From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host Date: Thu, 7 Sep 2017 11:13:46 +0100 Message-ID: References: <1504763684-30128-1-git-send-email-gengdongjiu@huawei.com> <59B10F52.9010400@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org To: gengdongjiu , James Morse Cc: christoffer.dall@linaro.org, vladimir.murzin@arm.com, rkrcmar@redhat.com, catalin.marinas@arm.com, shankerd@codeaurora.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, zhanghaibin7@huawei.com, huangshaoyu@huawei.com List-Id: kvmarm@lists.cs.columbia.edu On 07/09/17 11:05, gengdongjiu wrote: > Hi James, > > On 2017/9/7 17:20, James Morse wrote: >> Hi Dongjiu Geng, >> >> On 07/09/17 06:54, Dongjiu Geng wrote: >>> In VHE mode, host kernel runs in the EL2 and can enable >>> 'User Access Override' when fs==KERNEL_DS so that it can >>> access kernel memory. However, PSTATE.UAO is set to 0 on >>> an exception taken from EL1 to EL2. Thus when VHE is used >>> and exception taken from a guest UAO will be disabled and >>> host will use the incorrect PSTATE.UAO. So check and reset >>> the PSTATE.UAO when switching to host. >> >> This would only be a problem if KVM were calling into world-switch with >> fs==KERNEL_DS. I can't see where this happens. > Not only KVM, may also kernel sets the fs == KERNEL_DS before calling into world-switch How? Please describe the exact sequence of event that lead to this situation with the current code base. M. -- Jazz is not dead. It just smells funny...