From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:39634 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752134AbdLFRZq (ORCPT ); Wed, 6 Dec 2017 12:25:46 -0500 Date: Wed, 6 Dec 2017 17:25:51 +0000 From: Will Deacon To: Julien Thierry Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, Christoffer Dall , Marc Zyngier , Catalin Marinas , stable@vger.kernel.org Subject: Re: [PATCH] arm64: kvm: Prevent restoring stale PMSCR_EL1 for vcpu Message-ID: <20171206172551.GD25408@arm.com> References: <1512580189-5921-1-git-send-email-julien.thierry@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1512580189-5921-1-git-send-email-julien.thierry@arm.com> Sender: stable-owner@vger.kernel.org List-ID: On Wed, Dec 06, 2017 at 05:09:49PM +0000, Julien Thierry wrote: > When VHE is not present, KVM needs to save and restores PMSCR_EL1 when > possible. If SPE is used by the host, value of PMSCR_EL1 cannot be saved > for the guest. > If the host starts using SPE between two save+restore on the same vcpu, > restore will write the value of PMSCR_EL1 read during the first save. > > Make sure __debug_save_spe_nvhe clears the value of the saved PMSCR_EL1 > when the guest cannot use SPE. Ok, so the problem is that we have a stale (non-zero) saved pmscr_el1, and therefore the restore code unconditionally restores that even though SPE is no longer in use by the host. Well spotted! > Signed-off-by: Julien Thierry > Cc: Christoffer Dall > Cc: Marc Zyngier > Cc: Catalin Marinas > Cc: Will Deacon > Cc: > --- > arch/arm64/kvm/hyp/debug-sr.c | 3 +++ > 1 file changed, 3 insertions(+) Reviewed-by: Will Deacon Will