From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Morse Subject: Re: [PATCH v4 09/21] KVM: arm/arm64: mask/unmask daif around VHE guests Date: Thu, 02 Nov 2017 12:14:28 +0000 Message-ID: <59FB0C24.7080503@arm.com> References: <20171019145807.23251-1-james.morse@arm.com> <20171019145807.23251-10-james.morse@arm.com> <20171030074019.GS2166@lvm> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 9174840795 for ; Thu, 2 Nov 2017 08:14:39 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id zWG4QXcfuwTY for ; Thu, 2 Nov 2017 08:14:33 -0400 (EDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 5E5F1406D0 for ; Thu, 2 Nov 2017 08:14:33 -0400 (EDT) In-Reply-To: <20171030074019.GS2166@lvm> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: Christoffer Dall Cc: Jonathan.Zhang@cavium.com, Marc Zyngier , Catalin Marinas , Julien Thierry , Will Deacon , wangxiongfeng2@huawei.com, linux-arm-kernel@lists.infradead.org, Dongjiu Geng , kvmarm@lists.cs.columbia.edu List-Id: kvmarm@lists.cs.columbia.edu Hi Christoffer, On 30/10/17 07:40, Christoffer Dall wrote: > On Thu, Oct 19, 2017 at 03:57:55PM +0100, James Morse wrote: >> Non-VHE systems take an exception to EL2 in order to world-switch into the >> guest. When returning from the guest KVM implicitly restores the DAIF >> flags when it returns to the kernel at EL1. >> >> With VHE none of this exception-level jumping happens, so KVMs >> world-switch code is exposed to the host kernel's DAIF values, and KVM >> spills the guest-exit DAIF values back into the host kernel. >> On entry to a guest we have Debug and SError exceptions unmasked, KVM >> has switched VBAR but isn't prepared to handle these. On guest exit >> Debug exceptions are left disabled once we return to the host and will >> stay this way until we enter user space. >> >> Add a helper to mask/unmask DAIF around VHE guests. The unmask can only >> happen after the hosts VBAR value has been synchronised by the isb in >> __vhe_hyp_call (via kvm_call_hyp()). Masking could be as late as >> setting KVMs VBAR value, but is kept here for symmetry. > Reviewed-by: Christoffer Dall Thanks! >> --- >> Give me a kick if you want this reworked as a fix (which will then >> conflict with this series), or a backportable version. > > I don't know of any real-world issues where some more graceful handling > of SErrors would make sense on older kernels, so I'm fine with just > merging this together with this series. What about debug? > On guest exit Debug exceptions are left disabled once we return to the host > and will stay this way until we enter user space. Today VHE:KVM causes the kernel to run with SError unmasked and debug disabled until the next return to user-space, whereas previously the kernel expected SError to be masked and debug enabled. (Reposting just the SError rework without this patch changes the kernel to expect SError to be unmasked, which isn't making this any worse.) Thanks, James