From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-1.mimecast.com ([207.211.31.81]:47258 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728288AbgDFNWv (ORCPT ); Mon, 6 Apr 2020 09:22:51 -0400 Subject: Re: [PATCH v1 2/5] KVM: s390: vsie: Fix delivery of addressing exceptions References: <20200402184819.34215-1-david@redhat.com> <20200402184819.34215-3-david@redhat.com> <0cd2822e-8486-d386-6c00-faadaa573e5e@de.ibm.com> From: David Hildenbrand Message-ID: <527f7bdf-d8f9-59b4-e70a-54e358ee9e26@redhat.com> Date: Mon, 6 Apr 2020 15:22:42 +0200 MIME-Version: 1.0 In-Reply-To: <0cd2822e-8486-d386-6c00-faadaa573e5e@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Christian Borntraeger , kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Vasily Gorbik , Heiko Carstens , Cornelia Huck , Janosch Frank , stable@vger.kernel.org On 06.04.20 15:17, Christian Borntraeger wrote: > > > On 02.04.20 20:48, 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; > > > kvm_s390_handle_vsie has > > return rc < 0 ? rc : 0; > > > so rc = 0 would result in the same behaviour, correct? yes > Since we DO handle everything as we should, why rc = 1 ? rc == 1 is the internal representation of "we have to go back into g2". rc == 0, in contrast, means "we can go back into g2 (via a NULL intercept) or continue executing g3". Returning rc == 1 instead of rc == 0 at this point is just consistency. -- Thanks, David / dhildenb