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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: David Hildenbrand <david@redhat.com>, frankja@linux.ibm.com
Cc: cohuck@redhat.com, kvm@vger.kernel.org,
	linux-s390@vger.kernel.org, thuth@redhat.com, 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 12:01:17 +0100	[thread overview]
Message-ID: <7711b8a0-f126-aedd-f22b-748fa62cd437@de.ibm.com> (raw)
In-Reply-To: <7b40856d-8153-ad3f-bea8-110fa6e1aea6@redhat.com>



On 30.01.20 10:49, 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 <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?

vcpu_load/put does no longer reload the registers lazily. We moved that out into the
vcpu_run ioctl itself. (this avoids register reloading during schedule).


  parent reply	other threads:[~2020-01-30 11:01 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
2020-01-30 11:01       ` Christian Borntraeger [this message]
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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