Re: [PATCH v10 2/9] KVM: Introduce per-page memory attributes

[Chao Peng]

On Fri, Dec 16, 2022 at 04:09:06PM +0100, Borislav Petkov wrote:
> On Fri, Dec 02, 2022 at 02:13:40PM +0800, Chao Peng wrote:
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 1782c4555d94..7f0f5e9f2406 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1150,6 +1150,9 @@ static struct kvm *kvm_create_vm(unsigned long type, 
> > const char *fdname)
> >     spin_lock_init(&kvm->mn_invalidate_lock);
> >     rcuwait_init(&kvm->mn_memslots_update_rcuwait);
> >     xa_init(&kvm->vcpu_array);
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +   xa_init(&kvm->mem_attr_array);
> > +#endif
> 
>       if (IS_ENABLED(CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES))
>               ...
> 
> would at least remove the ugly ifdeffery.
> 
> Or you could create wrapper functions for that xa_init() and
> xa_destroy() and put the ifdeffery in there.

Agreed.

> 
> > @@ -2323,6 +2329,49 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm 
> > *kvm,
> >  }
> >  #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
> >  
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static u64 kvm_supported_mem_attributes(struct kvm *kvm)
> 
> I guess that function should have a verb in the name:
> 
> kvm_get_supported_mem_attributes()

Right!
> 
> > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
> > +                                      struct kvm_memory_attributes *attrs)
> > +{
> > +   gfn_t start, end;
> > +   unsigned long i;
> > +   void *entry;
> > +   u64 supported_attrs = kvm_supported_mem_attributes(kvm);
> > +
> > +   /* flags is currently not used. */
> > +   if (attrs->flags)
> > +           return -EINVAL;
> > +   if (attrs->attributes & ~supported_attrs)
> > +           return -EINVAL;
> > +   if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
> > +           return -EINVAL;
> > +   if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
> > +           return -EINVAL;
> 
> Dunno, shouldn't those issue some sort of an error message so that the
> caller knows where it failed? Or at least return different retvals which
> signal what the problem is?

Tamping down with error number a bit:

        if (attrs->flags)
                return -ENXIO;
        if (attrs->attributes & ~supported_attrs)
                return -EOPNOTSUPP;
        if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size) ||
            attrs->size == 0)
                return -EINVAL;
        if (attrs->address + attrs->size < attrs->address)
                return -E2BIG;

Chao
> 
> > +   start = attrs->address >> PAGE_SHIFT;
> > +   end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;
> > +
> > +   entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
> > +
> > +   mutex_lock(&kvm->lock);
> > +   for (i = start; i < end; i++)
> > +           if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> > +                               GFP_KERNEL_ACCOUNT)))
> > +                   break;
> > +   mutex_unlock(&kvm->lock);
> > +
> > +   attrs->address = i << PAGE_SHIFT;
> > +   attrs->size = (end - i) << PAGE_SHIFT;
> > +
> > +   return 0;
> > +}
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette