From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Borntraeger <borntraeger@de.ibm.com>
Subject: Re: [PATCH 3/3] kvm-s390: provide standard guest registers via kvm_run
Date: Wed, 04 Jan 2012 09:30:23 +0100
Message-ID: <4F040E1F.6050806@de.ibm.com>
References: <20111222115646.248800653@de.ibm.com> <1325605858-30492-1-git-send-email-borntraeger@de.ibm.com> <1325605858-30492-4-git-send-email-borntraeger@de.ibm.com> <20120104081646.GA2522@osiris.boeblingen.de.ibm.com>
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Cc: Avi Kivity <avi@redhat.com>, Marcelo Tossati <mtosatti@redhat.com>,
	Carsten Otte <cotte@de.ibm.com>,
	Alexander Graf <agraf@suse.de>,
	Jens Freimann <jfrei@linux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	KVM <kvm@vger.kernel.org>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
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On 04/01/12 09:16, Heiko Carstens wrote:
>>  	save_fp_regs(&vcpu->arch.host_fpregs);
>>  	save_access_regs(vcpu->arch.host_acrs);
>> -	vcpu->arch.guest_fpregs.fpc &= FPC_VALID_MASK;
>> -	restore_fp_regs(&vcpu->arch.guest_fpregs);
>> -	restore_access_regs(vcpu->arch.guest_acrs);
>> +	vcpu->run->sync_rw.fpregs.fpc &= FPC_VALID_MASK;
>> +	restore_fp_regs(&vcpu->run->sync_rw.fpregs);
> 
> ...this is broken, since userspace can update the floating point control
> register contents after the kernel has masked out the offending bits but
> before the register is actually loaded.
> Which in turn could cause a kernel crash, hm?

Indeed, I need to fix that. Thanks for spotting.
I will respin patch 2 and 3 as soon as the interface in patch 1 is settled.

Christian