From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755875AbcBBQTt (ORCPT ); Tue, 2 Feb 2016 11:19:49 -0500 Received: from foss.arm.com ([217.140.101.70]:56708 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755486AbcBBQTr (ORCPT ); Tue, 2 Feb 2016 11:19:47 -0500 Subject: Re: [PATCH v2 10/21] arm64: KVM: VHE: Split save/restore of sysregs shared between EL1 and EL2 To: Christoffer Dall References: <1453737235-16522-1-git-send-email-marc.zyngier@arm.com> <1453737235-16522-11-git-send-email-marc.zyngier@arm.com> <20160201135438.GL1478@cbox> <56B07ADD.60300@arm.com> <20160202154645.GE6190@cbox> Cc: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu From: Marc Zyngier X-Enigmail-Draft-Status: N1110 Organization: ARM Ltd Message-ID: <56B0D720.9000901@arm.com> Date: Tue, 2 Feb 2016 16:19:44 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0 MIME-Version: 1.0 In-Reply-To: <20160202154645.GE6190@cbox> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/02/16 15:46, Christoffer Dall wrote: > On Tue, Feb 02, 2016 at 09:46:05AM +0000, Marc Zyngier wrote: >> On 01/02/16 13:54, Christoffer Dall wrote: >>> On Mon, Jan 25, 2016 at 03:53:44PM +0000, Marc Zyngier wrote: >>>> A handful of system registers are still shared between EL1 and EL2, >>>> even while using VHE. These are tpidr*_el[01], actlr_el1, sp0, elr, >>>> and spsr. >>> >>> So by shared registers you mean registers that do both have an EL0/1 >>> version as well as an EL2 version, but where accesses aren't rewritten >>> transparently? >> >> No, I mean that these registers do *not* have a separate banked version. >> There is only a single set of registers, which have to be save/restored >> the old way. > > huh, ARMv8 clearly specifies the existence of TPIDR_EL0, TPIDR_EL1, and > TPIDR_EL2, for example. > > I cannot seem to find anywhere in the VHE spec that says that the > TPIDR_EL2 goes away. I'm confused now. Nothing goes away, but these registers do not get renamed either. For example, TPIDR_EL1 doesn't magically access TPIDR_EL2 when running at EL2+VHE, and there is no TPIDR_EL12 accessor either. So TPIDR_EL1 is effectively "shared" between host and guest, and must be save/restored (note that the host kernel still uses TIPDR_EL1 even when running with VHE, and that KVM still uses TPIDR_EL2 to cache the current vcpu). >> >>> >>> also, by sp0 do you mean sp_el0, and by elr you mean elr_el1, and by >>> spsr you mean spsr_el1 ? >> >> sp0 -> sp_el0 indeed. elr and spsr really are the guest PC and PSTATE, >> so I should really reword this commit message, it is utterly confusing. >> > I guess I don't understand the definition of a 'shared' register given > your comments here... Does this make it clearer? Thanks, M. -- Jazz is not dead. It just smells funny...