Re: [RFC PATCH v11 08/29] KVM: Introduce per-page memory attributes

[Sean Christopherson]

On Mon, Aug 14, 2023, Binbin Wu wrote:
> 
> On 7/19/2023 7:44 AM, Sean Christopherson wrote:
> > +	struct kvm_mmu_notifier_range post_set_range = {
> > +		.start = start,
> > +		.end = end,
> > +		.arg.attributes = attributes,
> > +		.handler = kvm_arch_post_set_memory_attributes,
> > +		.on_lock = (void *)kvm_null_fn,
> > +		.on_unlock = kvm_mmu_invalidate_end,
> > +		.may_block = true,
> > +	};
> > +	unsigned long i;
> > +	void *entry;
> > +	int r;
> > +
> > +	entry = attributes ? xa_mk_value(attributes) : NULL;
> Why attributes of value 0 is considered not a value? Is it because 0 is not
> a valid value when RWX is considered in the future?

0 values don't require an entry in the xarray, i.e. don't need to be stored and
so don't consume memory.  The potential conflict with a RWX=0 entry has already
been noted, but we'll cross that bridge when we get to it, e.g. KVM can easily
support RWX=0 by using an internal "valid" flag.

> Both the changelog and the document added mention that the address and size
> of attrs will be updated to
> "reflect the actual pages of the memory range have been successfully set to
> the attributes", but it doesn't.

Yeah, on the todo list, all of the changelogs are horribly stale.