On Wed, Apr 24, 2024, Sean Christopherson wrote:
> On Thu, Apr 04, 2024, Paolo Bonzini wrote:
> > In preparation for adding a function that walks a set of pages
> > provided by userspace and populates them in a guest_memfd,
> > add a version of kvm_gmem_get_pfn() that has a "bool prepare"
> > argument and passes it down to kvm_gmem_get_folio().
> >
> > Populating guest memory has to call repeatedly __kvm_gmem_get_pfn()
> > on the same file, so make the new function take struct file*.
> >
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > ---
> > virt/kvm/guest_memfd.c | 38 +++++++++++++++++++++++---------------
> > 1 file changed, 23 insertions(+), 15 deletions(-)
> >
> > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> > index 486748e65f36..a537a7e63ab5 100644
> > --- a/virt/kvm/guest_memfd.c
> > +++ b/virt/kvm/guest_memfd.c
> > @@ -540,33 +540,29 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
> > fput(file);
> > }
> >
> > -int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> > - gfn_t gfn, kvm_pfn_t *pfn, int *max_order)
> > +static int __kvm_gmem_get_pfn(struct file *file, struct kvm_memory_slot *slot,
> > + gfn_t gfn, kvm_pfn_t *pfn, int *max_order, bool prepare)
>
> I genuinely don't know what it means to "prepare" a guest_memfd. I see it becomes
>
> if (!prepare)
> fgp_flags |= FGP_CREAT_ONLY;
>
> but I find the name "prepare" to be extremely unhelpful.
Ah, I'm blind. Maybe "do_prepare", or "do_arch_prepare"? To make it clear that
it's a command, not a description of the operation (which is how I first read it).
And I feel like overloading it to also mean FGP_CREAT_ONLY when _not_ preparing
the memory is odd.
if (prepare) {
int r = kvm_gmem_prepare_folio(inode, index, folio);
if (r < 0) {
folio_unlock(folio);
folio_put(folio);
return ERR_PTR(r);
}
}
Instead of "prepare" as a command, would it make sense to describe the "populating"
case? Because I think it's more intuitive that populating _needs_ to operate on
new, unprepared data.
