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Thu, 30 Jan 2020 07:38:57 -0500 X-MC-Unique: -1p4fRIlPvmlHG6IQF1J4A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5E6FB100550E; Thu, 30 Jan 2020 12:38:56 +0000 (UTC) Received: from [10.36.117.219] (ovpn-117-219.ams2.redhat.com [10.36.117.219]) by smtp.corp.redhat.com (Postfix) with ESMTP id 703D587B14; Thu, 30 Jan 2020 12:38:54 +0000 (UTC) Subject: Re: [PATCH v2] KVM: s390: do not clobber user space registers during guest reset/store status To: Christian Borntraeger Cc: cohuck@redhat.com, frankja@linux.ibm.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, stable@kernel.org, thuth@redhat.com References: <7d031d9c-e2f6-73bf-c4d6-6e2753d9102f@de.ibm.com> <1580384552-7964-1-git-send-email-borntraeger@de.ibm.com> <8120c228-2935-07d4-38b9-3b9c5cb8b92c@de.ibm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <8120c228-2935-07d4-38b9-3b9c5cb8b92c@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 30.01.20 13:01, Christian Borntraeger wrote: > > > On 30.01.20 12:42, Christian Borntraeger wrote: >> The two ioctls for initial CPU reset and store status currently clobber >> the userspace fpc and potentially access registers. 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. > > New patch description: > > KVM: s390: do not clobber registers during guest reset/store status > > The initial CPU reset clobbers the userspace fpc and the store status > ioctl clobbers the guest acrs + fpr. As these calls are only done via > ioctl (and not via vcpu_run), no CPU context is loaded, so we can (and > must) act directly on the sync regs, not on the thread context. > > Cc: stable@kernel.org > Fixes: e1788bb995be ("KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load") > Fixes: 31d8b8d41a7e ("KVM: s390: handle access registers in the run ioctl not in vcpu_put/load") > Signed-off-by: Christian Borntraeger > >> >> Cc: stable@kernel.org >> Fixes: e1788bb995be ("KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load") >> Fixes: 31d8b8d41a7e ("KVM: s390: handle access registers in the run ioctl not in vcpu_put/load") >> Signed-off-by: Christian Borntraeger >> --- >> arch/s390/kvm/kvm-s390.c | 5 ++--- >> 1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index c059b86..936415b 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; >> @@ -4343,7 +4342,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp, >> switch (ioctl) { >> case KVM_S390_STORE_STATUS: >> idx = srcu_read_lock(&vcpu->kvm->srcu); >> - r = kvm_s390_vcpu_store_status(vcpu, arg); >> + r = kvm_s390_vcpu_store_status_unloaded(vcpu, arg); >> srcu_read_unlock(&vcpu->kvm->srcu, idx); >> break; >> case KVM_S390_SET_INITIAL_PSW: { >> > With new description + fixed up call Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb