From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_MED,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA8CFECDFAA for ; Fri, 13 Jul 2018 01:22:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C4AE208E9 for ; Fri, 13 Jul 2018 01:22:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="NZ28Z36e" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C4AE208E9 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387951AbeGMBee (ORCPT ); Thu, 12 Jul 2018 21:34:34 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:45612 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387892AbeGMBed (ORCPT ); Thu, 12 Jul 2018 21:34:33 -0400 Received: by mail-pf0-f194.google.com with SMTP id i26-v6so10198767pfo.12 for ; Thu, 12 Jul 2018 18:22:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=u8A8CIn8JEixzzWHTcYRFM2KmjqUKk+LyvlpcjdAiFA=; b=NZ28Z36eOBDrbDf75CvuIH7wl5ACqxGC5qbN1LPXXuM2OPn1vf7mL2ytd/+GioM83g csFvaqlsn8n0Q4lb/vYyI2R4Q/uZrdhEKCiGZLWxMdVOUfLKLgrCwVXOC+8yjtpaPjhx NY+x7e5KqvDnHPfdVxMiiz1LdweQKZGon+9W+lFdNYsHGMWJD4A9MYixG1fC3oGLd4uv X8KGg+1bQrCo9EnzIyjZF7FhEf91CX2c1ybXawAeIj/mdR16BxhEp2hMPqb3Is9dqUTQ lKGtuTGzaToc9TAeP5VqxmQ1K/0Kme7WvZLgOSbiNgliIOfJSFE2KHrbiChFRsdszbJr UmbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=u8A8CIn8JEixzzWHTcYRFM2KmjqUKk+LyvlpcjdAiFA=; b=HqUpuRDzarcIvsWTsyjYCgjx0zK6BtStxyQ2aH58hl4CUx594j4tv4BYWVwZVECz4D nm0yEmOaBS8NsmXjZ2Pchtids9AGDG3+Az/v5z9X45nl/XKC0oUQwBF6gEHB8NrMYq4L VYqZ/7box6WR97jTPonkUdzmZX5dzlzz4w7XqVYqyMJiNTmrpAn8PryBa1Bbxp0SnZxu xAXrfgZbvT/Xn1ykxp4xPuMlWGuFFlMU82ZstE8ANhfjvv9xgU8gaFCV8tmueb8vetpU AjPA000kTLjtsmKRv2Yhc6kUWlQHDgiX/i807kPI1MX0XRFNsS6vUnHGrViGAl9c9K55 Xf0A== X-Gm-Message-State: AOUpUlFbVgge7Mlknmvk3YE/Chr8EN/qBel6+SKs8iDnlzpQLQ+RKEVu cl8FF5pevP0Fik+EyKhU3ToSAg== X-Google-Smtp-Source: AAOMgpebUI6iWlzxfgtvV5BhszhUhBzpSO8S2PEFzqQ+xb0gG5qrHNKzjdlSvz13jGYfUZwPrIUD2w== X-Received: by 2002:a62:464f:: with SMTP id t76-v6mr4806764pfa.118.1531444941751; Thu, 12 Jul 2018 18:22:21 -0700 (PDT) Received: from [100.112.85.58] ([104.133.9.106]) by smtp.gmail.com with ESMTPSA id g20-v6sm37952872pfo.94.2018.07.12.18.22.20 (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 12 Jul 2018 18:22:20 -0700 (PDT) Date: Thu, 12 Jul 2018 18:22:13 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: "Metzger, Markus T" cc: Hugh Dickins , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , "Shishkin, Alexander" , "Kleen, Andi" , Dave Hansen , Thomas Gleixner , Stephane Eranian , Linux Kernel Mailing List Subject: Re: [bug] kpti, perf_event, bts: sporadic truncated trace In-Reply-To: Message-ID: References: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 12 Jul 2018, Metzger, Markus T wrote: > Hello, > > Starting with 4.15 I noticed that BTS is sporadically missing the tail > of the trace in the perf_event data buffer. It shows as > > [decode error (1): instruction overflow] > > in GDB. Chances to see this are higher the longer the debuggee is > running. With this [1] tiny patch to one of GDB's tests, I am able to > reproduce it reliably on my box. To run the test, use: > > $ make -s check RUNTESTFLAGS="gdb.btrace/exception.exp" > > from