Re: [Qemu-devel] [PATCH 4/7 v2] KVM regsync: Add register bitmap parameter to do_kvm_cpu_synchronize_state

[Alexander Graf]

On 24.01.2013, at 19:22, Peter Maydell wrote:

> On 24 January 2013 18:17, Scott Wood <address@hidden> wrote:
>> On 01/24/2013 06:41:05 AM, Alexander Graf wrote:
>>> But maybe the better solution would be a special "write to clear" ONE_REG
>>> register to clear specific bits and a big hammer "set" ONE_REG (which we
>>> have already) for reset only.
>>> 
>>> That would make things easier, right? Scott, any ideas on this?
> 
>> Yes, we should have a ONE_REG write-to-clear TSR.  Maybe a write-to-set
>> version as well, in case userspace wants to inject something.  Likewise for
>> MCSR.
> 
> This would go against the principle we adopted for ARM ONE_REG,
> which is that the "registers" accessed this way never have side
> effects, so userspace could do a complete migration via
> "get complete list of regs; get each reg in list; transfer
> all values to remote end; remote end sets each reg".
> 
> Obviously PPC isn't bound to abide by the same ground rules
> for the ioctl, but I figured I'd mention the principle so
> you can decide if you like it :-)

The "special" register access types wouldn't show up in the "get me all sync 
registers" list. There, we would get the full "read" and "write" accesses to 
TSR and TCR.


Alex