Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758715AbcCVRBA (ORCPT ); Tue, 22 Mar 2016 13:01:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:59688 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755072AbcCVRAu (ORCPT ); Tue, 22 Mar 2016 13:00:50 -0400 Date: Tue, 22 Mar 2016 18:00:47 +0100 From: Borislav Petkov To: Toshi Kani Cc: mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de, mcgrof@suse.com, jgross@suse.com, paul.gortmaker@windriver.com, konrad.wilk@oracle.com, elliott@hpe.com, x86@kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/6] x86/mtrr: Fix Xorg crashes in Qemu sessions Message-ID: <20160322170047.GD5656@pd.tnic> References: <1458175619-32206-1-git-send-email-toshi.kani@hpe.com> <1458175619-32206-2-git-send-email-toshi.kani@hpe.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1458175619-32206-2-git-send-email-toshi.kani@hpe.com> 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 Content-Length: 6036 Lines: 181 On Wed, Mar 16, 2016 at 06:46:56PM -0600, Toshi Kani wrote: > A Xorg failure on qemu32 was reported as a regression caused > by 'commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is > disabled")'. [1] This patch fixes the regression. I hope so. > Negative effects of this regression were two failures in Xorg > on qemu32 env, which were triggered by the fact that its virtual "... with QEMU CPU model "qemu32" (-cpu qemu32) ... " > CPU does not support MTRR. [2] > > #1. copy_process() failed in the check in reserve_pfn_range() > > copy_process > copy_mm > dup_mm > dup_mmap > copy_page_range > track_pfn_copy > reserve_pfn_range Here's where you describe why it failed the check and which check. > > #2. error path in copy_process() then hit WARN_ON_ONCE in > untrack_pfn(). > > x86/PAT: Xorg:509 map pfn expected mapping type uncached- > minus for [mem 0xfd000000-0xfdffffff], got write-combining > Call Trace: > dump_stack+0x58/0x79 > warn_slowpath_common+0x8b/0xc0 > ? untrack_pfn+0x9f/0xb0 > ? untrack_pfn+0x9f/0xb0 > warn_slowpath_null+0x22/0x30 > untrack_pfn+0x9f/0xb0 > ? __kunmap_atomic+0x54/0x110 > unmap_single_vma+0x56f/0x580 > ? pagevec_move_tail_fn+0xa0/0xa0 > unmap_vmas+0x43/0x60 > exit_mmap+0x5f/0xf0 > mmput+0x2d/0xa0 > copy_process.part.47+0x1229/0x1430 > _do_fork+0xb4/0x3b0 > SyS_clone+0x2c/0x30 > do_syscall_32_irqs_on+0x54/0xb0 > entry_INT80_32+0x2a/0x2a You can delete the offsets after the "+" - they're useless. > These negative effects are caused by two separate bugs, but they > can be dealt in lower priority. ?? > Fixing the pat_init() issue below > avoids Xorg to hit these cases. > > When the CPU does not support MTRR, MTRR does not call pat_init(), > which leaves PAT enabled without initializing PAT. This pat_init() > issue is a long-standing issue, but manifested as issue #1 (and then > hit issue #2) with the commit commit 9cd25aac1f44 ? > because the memtype now tracks cache > attribute with 'page_cache_mode'. A WC map request is tracked as WC > in memtype, but sets a PTE as UC (pgprot) per __cachemode2pte_tbl[]. > This caused the error in reserve_pfn_range() when it was called from > track_pfn_copy(), which obtained pgprot from a PTE. It converts > pgprot to page_cache_mode, which does not necessarily result in > the original page_cache_mode since __cachemode2pte_tbl[] redirects > multiple types to UC. This is a separate issue in reserve_pfn_range(). Good. > This pat_init() issue existed before the commit, but we used pgprot > in memtype. Hence, we did not have issue #1 before. But WC request > resulted in WT in effect because WC pgrot is actually WT when PAT > is not initialized. This is not how it was designed to work. When > PAT is set to disable properly, WC is converted to UC. The use of > WT can result in a system crash if the target range does not support > WT. Fortunately, nobody ran into such issue before. > > To fix this pat_init() issue, PAT code has been enhanced to provide > pat_disable() interface, which disables the OS to initialize PAT MSR, ... prevents the OS from initializing the PAT MSR. > and sets PAT table to the BIOS handoff state. > This patch changes > MTRR code to call pat_disable() when MTRR is disabled as PAT cannot > be initialized in this case. This sets PAT to disable properly, and > makes PAT code to bypass the memtype check. This avoids issue #1 > (which can be dealt in lower priority). You don't need all that text from "This patch ..." on - we can see that in the diff. The commit message needs to contain "why" not "what". > > [1]: https://lkml.org/lkml/2016/3/3/828 > [2]: https://lkml.org/lkml/2016/3/4/775 I believe I already mentioned that links should be supplied like this: Link: http://lkml.kernel.org/r/ > Signed-off-by: Toshi Kani > Cc: Borislav Petkov > Cc: Luis R. Rodriguez > Cc: Juergen Gross > Cc: Ingo Molnar > Cc: H. Peter Anvin > Cc: Thomas Gleixner > --- > arch/x86/include/asm/mtrr.h | 6 +++++- > arch/x86/kernel/cpu/mtrr/main.c | 10 +++++++++- > 2 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h > index b94f6f6..634c593 100644 > --- a/arch/x86/include/asm/mtrr.h > +++ b/arch/x86/include/asm/mtrr.h > @@ -24,6 +24,7 @@ > #define _ASM_X86_MTRR_H > > #include > +#include > > > /* > @@ -83,9 +84,12 @@ static inline int mtrr_trim_uncached_memory(unsigned long end_pfn) > static inline void mtrr_centaur_report_mcr(int mcr, u32 lo, u32 hi) > { > } > +static inline void mtrr_bp_init(void) > +{ > + pat_disable("Skip PAT initialization"); Make that more user-friendly: "MTRRs disabled, skipping PAT initialization too." > +} > > #define mtrr_ap_init() do {} while (0) > -#define mtrr_bp_init() do {} while (0) > #define set_mtrr_aps_delayed_init() do {} while (0) > #define mtrr_aps_init() do {} while (0) > #define mtrr_bp_restore() do {} while (0) > diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c > index 10f8d47..2d7d8d7 100644 > --- a/arch/x86/kernel/cpu/mtrr/main.c > +++ b/arch/x86/kernel/cpu/mtrr/main.c > @@ -759,8 +759,16 @@ void __init mtrr_bp_init(void) > } > } > > - if (!mtrr_enabled()) > + if (!mtrr_enabled()) { > pr_info("MTRR: Disabled\n"); > + > + /* > + * PAT initialization relies on MTRR's rendezvous handler. > + * Skip PAT init until the handler can initialize both > + * features independently. > + */ > + pat_disable("Skip PAT initialization"); Ditto: you can merge the pr_info text with the pat_disable() string. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --