On 18/10/21 19:14, butt3rflyh4ck wrote:
{
struct kvm_vcpu *vcpu = kvm_get_running_vcpu(); //-------> invoke
kvm_get_running_vcpu() to get a vcpu.
WARN_ON_ONCE(vcpu->kvm != kvm); [1]
return &vcpu->dirty_ring;
}
```
but we had not called KVM_CREATE_VCPU ioctl to create a kvm_vcpu so
vcpu is NULL.
It's not just because there was no call to KVM_CREATE_VCPU; in general
kvm->dirty_ring_size only works if all writes are associated to a
specific vCPU, which is not the case for the one of
kvm_xen_shared_info_init.
David, what do you think? Making dirty-page ring buffer incompatible
with Xen is ugly and I'd rather avoid it; taking the mutex for vcpu 0 is
not an option because, as the reporter said, you might not have even
created a vCPU yet when you call KVM_XEN_HVM_SET_ATTR. The remaining
option would be just "do not mark the page as dirty if the ring buffer
is active". This is feasible because userspace itself has passed the
shared info gfn; but again, it's ugly...
Paolo
