Q: What is the struct kvm srcu protecting?

[David Daney <ddaney.cavm@gmail.com>]

Hi,

I am working on the MIPS KVM port, and am trying to figure out under 
which circumstances do I need to srcu_read_lock()/srcu_read_unlock() the 
kvm->srcu.

I am looking at implementing something similar to arch/x86/kvm/x86.c at 
__msr_io(), where we see:

.
.
.
	idx = srcu_read_lock(&vcpu->kvm->srcu);
	for (i = 0; i < msrs->nmsrs; ++i)
		if (do_msr(vcpu, entries[i].index, &entries[i].data))
			break;
	srcu_read_unlock(&vcpu->kvm->srcu, idx);
.
.
.

Why is the srcu_read_lock() taken here?  I see no srcu_dereference() in 
the code path that would indicate the need for obtaining the lock.

I have a feeling that I am missing some essential concept about the 
design of this code, but I don't know what it is.

Can someone explain what is happening here?


Thanks in advance,
David Daney