From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:48642 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726873AbgA3Jtt (ORCPT ); Thu, 30 Jan 2020 04:49:49 -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> From: David Hildenbrand Message-ID: <7b40856d-8153-ad3f-bea8-110fa6e1aea6@redhat.com> Date: Thu, 30 Jan 2020 10:49:35 +0100 MIME-Version: 1.0 In-Reply-To: <1580374500-31247-1-git-send-email-borntraeger@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 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? (we could get rid of the kvm_arch_vcpu_ioctl_initial_reset() wrapper) -- Thanks, David / dhildenb