On Mon, Apr 22, 2024 at 12:58 PM Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx> wrote:
> > In some cases, it is necessary to defer the preparation of the pages to
> > handle things like in-place encryption of initial guest memory payloads
> > before marking these pages as 'private'/'guest-owned'. Add an argument
> > (always true for now) to kvm_gmem_get_folio() that allows for the
> > preparation callback to be bypassed. To detect possible issues in
>
> IIUC, we have 2 dedicated flows.
> 1 kvm_gmem_get_pfn() or kvm_gmem_allocate()
> a. kvm_gmem_get_folio()
> b. gmem_prepare() for RMP
>
> 2 in-place encryption or whatever
> a. kvm_gmem_get_folio(FGP_CREAT_ONLY)
> b. in-place encryption
> c. gmem_prepare() for RMP
>
> Could we move gmem_prepare() out of kvm_gmem_get_folio(), then we could
> have straightforward flow for each case, and don't have to have an
> argument to pospone gmem_prepare().
There are 3 flows as you note above - kvm_gmem_get_pfn() and
kvm_gmem_allocate() are different paths but they all need to call the
prepare hook. It is a tempting idea to pull kvm_gmem_prepare_folio()
to the two functions (get_pfn and allocate) but the resulting code is
really ugly due to folio_unlock/folio_put.
> > -static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
> > +#ifdef CONFIG_HAVE_KVM_GMEM_PREPARE
> > +bool __weak kvm_arch_gmem_prepare_needed(struct kvm *kvm)
> > +{
> > + return false;
> > +}
> > +#endif
>
> In which case HAVE_KVM_GMEM_PREPARE is selected but
> gmem_prepare_needed() is never implemented? Then all gmem_prepare stuff
> are actually dead code. Maybe we don't need this weak stub?
It's not needed indeed.
> > + if (prepare) {
> > + int r = kvm_gmem_prepare_folio(inode, index, folio);
> > + if (r < 0) {
> > + folio_unlock(folio);
> > + folio_put(folio);
> > + return ERR_PTR(r);
> > + }
> > + }
> > +
>
> Do we still need to prepare the page if it is hwpoisoned? I see the
> hwpoisoned check is outside, in kvm_gmem_get_pfn().
Yep, it can be moved here.
Paolo
