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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 6C3ACC433DB for ; Fri, 29 Jan 2021 23:41:38 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D72AC64DEC for ; Fri, 29 Jan 2021 23:41:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D72AC64DEC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=tklengyel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.78595.143040 (Exim 4.92) (envelope-from ) id 1l5dOG-0006yY-Ix; Fri, 29 Jan 2021 23:41:24 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 78595.143040; Fri, 29 Jan 2021 23:41:24 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l5dOG-0006yR-Ft; Fri, 29 Jan 2021 23:41:24 +0000 Received: by outflank-mailman (input) for mailman id 78595; Fri, 29 Jan 2021 23:41:23 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l5dOF-0006yK-0i for xen-devel@lists.xenproject.org; Fri, 29 Jan 2021 23:41:23 +0000 Received: from MTA-11-4.privateemail.com (unknown [198.54.127.104]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id a861946b-7267-404f-9927-d1eb37f45718; Fri, 29 Jan 2021 23:41:21 +0000 (UTC) Received: from mta-11.privateemail.com (localhost [127.0.0.1]) by mta-11.privateemail.com (Postfix) with ESMTP id 714FF80055 for ; Fri, 29 Jan 2021 18:41:20 -0500 (EST) Received: from mail-wr1-f54.google.com (unknown [10.20.151.200]) by mta-11.privateemail.com (Postfix) with ESMTPA id 382EC80041 for ; Fri, 29 Jan 2021 23:41:20 +0000 (UTC) Received: by mail-wr1-f54.google.com with SMTP id a1so10480885wrq.6 for ; Fri, 29 Jan 2021 15:41:20 -0800 (PST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: a861946b-7267-404f-9927-d1eb37f45718 X-Gm-Message-State: AOAM530AArng4EUoxmp5Oizp/IEiB2J4wSM36ZTDxiJPzECLE6z3bB6S tli/eHGJRQKvTNrqZf4oD8JpcxHDXh/bHdCqx8k= X-Google-Smtp-Source: ABdhPJx2tAkXktf+VBJ96ylPg6R6r4hbFDpCSeQf85uJiXMVejemCgbHxw7ULFi3fJG1WkSupiu8G8U1NsK0/C8OJ4w= X-Received: by 2002:adf:f687:: with SMTP id v7mr6956605wrp.182.1611963678770; Fri, 29 Jan 2021 15:41:18 -0800 (PST) MIME-Version: 1.0 References: <20210121212718.2441-1-andrew.cooper3@citrix.com> <20210121212718.2441-11-andrew.cooper3@citrix.com> <0a34175c-9bc1-9449-413b-01d743d201fc@citrix.com> In-Reply-To: <0a34175c-9bc1-9449-413b-01d743d201fc@citrix.com> From: Tamas K Lengyel Date: Fri, 29 Jan 2021 18:40:42 -0500 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v7 10/10] x86/vm_event: Carry Processor Trace buffer offset in vm_event To: Andrew Cooper Cc: Jan Beulich , Tamas K Lengyel , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Wei Liu , Jun Nakajima , Kevin Tian , =?UTF-8?B?TWljaGHFgiBMZXN6Y3p5xYRza2k=?= , Xen-devel Content-Type: text/plain; charset="UTF-8" X-Virus-Scanned: ClamAV using ClamSMTP On Fri, Jan 29, 2021 at 6:22 PM Andrew Cooper wrote: > > On 26/01/2021 14:27, Jan Beulich wrote: > > On 21.01.2021 22:27, Andrew Cooper wrote: > >> --- a/xen/arch/x86/vm_event.c > >> +++ b/xen/arch/x86/vm_event.c > >> @@ -251,6 +251,9 @@ void vm_event_fill_regs(vm_event_request_t *req) > >> > >> req->data.regs.x86.shadow_gs = ctxt.shadow_gs; > >> req->data.regs.x86.dr6 = ctxt.dr6; > >> + > >> + if ( hvm_vmtrace_output_position(curr, &req->data.regs.x86.pt_offset) != 1 ) > >> + req->data.regs.x86.pt_offset = ~0; > > Ah. (Regarding my earlier question about this returning -errno or > > boolean). > > > >> --- a/xen/include/public/vm_event.h > >> +++ b/xen/include/public/vm_event.h > >> @@ -223,6 +223,12 @@ struct vm_event_regs_x86 { > >> */ > >> uint64_t npt_base; > >> > >> + /* > >> + * Current offset in the Processor Trace buffer. For Intel Processor Trace > >> + * this is MSR_RTIT_OUTPUT_MASK. Set to ~0 if no Processor Trace is active. > >> + */ > >> + uint64_t pt_offset; > > According to vmtrace_output_position() the value is only one half > > of what the named MSR contains. Perhaps "... this is from MSR_..."? > > Not sure whether, despite this, there still is a reason to have > > this 64-bit wide. > > This is a vestigial remnant which escaped the "use vmtrace uniformly" work. > > It should match the domctl_vmtrace_output_position() format, so each > interface gives the same content for the attempted-platform-neutral version. >From the vm_event ABI perspective it's simpler to have a 64-bit value here even if the max value it may possibly carry is never going to use the whole 64-bit width. I rather not play with shortening it just to add padding somewhere else. As for what it's called is not that important from my perspective, vmtrace_pos or something like that for example is fine by me. Tamas