Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sat, 27 Jan 2018 08:42:43 -0500
From:   Konrad Rzeszutek Wilk <konrad@darnok.org>
To:     "Hansen, Dave" <dave.hansen@intel.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Andi Kleen <ak@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Liran Alon <liran.alon@oracle.com>,
        Laura Abbott <labbott@redhat.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Borislav Petkov <bp@suse.de>,
        "Mallick, Asit K" <asit.k.mallick@intel.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        Peter Anvin <hpa@zytor.com>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        KVM list <kvm@vger.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation
Message-ID: <20180127134239.GA25029@localhost.localdomain>
References: <7c0b0879-3448-43e4-8380-4708fc787113@default>
 <50c5d627-8975-184b-b50f-4cc02c5816c5@intel.com>
 <1516957886.30244.161.camel@infradead.org>
 <CA+55aFxRsAh_dv6aoDNj+yqzcgzctda0ETZ_2DbjMwSZDwPLDA@mail.gmail.com>
 <20180126175901.GL26209@tassilo.jf.intel.com>
 <20180126190257.GS14668@char.us.oracle.com>
 <0089A7AA75120F4087B2E7CB6BF3E53442A9AA0A@CRSMSX104.amr.corp.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <0089A7AA75120F4087B2E7CB6BF3E53442A9AA0A@CRSMSX104.amr.corp.intel.com>
User-Agent: Mutt/1.9.1 (2017-09-22)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Jan 26, 2018 at 07:11:47PM +0000, Hansen, Dave wrote:
> The need for RSB stuffing in all the various scenarios and what the heck it actually mitigates is freakishly complicated.  I've tried to write it all down in one place: https://goo.gl/pXbvBE

Thank you for sharing that.

One question on the third from the top (' RSB Stuff (16) After
irq/nmi/#PF/...').

It says that :"Return from interrupt path (more than 16 deep) can empty
RSB".

Just to clarify - you mean all the returns ('ret') that are happening after
we call do_IRQ and the stack unwinds - but before we do an 'iret' correct?

I am 99% sure that is what you mean, but just confirming as one could read
this as: 'Need to do RSB after an iret' (say you are in the kernel
and then get an interrupt and iret back to kernel).