Re: [PATCH v3 3/7] virt: geniezone: Introduce GenieZone hypervisor support

["Yi-De Wu (吳一德)" <Yi-De.Wu@mediatek.com>]

On Thu, 2023-05-18 at 09:27 +0100, Marc Zyngier wrote:
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> 
> On Fri, 12 May 2023 09:04:01 +0100,
> Yi-De Wu <yi-de.wu@mediatek.com> wrote:
> > 
> > From: "Yingshiuan Pan" <yingshiuan.pan@mediatek.com>
> > 
> > GenieZone is MediaTek hypervisor solution, and it is running in EL2
> > stand alone as a type-I hypervisor. This patch exports a set of
> > ioctl
> > interfaces for userspace VMM (e.g., crosvm) to operate guest VMs
> > lifecycle (creation and destroy) on GenieZone.
> > 
> > Signed-off-by: Yingshiuan Pan <yingshiuan.pan@mediatek.com>
> > Signed-off-by: Yi-De Wu <yi-de.wu@mediatek.com>
> 
> [...]
> 
> > +/**
> > + * gzvm_gfn_to_pfn_memslot() - Translate gfn (guest ipa) to pfn
> > (host pa),
> > + *                          result is in @pfn
> > + *
> > + * Leverage KVM's gfn_to_pfn_memslot(). Because
> > gfn_to_pfn_memslot() needs
> > + * kvm_memory_slot as parameter, this function populates necessary
> > fileds
> > + * for calling gfn_to_pfn_memslot().
> > + *
> > + * Return:
> > + * * 0                       - Succeed
> > + * * -EFAULT         - Failed to convert
> > + */
> > +static int gzvm_gfn_to_pfn_memslot(struct gzvm_memslot *memslot,
> > u64 gfn, u64 *pfn)
> > +{
> > +     hfn_t __pfn;
> > +     struct kvm_memory_slot kvm_slot = {0};
> > +
> > +     kvm_slot.base_gfn = memslot->base_gfn;
> > +     kvm_slot.npages = memslot->npages;
> > +     kvm_slot.dirty_bitmap = NULL;
> > +     kvm_slot.userspace_addr = memslot->userspace_addr;
> > +     kvm_slot.flags = memslot->flags;
> > +     kvm_slot.id = memslot->slot_id;
> > +     kvm_slot.as_id = 0;
> > +
> > +     __pfn = gfn_to_pfn_memslot(&kvm_slot, gfn);
> > +     if (is_error_noslot_pfn(__pfn)) {
> > +             *pfn = 0;
> > +             return -EFAULT;
> > +     }
> 
> I have commented on this before: there is absolutely *no way* that
> you
> can use KVM as the unwilling helper for your stuff. You are passing
> uninitialised data to the core KVM, completely ignoring the semantics
> of all the other fields.
> 
> More importantly, you are now holding us responsible for any breakage
> that would be caused to your code if we change the internals of this
> *PRIVATE FUNCTION*.
> 
> Do you see Xen or Hyper-V using KVM's internals as some sort of
> backend to make their life easier? No, because they understand that
> this is off-limits, and creates an unhealthy dependency for both
> hypervisors.
> 
> So this is a strong NAK. And you can trust me to keep voicing my
> opposition to this sort of horror, wherever I will see these patches.
> 
>         M.
> 
> --
> Without deviation from the norm, progress is not possible.

Noted and fully understood. The patch for this bug fix using our own
implementation would be submitted soon.