From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225+bn3X+EGwNWuzbHeGl//RGsdWKJZjOXxHd4SkJ+jMO2CJJuJKDDWH2Ps4DrdZ8Q3L242h ARC-Seal: i=1; a=rsa-sha256; t=1517320457; cv=none; d=google.com; s=arc-20160816; b=wfms/PNiqdgt9fj00syDaUast3BM31sb7Ptmhbc8/M3A/hrqXzEgqp0Nwu1o1VP+3H SeoiXIXxwoAUKir0LiU+OZzEEcmQjCs633Z9nygiJjyu4nDgxsIOJiDafjNpoHDCMo7k mKGFiDPb5l/DKSq1hFSuXGQZCUNs+SuHj7xF1QZkcvFZc26UOKqMDHY4IMp1TIylWra7 SFGzMHbqww/blKPZj+fvNqMrIrhlSGVmhu/sAO/bLWaf26DLGcOdenZ3/gdTypJjzKOO 7n/hINpjHRKMh2iFTS7wE7m+XyTs8YAgslxdBYVrQI+cWSxKhYMV4DbT7iL5TFGIxbPL TNbA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :arc-authentication-results; bh=0nxrpfpz1HsYwro92RMf0Huo8CcQhitWgViFKr5cPiI=; b=lQlB8ZfTDkQKqWoDLGwgIitTcYVHiO4obnjrxC4B1DodWWr8PKmq+C5mpQuYL+qZwG cdmlfgIwE5XM0dyCpMcofJWa/CpfN/shSXynrUQKxLWSXYCODRsEOAhRuJRNsSYYu6QJ FRPcx+BqHfbv5ZbU7t0U3XwF2ymOgve5EeZalsbTCAPTQNPAd2XUlKwKe1OMnpLvyyXy rPTY67XNm3wzd016TpUdY3+g7NZBwFmEDZZrS6IpQRK0+q8NtJ4XE+MvYwriuTBsZpPU mxnf3nskmJ7yb1N1qzU6TZT1MEokOJ2NeeZnHl3k/0G+2qlNcDwhz9sO0XnFn7xwGgBm TjyQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of arjan@linux.intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=arjan@linux.intel.com Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of arjan@linux.intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=arjan@linux.intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,435,1511856000"; d="scan'208";a="30617469" Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support infrastructure To: Linus Torvalds Cc: David Woodhouse , Eduardo Habkost , KarimAllah Ahmed , Linux Kernel Mailing List , Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Tim Chen , Tom Lendacky , KVM list , the arch/x86 maintainers , "Dr. David Alan Gilbert" References: <1516476182-5153-6-git-send-email-karahmed@amazon.de> <20180129201404.GA1588@localhost.localdomain> <1517257022.18619.30.camel@infradead.org> <20180129204256.GV25150@localhost.localdomain> <31415b7f-9c76-c102-86cd-6bf4e23e3aee@linux.intel.com> <1517259759.18619.38.camel@infradead.org> <6c024f95-b12c-9c66-91d7-208ed2c380ff@linux.intel.com> From: Arjan van de Ven Message-ID: <012d6cd1-2dc1-4130-9ac8-9e966475d120@linux.intel.com> Date: Tue, 30 Jan 2018 05:54:15 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140581449802182?= X-GMAIL-MSGID: =?utf-8?q?1591025816595742024?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 1/29/2018 7:32 PM, Linus Torvalds wrote: > On Mon, Jan 29, 2018 at 5:32 PM, Arjan van de Ven wrote: >> >> the most simple solution is that we set the internal feature bit in Linux >> to turn on the "stuff the RSB" workaround is we're on a SKL *or* as a guest >> in a VM. > > That sounds reasonable. > > However, wouldn't it be even better to extend on the current cpuid > model, and actually have some real architectural bits in there. > > Maybe it could be a bit in that IA32_ARCH_CAPABILITIES MSR. Say, add a > bit #2 that says "ret falls back on BTB". > > Then that bit basically becomes the "Skylake bit". Hmm? we can try to do that, but existing systems don't have that, and then we get in another long thread here about weird lists of stuff ;-)