Re: [PATCH v7 02/11] KVM: pfncache: add a mark-dirty helper

[Paul Durrant]

On 31/10/2023 23:28, Sean Christopherson wrote:
> On Mon, Oct 02, 2023, Paul Durrant wrote:
> > From: Paul Durrant <pdurrant@xxxxxxxxxx>
> >
> > At the moment pages are marked dirty by open-coded calls to
> > mark_page_dirty_in_slot(), directly deferefencing the gpa and memslot
> > from the cache. After a subsequent patch these may not always be set
> > so add a helper now so that caller will protected from the need to know
> > about this detail.
> >
> > NOTE: Pages are now marked dirty while the cache lock is held. This is
> >        to ensure that gpa and memslot are mutually consistent.
>
> This absolutely belongs in a separate patch.  It sounds like a bug fix (haven't
> spent the time to figure out if it actually is), and even if it doesn't fix
> anything, burying something like this in a "add a helper" patch is just mean.

Ok, I can split it out. It's a pretty minor fix so didn't seem worth it.

> > diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> > index 0f36acdf577f..b68ed7fa56a2 100644
> > --- a/virt/kvm/pfncache.c
> > +++ b/virt/kvm/pfncache.c
> > @@ -386,6 +386,12 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
> >   }
> >   EXPORT_SYMBOL_GPL(kvm_gpc_activate);
> >   
> > +void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
> > +{
>
> If there's actually a reason to call mark_page_dirty_in_slot() while holding @gpc's
> lock, then this should have a lockdep.  If there's no good reason, then don't move
> the invocation.
>
> > +	mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_gpc_mark_dirty);
>
> This doesn't need to be exported.  Hrm, none of the exports in this file are
> necessary, they likely all got added when we were thinking this stuff would be
> used for nVMX.  I think we should remove them, not because I'm worried about
> sub-modules doing bad things, but just because we should avoid polluting exported
> symbols as much as possible.

That in a separate clean-up patch too, I assume?

  Paul