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([2601:646:c200:1ef2:51ac:4d36:2f8d:8208]) by smtp.gmail.com with ESMTPSA id d22sm6733429pgg.52.2020.01.30.07.18.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jan 2020 07:18:15 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 2/2] KVM: VMX: Extend VMX's #AC handding Date: Thu, 30 Jan 2020 07:18:14 -0800 Message-Id: <4A8E14B3-1914-4D0C-A43A-234717179408@amacapital.net> References: <20200130121939.22383-3-xiaoyao.li@intel.com> Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Paolo Bonzini , Sean Christopherson , x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org In-Reply-To: <20200130121939.22383-3-xiaoyao.li@intel.com> To: Xiaoyao Li X-Mailer: iPhone Mail (17C54) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jan 30, 2020, at 4:24 AM, Xiaoyao Li wrote: >=20 > =EF=BB=BFThere are two types of #AC can be generated in Intel CPUs: > 1. legacy alignment check #AC; > 2. split lock #AC; >=20 > Legacy alignment check #AC can be injected to guest if guest has enabled > alignemnet check. >=20 > When host enables split lock detection, i.e., split_lock_detect!=3Doff, > guest will receive an unexpected #AC when there is a split_lock happens in= > guest since KVM doesn't virtualize this feature to guest. >=20 > Since the old guests lack split_lock #AC handler and may have split lock > buges. To make guest survive from split lock, applying the similar policy > as host's split lock detect configuration: > - host split lock detect is sld_warn: > warning the split lock happened in guest, and disabling split lock > detect around VM-enter; > - host split lock detect is sld_fatal: > forwarding #AC to userspace. (Usually userspace dump the #AC > exception and kill the guest). A correct userspace implementation should, with a modern guest kernel, forwa= rd the exception. Otherwise you=E2=80=99re introducing a DoS into the guest i= f the guest kernel is fine but guest userspace is buggy. What=E2=80=99s the intended behavior here?=