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

On Tue, Mar 24, 2026 at 10:46:45AM +0000, Vincent Donnefort wrote:
> 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 protected]>
> > ---
> >  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.

Ack,

> 
> > +};
> > +
> > +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.


I looked at this and tried to implement it this way as you suggest because it is more
elegant but then I realized that `fix_host_ownership_walker` doesn't do
well with MMIO (it returns -EINVAL).

> 
> > +			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
> > 

Thanks Sebastian