Re: [PATCH 02/14] KVM: arm64: Track host-unmapped MMIO regions in a static array

[Sebastian Ene]

On Thu, Mar 12, 2026 at 07:05:16PM +0000, Fuad Tabba wrote:
> Hi Sebastian,
> 
> On Tue, 10 Mar 2026 at 12:49, Sebastian Ene <sebastianene@xxxxxxxxxx> wrote:
> >
> > Introduce a registry to track protected MMIO regions that are unmapped
> > from the host stage-2 page tables. These regions are stored in a
> > fixed-size array and their ownership is donated to the hypervisor during
> > initialization to ensure host-exclusion and persistent tracking.
> >
> > Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
> > ---
> >  arch/arm64/include/asm/kvm_pkvm.h     | 10 ++++++++++
> >  arch/arm64/kvm/hyp/nvhe/mem_protect.c |  3 +++
> >  arch/arm64/kvm/hyp/nvhe/setup.c       | 25 +++++++++++++++++++++++++
> >  3 files changed, 38 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
> > index 757076ad4ec9..48ec7d519399 100644
> > --- a/arch/arm64/include/asm/kvm_pkvm.h
> > +++ b/arch/arm64/include/asm/kvm_pkvm.h
> > @@ -17,6 +17,16 @@
> >
> >  #define HYP_MEMBLOCK_REGIONS 128
> >
> > +#define PKVM_PROTECTED_REGS_NUM        8
> > +
> > +struct pkvm_protected_reg {
> > +       u64 start_pfn;
> > +       size_t num_pages;
> > +};
> > +
> > +extern struct pkvm_protected_reg kvm_nvhe_sym(pkvm_protected_regs)[];
> > +extern unsigned int kvm_nvhe_sym(num_protected_reg);
> > +
> >  int pkvm_init_host_vm(struct kvm *kvm);
> >  int pkvm_create_hyp_vm(struct kvm *kvm);
> >  bool pkvm_hyp_vm_is_created(struct kvm *kvm);
> > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > index 0808367c52e5..7c125836b533 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> > @@ -23,6 +23,9 @@
> >
> >  struct host_mmu host_mmu;
> >
> > +struct pkvm_protected_reg pkvm_protected_regs[PKVM_PROTECTED_REGS_NUM];
> > +unsigned int num_protected_reg;
> > +
> >  static struct hyp_pool host_s2_pool;
> >
> >  static DEFINE_PER_CPU(struct pkvm_hyp_vm *, __current_vm);
> > diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> > index 90bd014e952f..ad5b96085e1b 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> > @@ -284,6 +284,27 @@ static int fix_hyp_pgtable_refcnt(void)
> >                                 &walker);
> >  }
> >
> > +static int unmap_protected_regions(void)
> 
> I think the name of this function is confusing. It's not really
> unmapping, it's donating the regions to hyp. Maybe
> donate_protected_regions() or claim_protected_mmio_regions to reflect
> that we are doing an ownership transfer?

I renamed it to donate_protected_mmio_regions to make it more clear in
regards to what it does. 

> 
> > +{
> > +       struct pkvm_protected_reg *reg;
> > +       int i, ret, j = 0;
> 
> Please don't interleave the iterators with ret. Moreover, you can
> define ret inside the loop below. Also, you don't need to initialze j.
> 
> > +
> > +       for (i = 0; i < num_protected_reg; i++) {
> > +               reg = &pkvm_protected_regs[i];
> > +               for (j = 0; j < reg->num_pages; j++) {
> > +                       ret = __pkvm_host_donate_hyp_mmio(reg->start_pfn + j);
> > +                       if (ret)
> > +                               goto err_setup;
> > +               }
> > +       }
> > +
> > +       return 0;
> > +err_setup:
> > +       for (j = j - 1; j >= 0; j--)
> > +               __pkvm_hyp_donate_host_mmio(reg->start_pfn + j);
> 
> This rolls back the regions only for the latest `i` iteration, not all
> the `i` iterations.
>

I re-wrote this bit since the last version of the
__pkvm_host_donate_hyp_mmio accepts a size as well.

> How about (not tested):
> 
> +    err_setup:
> +       while (j--)
> +           __pkvm_hyp_donate_host_mmio(reg->start_pfn + j);
> +
> +       while (i--) {
> +           reg = &pkvm_protected_regs[i];
> +           for (j = reg->num_pages - 1; j >= 0; j--)
> +               __pkvm_hyp_donate_host_mmio(reg->start_pfn + j);
> +       }
> 
> Thanks,
> /fuad
> 

Cheers,
Sebastian

> 
> > +       return ret;
> > +}
> > +
> >  void __noreturn __pkvm_init_finalise(void)
> >  {
> >         struct kvm_cpu_context *host_ctxt = host_data_ptr(host_ctxt);
> > @@ -324,6 +345,10 @@ void __noreturn __pkvm_init_finalise(void)
> >         if (ret)
> >                 goto out;
> >
> > +       ret = unmap_protected_regions();
> > +       if (ret)
> > +               goto out;
> > +
> >         ret = hyp_ffa_init(ffa_proxy_pages);
> >         if (ret)
> >                 goto out;
> > --
> > 2.53.0.473.g4a7958ca14-goog
> >