From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225sXtJcFRwOXTy927WObphCWJN6ZoqDUjWvYFgUdiFAx7yqO7z/CZ4jSmvchFZFRmRlDldZ ARC-Seal: i=1; a=rsa-sha256; t=1517275818; cv=none; d=google.com; s=arc-20160816; b=0tTEyKb9//wBps0NFpwZtRhv9Ei6vaJ5gjEXHiZLKoz04m0xfDiExkEyz+icJq6Xuz s+9105pQF50xKdnSB6cOtdIPNw2sUjfPiiGHL5X22RrGDhiEv64f2Fv93E75L8zFnAeC KJBv0d5pW9/GX3m6M6FuID15nExNFRuN/6+abnP20srjhT5NrEeQbEm+gDx+uoJaDENT KnQe0DwmRI6IQ6e/1g5kfre9zqRmZZZVwxy+zDxOHLZiZ2O9FLmDdsWAVOUL/4tKFiVh iOyYyP0Oe5AJX9YYRno0T8lIYYwXVueU7FfkYp6Ei1w5d1k8LUf+Ln5ZCI2z9UJjrRQ/ fLng== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:arc-authentication-results; bh=ed7Nr/BFVHN5BTXVJ3EljH2j8wGUU2H+dxThtdndb0k=; b=Fid1W9LAo5khEi8tMrF27YWtJMYQKrfkczsnsY5uYezvXUgVZ2pcaZiSsczLDhNW7d L6vvuZlF9O7BnqZ7S8LoYgOrQuB7zQlYj4XyLkLo+GjUOIOiHWSSKGzS3TjRmhGtpGdL 03LDVHrwwsLAq91fb+p+R7G1/lANXc7Z3KM0qKUy+4A48boJqRUP5s8/m984JeR2ayHQ 6IOZLDBYPISvc5K3thkIQ/BK9/k+DaPXpp6fCu7Pp+P1ZLvG4ut5hXdkp4rS36fX9zQd dyEbwoICk5fSKlMO4t5YJV+lvyFCfUPFkpy5MAQbxz4zNmcs/f67eudv+YftT+HPMmlO y5ZA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of ehabkost@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=ehabkost@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of ehabkost@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=ehabkost@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Date: Mon, 29 Jan 2018 23:30:14 -0200 From: Eduardo Habkost To: David Dunn Cc: Jim Mattson , Andi Kleen , Arjan van de Ven , KarimAllah Ahmed , "Wilson, Matt" , "linux-kernel@vger.kernel.org" , 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 , Linus Torvalds , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Gleixner , Tim Chen , Tom Lendacky , "Jorgensen, Bryan" , "kvm@vger.kernel.org" , "x86@kernel.org" , "Dr. David Alan Gilbert" , Fred Jacobs , David Woodhouse Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support infrastructure Message-ID: <20180130013014.GE21702@localhost.localdomain> References: <7EB9643C-D2DD-477A-90DE-05DC653D2D4B@vmware.com> <20180129224124.GU26209@tassilo.jf.intel.com> <20180130011059.GB21702@localhost.localdomain> <30A89AF5-51E6-4D7F-B669-63C2B3191302@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <30A89AF5-51E6-4D7F-B669-63C2B3191302@vmware.com> X-Fnord: you can see the fnord User-Agent: Mutt/1.9.1 (2017-09-22) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140581449802182?= X-GMAIL-MSGID: =?utf-8?q?1590979009000625097?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, Jan 30, 2018 at 01:20:52AM +0000, David Dunn wrote: > Eduardo, > > This is why it would be good to have a CPUID bit that says: > "apply SkyLake RSB stuffing." That's preferable to "trust FMS" > for VMware. Agreed it would be more useful than "trust FMS". However, I believe a "no need to apply Skylake RSB stuffing" bit (which I called "we promise we won't migrate to Skylake" previously) would allow guests to enable safer behavior by default under older hypervisors that don't support this bit. > > If Intel defines such a feature flag, sets it on SkyLake, and > Linux uses it... that would be very helpful for VMware. > > I won't speak for GCE and AWS. But hopefully they can indicate > whether it would help them as well. I agree that having a standard flag on the CPUID space to specify that would be very helpful. > > If Intel cannot define/implement such a flag on SkyLake, then > maybe the engineers on this email could define a flag in the > hypervisor specific CPUID space. Linux would need to query > that flag if it sees CPUID[1].ECX[31] set. That's not as nice > since it makes detection on bare metal and virtualization > platforms different, but it better than keying off FMS. Agreed. -- Eduardo