From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:45631 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726885AbgA3LU2 (ORCPT ); Thu, 30 Jan 2020 06:20:28 -0500 Subject: Re: [PATCH/FIXUP FOR STABLE BEFORE THIS SERIES] KVM: s390: do not clobber user space fpc during guest reset References: <20200129200312.3200-2-frankja@linux.ibm.com> <1580374500-31247-1-git-send-email-borntraeger@de.ibm.com> <7b40856d-8153-ad3f-bea8-110fa6e1aea6@redhat.com> <7711b8a0-f126-aedd-f22b-748fa62cd437@de.ibm.com> <1620d717-b7c3-09d6-8986-a11804c12a41@de.ibm.com> From: David Hildenbrand Message-ID: <4d8ff98b-1d11-d1fa-194d-9fe1e842f7d2@redhat.com> Date: Thu, 30 Jan 2020 12:20:15 +0100 MIME-Version: 1.0 In-Reply-To: <1620d717-b7c3-09d6-8986-a11804c12a41@de.ibm.com> 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: Christian Borntraeger , frankja@linux.ibm.com Cc: cohuck@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, thuth@redhat.com, stable@kernel.org On 30.01.20 12:14, Christian Borntraeger wrote: > > > On 30.01.20 12:01, Christian Borntraeger wrote: >> >> >> On 30.01.20 10:49, David Hildenbrand wrote: >>> On 30.01.20 09:55, Christian Borntraeger wrote: >>>> The initial CPU reset currently clobbers the userspace fpc. This was an >>>> oversight during a fixup for the lazy fpu reloading rework. The reset >>>> calls are only done from userspace ioctls. No CPU context is loaded, so >>>> we can (and must) act directly on the sync regs, not on the thread >>>> context. Otherwise the fpu restore call will restore the zeroes fpc to >>>> userspace. >>>> >>>> Cc: stable@kernel.org >>>> Fixes: 9abc2a08a7d6 ("KVM: s390: fix memory overwrites when vx is disabled") >>>> Signed-off-by: Christian Borntraeger >>>> --- >>>> arch/s390/kvm/kvm-s390.c | 3 +-- >>>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>> >>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>> index c059b86..eb789cd 100644 >>>> --- a/arch/s390/kvm/kvm-s390.c >>>> +++ b/arch/s390/kvm/kvm-s390.c >>>> @@ -2824,8 +2824,7 @@ static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu) >>>> vcpu->arch.sie_block->gcr[14] = CR14_UNUSED_32 | >>>> CR14_UNUSED_33 | >>>> CR14_EXTERNAL_DAMAGE_SUBMASK; >>>> - /* make sure the new fpc will be lazily loaded */ >>>> - save_fpu_regs(); >>>> + vcpu->run->s.regs.fpc = 0; >>>> current->thread.fpu.fpc = 0; >>>> vcpu->arch.sie_block->gbea = 1; >>>> vcpu->arch.sie_block->pp = 0; >>>> >>> >>> kvm_arch_vcpu_ioctl() does a vcpu_load(vcpu), followed by the call to >>> kvm_arch_vcpu_ioctl_initial_reset(), followed by a vcpu_put(). >>> >>> What am I missing? >> >> vcpu_load/put does no longer reload the registers lazily. We moved that out into the >> vcpu_run ioctl itself. (this avoids register reloading during schedule). > > see > e1788bb KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load > 31d8b8d KVM: s390: handle access registers in the run ioctl not in vcpu_put/load > > so maybe we want to change the Fixes tag to this patch. > Yes, because e1788bb KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load broke it. We should audit all users of save_fpu_regs(). -- Thanks, David / dhildenb