kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Thomas Huth <thuth@redhat.com>
To: Cornelia Huck <cohuck@redhat.com>, David Hildenbrand <david@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
	frankja@linux.ibm.com, kvm@vger.kernel.org,
	linux-s390@vger.kernel.org, stable@kernel.org
Subject: Re: [PATCH/FIXUP FOR STABLE BEFORE THIS SERIES] KVM: s390: do not clobber user space fpc during guest reset
Date: Thu, 30 Jan 2020 11:56:48 +0100	[thread overview]
Message-ID: <336905ea-dc59-3118-9329-fc29c8386c52@redhat.com> (raw)
In-Reply-To: <20200130113941.78e4bf2e.cohuck@redhat.com>

On 30/01/2020 11.39, Cornelia Huck wrote:
> On Thu, 30 Jan 2020 10:49:35 +0100
> David Hildenbrand <david@redhat.com> 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 <borntraeger@de.ibm.com>
>>> ---
>>>  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?

 Thomas


  reply	other threads:[~2020-01-30 10:56 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-29 20:03 [PATCH v8 0/4] KVM: s390: Add new reset vcpu API Janosch Frank
2020-01-29 20:03 ` [PATCH v8 1/4] " Janosch Frank
2020-01-30  8:55   ` [PATCH/FIXUP FOR STABLE BEFORE THIS SERIES] KVM: s390: do not clobber user space fpc during guest reset Christian Borntraeger
2020-01-30  9:49     ` David Hildenbrand
2020-01-30 10:39       ` Cornelia Huck
2020-01-30 10:56         ` Thomas Huth [this message]
2020-01-30 11:07           ` Christian Borntraeger
2020-01-30 11:01       ` Christian Borntraeger
2020-01-30 11:14         ` Christian Borntraeger
2020-01-30 11:20           ` David Hildenbrand
2020-01-30 11:27             ` Christian Borntraeger
2020-01-30 11:42               ` [PATCH v2] KVM: s390: do not clobber user space registers during guest reset/store status Christian Borntraeger
2020-01-30 11:44                 ` Christian Borntraeger
2020-01-30 12:01                 ` Christian Borntraeger
2020-01-30 12:38                   ` David Hildenbrand
2020-01-30  9:00   ` [PATCH v8 1/4] KVM: s390: Add new reset vcpu API Thomas Huth
2020-01-30  9:58   ` Christian Borntraeger
2020-01-29 20:03 ` [PATCH v8 2/4] selftests: KVM: Add fpu and one reg set/get library functions Janosch Frank
2020-01-30 10:36   ` Thomas Huth
2020-01-30 13:55     ` Andrew Jones
2020-01-30 14:10       ` Janosch Frank
2020-01-30 14:30         ` Andrew Jones
2020-01-30 14:58           ` Janosch Frank
2020-01-30 15:04             ` Andrew Jones
2020-01-29 20:03 ` [PATCH v8 3/4] selftests: KVM: s390x: Add reset tests Janosch Frank
2020-01-30 10:51   ` Thomas Huth
2020-01-30 11:32     ` Janosch Frank
2020-01-30 11:36       ` Thomas Huth
2020-01-29 20:03 ` [PATCH v8 4/4] selftests: KVM: testing the local IRQs resets Janosch Frank
2020-01-30 10:55   ` Cornelia Huck
2020-01-30 11:18     ` Janosch Frank
2020-01-30 11:28       ` Cornelia Huck
2020-01-30 11:34         ` Janosch Frank
2020-01-30 11:10   ` Thomas Huth
2020-01-30 11:33     ` Janosch Frank
2020-01-30  9:10 ` [PATCH] KVM: s390: Cleanup initial cpu reset Janosch Frank

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=336905ea-dc59-3118-9329-fc29c8386c52@redhat.com \
    --to=thuth@redhat.com \
    --cc=borntraeger@de.ibm.com \
    --cc=cohuck@redhat.com \
    --cc=david@redhat.com \
    --cc=frankja@linux.ibm.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=stable@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).