy_addr, 1)) > + pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn); WARNING: unnecessary whitespace before a quoted newline #107: FILE: arch/x86/kernel/cpu/mcheck/mce.c:1089: + pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn); -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) -- From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 3932C6B0279 for ; Mon, 19 Jun 2017 14:02:04 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id h64so12658827wmg.0 for ; Mon, 19 Jun 2017 11:02:04 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p34si300737wrc.158.2017.06.19.11.02.02 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 19 Jun 2017 11:02:02 -0700 (PDT) Date: Mon, 19 Jun 2017 20:01:47 +0200 From: Borislav Petkov Subject: Re: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages Message-ID: <20170619180147.qolal6mz2wlrjbxk@pd.tnic> References: <20170616190200.6210-1-tony.luck@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170616190200.6210-1-tony.luck@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Luck, Tony" Cc: Dave Hansen , Naoya Horiguchi , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yazen Ghannam (drop stable from CC) You could use git's --suppress-cc= option when sending. On Fri, Jun 16, 2017 at 12:02:00PM -0700, Luck, Tony wrote: > From: Tony Luck > > Speculative processor accesses may reference any memory that has a > valid page table entry. While a speculative access won't generate > a machine check, it will log the error in a machine check bank. That > could cause escalation of a subsequent error since the overflow bit > will be then set in the machine check bank status register. ... > @@ -1056,6 +1057,40 @@ static int do_memory_failure(struct mce *m) > return ret; > } > > +#ifdef CONFIG_X86_64 > + > +void arch_unmap_kpfn(unsigned long pfn) > +{ I guess you can move the ifdeffery inside the function. > + unsigned long decoy_addr; > + > + /* > + * Unmap this page from the kernel 1:1 mappings to make sure > + * we don't log more errors because of speculative access to > + * the page. > + * We would like to just call: > + * set_memory_np((unsigned long)pfn_to_kaddr(pfn), 1); > + * but doing that would radically increase the odds of a > + * speculative access to the posion page because we'd have > + * the virtual address of the kernel 1:1 mapping sitting > + * around in registers. > + * Instead we get tricky. We create a non-canonical address > + * that looks just like the one we want, but has bit 63 flipped. > + * This relies on set_memory_np() not checking whether we passed > + * a legal address. > + */ > + > +#if PGDIR_SHIFT + 9 < 63 /* 9 because cpp doesn't grok ilog2(PTRS_PER_PGD) */ Please no side comments. Also, explain why the build-time check. (Sign-extension going away for VA space yadda yadda..., 5 2/3 level paging :-)) Also, I'm assuming this whole "workaround" of sorts should be Intel-only? > + decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63)); > +#else > +#error "no unused virtual bit available" > +#endif > + > + if (set_memory_np(decoy_addr, 1)) > + pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn); WARNING: unnecessary whitespace before a quoted newline #107: FILE: arch/x86/kernel/cpu/mcheck/mce.c:1089: + pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn); -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix ImendA?rffer, Jane Smithard, Graham Norton, HRB 21284 (AG NA 1/4 rnberg) -- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org