On Mon, Aug 12, 2024, Lai Jiangshan wrote:
> On Sat, Aug 10, 2024 at 3:49 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> > +
> > +static unsigned long kvm_rmap_lock(struct kvm_rmap_head *rmap_head)
> > +{
> > + unsigned long old_val, new_val;
> > +
> > + old_val = READ_ONCE(rmap_head->val);
> > + if (!old_val)
> > + return 0;
> > +
> > + do {
> > + /*
> > + * If the rmap is locked, wait for it to be unlocked before
> > + * trying acquire the lock, e.g. to bounce the cache line.
> > + */
> > + while (old_val & KVM_RMAP_LOCKED) {
> > + old_val = READ_ONCE(rmap_head->val);
> > + cpu_relax();
>
> The sequence of these two lines of code can be improved.
Oh yeah, duh, re-read after PAUSE, not before.
Definitely holler if you have any alternative ideas for walking rmaps without
taking mmu_lock, I guarantee you've spent more time than me thinking about the
shadow MMU :-)
