Re: [PATCH 3/3] kvm-s390: provide standard guest registers via kvm_run

[Christian Borntraeger <borntraeger@de.ibm.com>]

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