From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v2 1/3] kvm: svm: Add support for additional SVM NPF error codes Date: Thu, 27 Jul 2017 18:27:49 +0200 Message-ID: References: <147992048887.27638.17559991037474542240.stgit@brijesh-build-machine> <147992049856.27638.17076562184960611399.stgit@brijesh-build-machine> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: thomas.lendacky@amd.com, rkrcmar@redhat.com, joro@8bytes.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, tglx@linutronix.de, bp@suse.de To: Brijesh Singh , kvm@vger.kernel.org Return-path: In-Reply-To: <147992049856.27638.17076562184960611399.stgit@brijesh-build-machine> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 23/11/2016 18:01, Brijesh Singh wrote: > > + /* > + * Before emulating the instruction, check if the error code > + * was due to a RO violation while translating the guest page. > + * This can occur when using nested virtualization with nested > + * paging in both guests. If true, we simply unprotect the page > + * and resume the guest. > + * > + * Note: AMD only (since it supports the PFERR_GUEST_PAGE_MASK used > + * in PFERR_NEXT_GUEST_PAGE) > + */ > + if (error_code == PFERR_NESTED_GUEST_PAGE) { > + kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(cr2)); > + return 1; > + } What happens if L1 is mapping some memory that is read only in L0? That is, the L1 nested page tables make it read-write, but the L0 shadow nested page tables make it read-only. Accessing it would cause an NPF, and then my guess is that the L1 guest would loop on the failing instruction instead of just dropping the write. Paolo