Re: [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions

[Chao Peng]

On Fri, Aug 19, 2022 at 12:37:42PM -0700, Vishal Annapurve wrote:
> > ...
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 230c8ff9659c..bb714c2a4b06 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -914,6 +914,35 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
> >
> >  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
> >
> > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > +#define KVM_MEM_ATTR_PRIVATE   0x0001
> > +static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int 
> > ioctl,
> > +                                            struct kvm_enc_region *region)
> > +{
> > +       unsigned long start, end;
> > +       void *entry;
> > +       int r;
> > +
> > +       if (region->size == 0 || region->addr + region->size < region->addr)
> > +               return -EINVAL;
> > +       if (region->addr & (PAGE_SIZE - 1) || region->size & (PAGE_SIZE - 
> > 1))
> > +               return -EINVAL;
> > +
> > +       start = region->addr >> PAGE_SHIFT;
> > +       end = (region->addr + region->size - 1) >> PAGE_SHIFT;
> > +
> > +       entry = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION ?
> > +                               xa_mk_value(KVM_MEM_ATTR_PRIVATE) : NULL;
> > +
> > +       r = xa_err(xa_store_range(&kvm->mem_attr_array, start, end,
> > +                                       entry, GFP_KERNEL_ACCOUNT));
> 
> xa_store_range seems to create multi-index entries by default.
> Subsequent xa_store_range call changes all the entries stored
> previously.

By using xa_store_range and storing them as multi-index entries I
expected to save some memory for continuous pages originally.

But sounds like the current multi-index store behaviour isn't quite
ready for our usage.

Chao
> xa_store needs to be used here instead of xa_store_range to achieve
> the intended behavior.
> 
> > +
> > +       kvm_zap_gfn_range(kvm, start, end + 1);
> > +
> > +       return r;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_PRIVATE_MEM */
> > +
> > ...