From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225KS8pvTkSrMnpanghWkIxPw4wH8YNXOD44RVUqoHHTYTUpsEopz085RC6JkkVaK9WbWFWf ARC-Seal: i=1; a=rsa-sha256; t=1517409884; cv=none; d=google.com; s=arc-20160816; b=XwlPWtnznwFUAHwiiQOSvWOMMQ7BwS2UHvhoQWrMOp2cEorvSUGcZKXO2+BAMmcV6i 5n58OALpSGDamFsRAy5RzUJj81CxieXjE36BYfkkejMHrBFxZ90QSiG8QXSB769F1rBN 8OybL7xH+32vyLJzw1C8NM6LDNBxNKWMZpWpAQIFuWGBb3y3KyZwVEOxMaBVh+AdsAaL GcdBK7BAKCAqtgPpDksTqfa9BVWlC/ZFGVc4MVBnyCwTE4kqG98V+Mh5CEgBR08TK5dO Tokdnqiie0OiDNJcZFUy6ZIe5tdCufaYg0psInhyJsDINhDXujt2b1lCqE1rE3KIF6/R K6xw== 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=eDmXylBdwwI0dlJZp8AJMAwigveEqzOVCu90tYrpPCk=; b=ajJEzGX+c+TPFoCr5Q7HmxLz/cKjoASVi2wTWTmmwA/29mK6W31ltqzI/OrExHd7vj GdC3lIlulxD2VB+oSU5yxZEcW6OXGRqWSQiHzxbI3gOG5kPDX1LEPuuFaqbb/A5KPU1B 4OrXZalkJnNBmz/f+RQVgl5aDpmVgQIiI2ZVN3UFh732B3rsFibzSMDargvoo8Mw/A44 0kVMLu+EPqtyC0VPzTkHoyqmvSrBWzGwOOWkti8zkmVd9g/g2Y3xawb0EmpMPItJFAr0 RNp7/Yv6A/qYIpVjMkPxnO/pNmrxr5c2J65IKfd4GHEHbbfPbok2jb8qDxIILzuKpInr h+Eg== 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: Wed, 31 Jan 2018 12:44:41 -0200 From: Eduardo Habkost To: "Dr. David Alan Gilbert" Cc: Borislav Petkov , Thomas Gleixner , Christophe de Dinechin , Alan Cox , Linus Torvalds , David Woodhouse , Arjan van de Ven , KarimAllah Ahmed , Linux Kernel Mailing List , Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Ashok Raj , Asit Mallick , 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 , Radim =?utf-8?B?S3LEjW3DocWZ?= , Tim Chen , Tom Lendacky , KVM list , the arch/x86 maintainers Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support infrastructure Message-ID: <20180131144441.GK26425@localhost.localdomain> References: <1517259759.18619.38.camel@infradead.org> <20180130204623.583b1a7a@alans-desktop> <200C59E8-80F3-4FEC-BA3B-E6A56FA12C74@dinechin.org> <20180131110406.GB2521@work-vm> <20180131115211.2cxz2xj6elv37p6t@pd.tnic> <20180131123036.GD2521@work-vm> <20180131131834.jzown5pteqzd3xmg@pd.tnic> <20180131140449.GF2521@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180131140449.GF2521@work-vm> 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?1591119586821416565?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Jan 31, 2018 at 02:04:49PM +0000, Dr. David Alan Gilbert wrote: > * Borislav Petkov (bp@suse.de) wrote: > > On Wed, Jan 31, 2018 at 12:30:36PM +0000, Dr. David Alan Gilbert wrote: > > > Indeed, it's only for this weird case where you suddenly need to change > > > it. > > > > No, there's more: > > > > .name = "Broadwell-noTSX", > > .name = "Haswell-noTSX", > > Haswell came out and we made the CPU definition, and then got a > microcode update that removed the feature. > > So the common feature of noTSX and IBRS is that they're the only two > cases where a CPU has released and then the flags have changed later. Also, if anybody don't like it, users can already specify, e.g., "Broadwell,-hle,-rtm" or "Skylake,+spec_ctrl". QEMU only adds have the -noTSX and -IBRS CPU for convenience of management systems that don't know how to check/configure individual CPU features. We're working with libvirt and OpenStack folks to make this kind of trick unnecessary. -- Eduardo