From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:49512 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728500AbgDGLfM (ORCPT ); Tue, 7 Apr 2020 07:35:12 -0400 Subject: Re: [PATCH v2 2/5] KVM: s390: vsie: Fix delivery of addressing exceptions References: <20200403153050.20569-1-david@redhat.com> <20200403153050.20569-3-david@redhat.com> <20200407130013.2898fb57@p-imbrenda> From: David Hildenbrand Message-ID: <7345a3fa-d790-5e9c-dbc0-58cfd1b6101e@redhat.com> Date: Tue, 7 Apr 2020 13:35:00 +0200 MIME-Version: 1.0 In-Reply-To: <20200407130013.2898fb57@p-imbrenda> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Vasily Gorbik , Heiko Carstens , Cornelia Huck , Janosch Frank , Christian Borntraeger , stable@vger.kernel.org On 07.04.20 13:00, Claudio Imbrenda wrote: > On Fri, 3 Apr 2020 17:30:47 +0200 > David Hildenbrand wrote: > >> Whenever we get an -EFAULT, we failed to read in guest 2 physical >> address space. Such addressing exceptions are reported via a program >> intercept to the nested hypervisor. >> >> We faked the intercept, we have to return to guest 2. Instead, right >> now we would be returning -EFAULT from the intercept handler, >> eventually crashing the VM. >> >> Addressing exceptions can only happen if the g2->g3 page tables >> reference invalid g2 addresses (say, either a table or the final page >> is not accessible - so something that basically never happens in sane >> environments. >> >> Identified by manual code inspection. >> >> Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested >> virtualization") Cc: # v4.8+ >> Signed-off-by: David Hildenbrand >> --- >> arch/s390/kvm/vsie.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c >> index 076090f9e666..4f6c22d72072 100644 >> --- a/arch/s390/kvm/vsie.c >> +++ b/arch/s390/kvm/vsie.c >> @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, >> struct vsie_page *vsie_page) scb_s->iprcc = PGM_ADDRESSING; >> scb_s->pgmilc = 4; >> scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4); >> + rc = 1; >> } >> return rc; >> } > > so, the reason why we never noticed this issue before is simply that > nobody tried running a misbehaving nested guest? Yes, actually, a misbehaving nested hypervisor. > > Reviewed-by: Claudio Imbrenda > Thanks! -- Thanks, David / dhildenb