Re: [PATCH v10 062/108] KVM: x86/tdp_mmu: implement MapGPA hypercall for TDX

Isaku Yamahata
2022-12-16T00:31:14Z

On Fri, Dec 09, 2022 at 12:01:30AM +0000,
Vishal Annapurve <vannapurve@google.com> wrote:

> > +int __kvm_mmu_map_gpa(struct kvm *kvm, gfn_t *startp, gfn_t end,
> > + bool map_private)
> > +{
> > + gfn_t start = *startp;
> > + int attr;
> > + int ret;
> > +
> > + if (!kvm_gfn_shared_mask(kvm))
> > + return -EOPNOTSUPP;
> > +
> > + attr = map_private ? KVM_MEM_ATTR_PRIVATE : KVM_MEM_ATTR_SHARED;
> > + start = start & ~kvm_gfn_shared_mask(kvm);
> > + end = end & ~kvm_gfn_shared_mask(kvm);
> > +
> > + /*
> > + * To make the following kvm_vm_set_mem_attr() success within spinlock
> > + * without memory allocation.
> > + */
> > + ret = kvm_vm_reserve_mem_attr(kvm, start, end);
> > + if (ret)
> > + return ret;
> > +
> > + write_lock(&kvm-> mmu_lock);
> > + if (is_tdp_mmu_enabled(kvm)) {
> > + gfn_t s = start;
> > +
> > + ret = kvm_tdp_mmu_map_gpa(kvm, &s, end, map_private);
> > + if (!ret) {
> > + KVM_BUG_ON(kvm_vm_set_mem_attr(kvm, attr, start, end), kvm);
>
> This will result in no exits to userspace during memory conversion requests from
> guests. And as a result, userspace will not be able to explicitly back/unback
> shared/private memory during conversions leading to double allocation of memory.
>
> Is this an intended behavior for memory conversion with TDX VMs as per earlier
> discussion?

It was because UPM ioctl interface was not stable yet. With v10, it seems mostly
stable, I'll change the patch of "[PATCH v10 101/108] KVM: TDX: Handle TDX PV
map_gpa hypercall" to exit to user space.
--
Isaku Yamahata <isaku.yamahata@gmail.com>