From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Morse Subject: Re: [PATCH v9 5/7] arm64: kvm: Introduce KVM_ARM_SET_SERROR_ESR ioctl Date: Thu, 15 Feb 2018 17:55:00 +0000 Message-ID: <5A85C974.70500@arm.com> References: <0184EA26B2509940AA629AE1405DD7F201A9E8EA@DGGEMA503-MBS.china.huawei.com> <5A70C5A0.1050600@arm.com> <5A7DDDEE.9050306@arm.com> <93d07d3e-8388-7814-d674-538071d84e2a@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <93d07d3e-8388-7814-d674-538071d84e2a@huawei.com> 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: gengdongjiu Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "corbet@lwn.net" , "marc.zyngier@arm.com" , "catalin.marinas@arm.com" , "linux-doc@vger.kernel.org" , "rjw@rjwysocki.net" , "linux@armlinux.org.uk" , "will.deacon@arm.com" , "robert.moore@intel.com" , "linux-acpi@vger.kernel.org" , "bp@alien8.de" , "lv.zheng@intel.com" , Huangshaoyu , "kvmarm@lists.cs.columbia.edu" , "devel@acpica.org" List-Id: linux-acpi@vger.kernel.org Hi gengdongjiu, On 12/02/18 10:19, gengdongjiu wrote: > On 2018/2/10 1:44, James Morse wrote: >> The point? We can't know what a CPU without the RAS extensions puts in there. >> >> Why Does this matter? When migrating a pending SError we have to know the >> difference between 'use this 64bit value', and 'the CPU will generate it'. >> If I make an SError pending with ESR=0 on a CPU with VSESR, I can't migrated to >> a system that generates an impdef SError-ESR, because I can't know it will be 0. > For the target system, before taking the SError, no one can know whether its syndrome value > is IMPLEMENTATION DEFINED or architecturally defined. For a virtual-SError, the hypervisor knows what it generated. (do I have VSESR_EL2? What did I put in there?). > when the virtual SError is taken, the ESR_ELx.IDS will be updated, then we can know > whether the ESR value is impdef or architecturally defined. True, the guest can't know anything about a pending virtual SError until it takes it. Why is this a problem? > It seems migration is only allowed only when target system and source system all support > RAS extension, because we do not know whether its syndrome is IMPLEMENTATION DEFINED or > architecturally defined. I don't think Qemu allows migration between hosts with differing guest-ID registers. But we shouldn't depend on this, and we may want to hide the v8.2 RAS features from the guest's ID register, but still use them from the host. The way I imagined it working was we would pack the following information into that events struct: { bool serror_pending; bool serror_has_esr; u64 serror_esr; } The problem I was trying to describe is because there is no value of serror_esr we can use to mean 'Ignore this, I'm a v8.0 CPU'. VSESR_EL2 is a 64bit register, any bits we abuse may get a meaning we want to use in the future. When it comes to migration, v8.{0,1} systems can only GET/SET events where serror_has_esr == false, they can't use the serror_esr. On v8.2 systems we should require serror_has_esr to be true. If we need to support migration from v8.{0,1} to v8.2, we can make up an impdef serror_esr. We will need to decide what KVM does when SET is called but an SError was already pending. 2.5.3 "Multiple SError interrupts" of [0] has something to say. Happy new year, James [0] https://static.docs.arm.com/ddi0587/a/RAS%20Extension-release%20candidate_march_29.pdf