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

[Fuad Tabba]

Hi Sebastian,

On Tue, 10 Mar 2026 at 12:49, Sebastian Ene <sebastianene at google.com> 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 at google.com>
> ---
>  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?

> +{
> +       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.

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


> +       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
>