From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:59922 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726893AbgA3LHy (ORCPT ); Thu, 30 Jan 2020 06:07:54 -0500 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 00UB6QQG030061 for ; Thu, 30 Jan 2020 06:07:52 -0500 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 2xtrmce6pm-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 30 Jan 2020 06:07:52 -0500 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 30 Jan 2020 11:07:50 -0000 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> <20200130113941.78e4bf2e.cohuck@redhat.com> <336905ea-dc59-3118-9329-fc29c8386c52@redhat.com> From: Christian Borntraeger Date: Thu, 30 Jan 2020 12:07:46 +0100 MIME-Version: 1.0 In-Reply-To: <336905ea-dc59-3118-9329-fc29c8386c52@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <5231e3da-e705-66f8-7426-fdf51cd4600e@de.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Thomas Huth , Cornelia Huck , David Hildenbrand Cc: frankja@linux.ibm.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, stable@kernel.org On 30.01.20 11:56, Thomas Huth wrote: > On 30/01/2020 11.39, Cornelia Huck wrote: >> On Thu, 30 Jan 2020 10:49:35 +0100 >> 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? >> >> I have been staring at this patch for some time now, and I fear I'm >> missing something as well. Can we please get more explanation? > > Could we please get a test for this issue in the kvm selftests, too? > I.e. host sets a value in its FPC, then calls the INITIAL_RESET ioctl > and then checks that the value in its FPC is still there? Yes, that will come as a later addon patch. (But I am still going to apply this series soon and do not wait for that. I have a private hack in qemu that does this checking, but this test code is too ugly to see the world).