From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs Date: Tue, 13 Feb 2018 11:55:52 +0100 Message-ID: References: <1518449255-2182-1-git-send-email-dwmw@amazon.co.uk> <1518449255-2182-2-git-send-email-dwmw@amazon.co.uk> <7e2e5ad1-49b6-1fdb-4a62-8ad6aefc30a0@redhat.com> <1518509708.12890.33.camel@infradead.org> <27c85759-e662-d281-f8a0-0a80ca8ee18f@redhat.com> <1518517262.12890.43.camel@infradead.org> <1518518198.12890.48.camel@infradead.org> <02bd3fdd-1b73-6cab-fb09-38ba933396bd@redhat.com> <1518519234.12890.58.camel@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit To: David Woodhouse , tglx@linutronix.de, x86@kernel.org, kvm@vger.kernel.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, arjan.van.de.ven@intel.com, dave.hansen@intel.com Return-path: In-Reply-To: <1518519234.12890.58.camel@infradead.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 13/02/2018 11:53, David Woodhouse wrote: >> You have my vote. :)  Really, IBRS_ALL makes no sense and it would be >> nice to know _why_ Intel is pushing something that makes no sense. > No, IBRS_ALL *does* make sense. It's not a complete fix, but it's as > much of a fix as they should shoe-horn into the generation of CPUs > which are currently going to the fabs. > > With IBRS_ALL they presumably add tags to the predictions with the VMX > mode and ring, to give complete protection against predictions being > used in a more privileged mode. Yeah, but I still don't get why they need an MSR to turn those tags on. Is it basically a chicken bit in the wrong direction? Paolo