From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Thomas Huth <thuth@redhat.com>, Cornelia Huck <cohuck@redhat.com>,
David Hildenbrand <david@redhat.com>
Cc: 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 12:07:46 +0100 [thread overview]
Message-ID: <5231e3da-e705-66f8-7426-fdf51cd4600e@de.ibm.com> (raw)
In-Reply-To: <336905ea-dc59-3118-9329-fc29c8386c52@redhat.com>
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 <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?
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).
next prev parent reply other threads:[~2020-01-30 11:07 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
2020-01-30 11:07 ` Christian Borntraeger [this message]
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
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