Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751491AbdIKLVB (ORCPT ); Mon, 11 Sep 2017 07:21:01 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:58042 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751079AbdIKLVA (ORCPT ); Mon, 11 Sep 2017 07:21:00 -0400 Subject: Re: [PATCH] arm64: KVM: Skip PSTATE.PAN reest at EL2 in non-VHE To: Dongjiu Geng , christoffer.dall@linaro.org, marc.zyngier@arm.com, james.morse@arm.com References: <1505128612-13819-1-git-send-email-gengdongjiu@huawei.com> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org From: Vladimir Murzin Message-ID: <652c020f-172f-f022-d23e-3b53375c6aae@arm.com> Date: Mon, 11 Sep 2017 12:20:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <1505128612-13819-1-git-send-email-gengdongjiu@huawei.com> 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 Content-Length: 1852 Lines: 47 On 11/09/17 12:16, Dongjiu Geng wrote: > PSTATE.PAN disables reading and/or writing to a userspace virtual > address from EL1 in non-VHE or from EL2 in VHE. In non-VHE, there is > no any userspace mapping at EL2, so no need to reest the PSTATE.PAN. ^^^^^ reset > > Signed-off-by: Dongjiu Geng > Signed-off-by: Haibin Zhang > --- > arch/arm64/kvm/hyp/entry.S | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index 12ee62d6d410..86a7549b1b4c 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -96,8 +96,12 @@ ENTRY(__guest_exit) > > add x1, x1, #VCPU_CONTEXT > > - ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > + b 2f // skip PAN at EL2 in non-VHE > +alternative_else_nop_endif > > + ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > +2: > // Store the guest regs x2 and x3 > stp x2, x3, [x1, #CPU_XREG_OFFSET(2)] > > Ok. Probably I need to say why original patch did not consider non-VHE case: - VHE and PAN features come within the same v8.1 extension bundle, so it is unlucky to see IRL implementation with PAN but no VHE. - Given above the only case where extra PAN instruction could count is VHE-enabled system with CONFIG_ARM64_VHE is not set; However, IMO, usecase for such setup is kind of debugging; it is quite obvious that those who care of performance should not disable VHE in the first place... Nit: In general it is not polite to keep posting patches in a middle of the merge window - people are busy with more important stuff... Cheers Vladimir