the gdb/ sub-directory in the GDB build directory. > > The issue remains when I use 'nopti' on the kernel command-line. > > > Bisecting yielded commit > > c1961a4 x86/events/intel/ds: Map debug buffers in cpu_entry_area > > I reverted the commit on top of v4.17 [2] and the issue disappears > when I use 'nopti' on the kernel command-line. > > regards, > markus. > > > [1] > diff --git a/gdb/testsuite/gdb.btrace/exception.exp b/gdb/testsuite/gdb.btrace/exception.exp > index 9408d61..a24ddd3 100755 > --- a/gdb/testsuite/gdb.btrace/exception.exp > +++ b/gdb/testsuite/gdb.btrace/exception.exp > @@ -36,16 +36,12 @@ if ![runto_main] { > gdb_test_no_output "set record function-call-history-size 0" > > # set bp > -set bp_1 [gdb_get_line_number "bp.1" $srcfile] > set bp_2 [gdb_get_line_number "bp.2" $srcfile] > -gdb_breakpoint $bp_1 > gdb_breakpoint $bp_2 > > -# trace the code between the two breakpoints > -gdb_continue_to_breakpoint "cont to bp.1" ".*$srcfile:$bp_1\r\n.*" > # increase the BTS buffer size - the trace can be quite big > -gdb_test_no_output "set record btrace bts buffer-size 128000" > -gdb_test_no_output "record btrace" > +gdb_test_no_output "set record btrace bts buffer-size 1024000" > +gdb_test_no_output "record btrace bts" > gdb_continue_to_breakpoint "cont to bp.2" ".*$srcfile:$bp_2\r\n.*" > > # show the flat branch trace > > > [2] > diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c [ snipped the revert ] Although my name was kept on that commit as a generous courtesy, it did change a lot after leaving my fingers - and I was never the best person to be making perf changes in the first place! I'm sorry to hear that it's breaking you, I've spent a little while looking through its final state, most of it looks fine to me, but I notice one discrepancy: whose effect I cannot predict at all, but there's a chance that it has something to do with what you're seeing. A little "optimization" crept into alloc_bts_buffer() along the way, which now places bts_interrupt_threshold not on a record boundary. And Stephane has shown me the sentence in Vol 3B, 17.4.9, which says "This address must point to an offset from the BTS buffer base that is a multiple of the BTS record size." Please give the patch below a try, and let us know if it helps (if it does not, then I think we'll need perfier expertise than I can give). Hugh --- 4.18-rc4/arch/x86/events/intel/ds.c 2018-06-03 14:15:21.000000000 -0700 +++ linux/arch/x86/events/intel/ds.c 2018-07-12 17:38:28.471378616 -0700 @@ -408,9 +408,11 @@ static int alloc_bts_buffer(int cpu) ds->bts_buffer_base = (unsigned long) cea; ds_update_cea(cea, buffer, BTS_BUFFER_SIZE, PAGE_KERNEL); ds->bts_index = ds->bts_buffer_base; - max = BTS_RECORD_SIZE * (BTS_BUFFER_SIZE / BTS_RECORD_SIZE); - ds->bts_absolute_maximum = ds->bts_buffer_base + max; - ds->bts_interrupt_threshold = ds->bts_absolute_maximum - (max / 16); + max = BTS_BUFFER_SIZE / BTS_RECORD_SIZE; + ds->bts_absolute_maximum = ds->bts_buffer_base + + max * BTS_RECORD_SIZE; + ds->bts_interrupt_threshold = ds->bts_absolute_maximum - + (max / 16) * BTS_RECORD_SIZE; return 0; }