Re: Userspace MSR handling

[Avi Kivity <avi@redhat.com>]

Gerd Hoffmann wrote:
> On 05/24/09 14:07, Avi Kivity wrote:
>> I agree however that the Xen hypercall page protocol has no business in
>> kvm.ko. But can't we implement it in emu? Xenner conveniently places a
>> ring 0 stub in the guest, we could trap the MSR there and emulate it
>> entirely in the guest.
>
> No.  The case where handling the msr writes is needed is the pv-on-hvm 
> driver support.  For pv kernels it could be handled by emu if it would 
> be needed, but pv kernels don't need the msr stuff in the first place. 
> There should be a longish mail about that in the list archive ...

Yes, I forgot.

Device drivers have no business writing to cpu model specific 
registers.  I hate to bring that fugliness to kvm but I do want to 
support Xen guests.

It should have been implemented as mmio.  Maybe implement an ioctl that 
converts rdmsr/wrmsr to equivalent mmios?

struct kvm_msr_mmio {
    __u32 msr;
    __u32 nr;
    __u64 mmio;
    __u32 flags;
    __u32 pad[3];
}

In any case it should reject the standard msr ranges to prevent Alex 
from implementing cpu emulation in userspace.

-- 
error compiling committee.c: too many arguments to function