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

From: Vincent Donnefort <[email-masked]>
Date: Tue, 24 Mar 2026 10:46:45 +0000

On Tue, Mar 10, 2026 at 12:49:21PM +0000, Sebastian Ene 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 <[email-masked]>
> ---
>  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; 

nit: "u64 pfn, u64 nr_pages" to align with everywhere else.

> +};
> +
> +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)
> +{
> +	struct pkvm_protected_reg *reg;
> +	int i, ret, j = 0;
> +
> +	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 this is to make this static at boot, we don't even need __pkvm_host_donate_hyp_mmio()

We can just map the region early enough in the hypervisor pkvm_create_mappings()
in recreate_hyp_mappings() and then let fix_host_ownership() do the host
stage2 unmapping.

> +			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);
> +	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
>