[PATCH v2 04/18] KVM: arm64: Add a heap allocator for the pKVM hyp

[Fuad Tabba]

On Tue, 14 Jul 2026 at 19:35, Fuad Tabba <fuad.tabba at linux.dev> wrote:
>
> On Mon, 6 Jul 2026 at 18:54, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> ...
>
> > +static u32 chunk_hash_compute(const struct chunk_hdr *chunk)
> > +{
> > +       u32 hash = 0;
> > +
> > +       BUILD_BUG_ON(sizeof(*chunk) != 16);
> > +
> > +       hash ^= hash_64(*(const u64 *)chunk, 32);
> > +       hash ^= hash_32(chunk->__unmapped, 32);
>
> Could you state the threat model in the commit msg? The VA range is
> hyp-private and the hash is unkeyed (anything that can write EL2
> memory recomputes it), so this only catches _accidental_ corruption,
> i.e. a debug aid.
>
> Since that's the goal, should it be gated on CONFIG_NVHE_EL2_DEBUG
> like the other checks here? As written it's O(n) hashing per
> hyp_alloc(), in production, for a check that only fires on a hyp bug.
> And a plain XOR/additive checksum would be cheaper and just as good
> for accidental corruption.

Thinking about it, I was wrong to say that it would be just as good,
slightly cheaper, but it would detect things like swaps.

Still, I think this should be gated.

Cheers,
/fuad

>
> > +       return hash;
> > +}
> > +
>
> ...
>
>
> > diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> > index 75b00c323310..1c10cf78c869 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> > @@ -10,6 +10,7 @@
> >  #include <asm/kvm_pgtable.h>
> >  #include <asm/kvm_pkvm.h>
> >
> > +#include <nvhe/alloc.h>
> >  #include <nvhe/early_alloc.h>
> >  #include <nvhe/ffa.h>
> >  #include <nvhe/gfp.h>
> > @@ -363,6 +364,10 @@ int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long *per_cpu_bas
> >         if (ret)
> >                 return ret;
> >
> > +       ret = hyp_alloc_init(SZ_128M);
>
> Where does 128M come from? A comment would help.
>
> Cheers,
> /fuad
>
>
>
> > +       if (ret)
> > +               return ret;
> > +
> >         update_nvhe_init_params();
> >
> >         /* Jump in the idmap page to switch to the new page-tables */
> > --
> > 2.55.0.rc2.803.g1fd1e6609c-goog
> >