Re: [PATCH v19 09/20] KVM: arm64: Add VM specific callback for S2 MMU operations

[Gavin Shan <gshan@redhat.com>]

On 9/21/26 7:28 AM, Suzuki K Poulose wrote:
> Add VM type specific S2 MMU operation backends which can be initialized per
> VM flavor, to keep the handling cleaner.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>   arch/arm64/include/asm/kvm_host.h |  15 ++++
>   arch/arm64/kvm/mmu.c              | 137 +++++++++++++++++++++++++-----
>   2 files changed, 131 insertions(+), 21 deletions(-)
> 

Apart from the comments from Jonathan, some nitpicks and questions below.

> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 149f4582c8b6a..7664d8b8cce5a 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -155,6 +155,19 @@ struct kvm_vcpu_ops {
>   	void (*vcpu_put)(struct kvm_vcpu *vcpu);
>   };
>   
> +struct kvm_gfn_range;
> +
> +struct kvm_vm_s2_ops {
> +	bool (*vm_age_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
> +	bool (*vm_test_age_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
> +	int (*vm_flush_remote_tlbs)(struct kvm *kvm);
> +	int (*vm_flush_remote_tlbs_range)(struct kvm *kvm, gfn_t gfn,
> +					  u64 nr_pages);
> +	void (*vm_stage2_unmap_range)(struct kvm_s2_mmu *mmu,
> +				      phys_addr_t start, u64 size,
> +				      bool may_block);
> +};
> +
>   struct kvm_s2_mmu {
>   	struct kvm_vmid vmid;
>   
> @@ -332,6 +345,8 @@ struct kvm_arch {
>   	 */
>   	u64 fgu[__NR_FGT_GROUP_IDS__];
>   
> +	const struct kvm_vm_s2_ops *vm_s2_ops;
> +
>   	/*
>   	 * Stage 2 paging state for VMs with nested S2 using a virtual
>   	 * VMID.
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 03f2017a7404a..d97a4a1bca23f 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -37,6 +37,8 @@ static unsigned long __ro_after_init io_map_base;
>   
>   #define KVM_PGT_FN(fn)		(!is_protected_kvm_enabled() ? fn : p ## fn)
>   
> +static int kvm_vm_init_vm_s2_ops(struct kvm *kvm);
> +
>   static phys_addr_t __stage2_range_addr_end(phys_addr_t addr, phys_addr_t end,
>   					   phys_addr_t size)
>   {
> @@ -166,6 +168,18 @@ static bool memslot_is_logging(struct kvm_memory_slot *memslot)
>   	return memslot->dirty_bitmap && !(memslot->flags & KVM_MEM_READONLY);
>   }
>   
> +static int pkvm_flush_remote_tlbs(struct kvm *kvm)
> +{
> +	kvm_call_hyp_nvhe(__pkvm_tlb_flush_vmid, kvm->arch.pkvm.handle);
> +	return 0;
> +}
> +
> +static int kvm_vm_flush_remote_tlbs(struct kvm *kvm)
> +{
> +	kvm_call_hyp(__kvm_tlb_flush_vmid, &kvm->arch.mmu);
> +	return 0;
> +}
> +
>   /**
>    * kvm_arch_flush_remote_tlbs() - flush all VM TLB entries for v7/8
>    * @kvm:	pointer to kvm structure.
> @@ -174,26 +188,36 @@ static bool memslot_is_logging(struct kvm_memory_slot *memslot)
>    */
>   int kvm_arch_flush_remote_tlbs(struct kvm *kvm)
>   {
> -	if (is_protected_kvm_enabled())
> -		kvm_call_hyp_nvhe(__pkvm_tlb_flush_vmid, kvm->arch.pkvm.handle);
> -	else
> -		kvm_call_hyp(__kvm_tlb_flush_vmid, &kvm->arch.mmu);
> -	return 0;
> +	if (!kvm->arch.vm_s2_ops->vm_flush_remote_tlbs)
> +		return 1;

For the return value, I'm wandering if 0 should be returned. More details
can be found below.

> +	return kvm->arch.vm_s2_ops->vm_flush_remote_tlbs(kvm);
>   }
>   
> -int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm,
> -				      gfn_t gfn, u64 nr_pages)
> +static int pkvm_flush_remote_tlbs_range(struct kvm *kvm,
> +					gfn_t gfn, u64 nr_pages)
> +{
> +	return pkvm_flush_remote_tlbs(kvm);
> +}
> +
> +static int kvm_vm_flush_remote_tlbs_range(struct kvm *kvm,
> +					 gfn_t gfn, u64 nr_pages)
>   {
>   	u64 size = nr_pages << PAGE_SHIFT;
>   	u64 addr = gfn << PAGE_SHIFT;
>   
> -	if (is_protected_kvm_enabled())
> -		kvm_call_hyp_nvhe(__pkvm_tlb_flush_vmid, kvm->arch.pkvm.handle);
> -	else
> -		kvm_tlb_flush_vmid_range(&kvm->arch.mmu, addr, size);
> +	kvm_tlb_flush_vmid_range(&kvm->arch.mmu, addr, size);
>   	return 0;
>   }
>   
> +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm,
> +				     gfn_t gfn, u64 nr_pages)
> +{
> +	if (!kvm->arch.vm_s2_ops->vm_flush_remote_tlbs_range)
> +		return 1;
> +

Realm would the only case where vm_s2_ops->vm_flush_remote_{tlbs, tlbs_range)
are NULL. On request to flush remote TLBs by kvm_flush_remote_tlbs_range(), it
ends up with event KVM_REQ_TLB_FLUSH queued for each vCPU. How this queued event
is linked to a remote TLB flush for realm? The problem is TLBs are owned by EL2
realm and there are no RMI calls for the management. So I'm wandering we should
return 0 here?

> +	return kvm->arch.vm_s2_ops->vm_flush_remote_tlbs_range(kvm, gfn, nr_pages);
> +}
> +
>   static void *stage2_memcache_zalloc_page(void *arg)
>   {
>   	struct kvm_mmu_memory_cache *mc = arg;
> @@ -337,13 +361,20 @@ static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64
>   				   may_block));
>   }
>   
> +static void kvm_vm_stage2_unmap_range(struct kvm_s2_mmu *mmu,
> +				      phys_addr_t start,
> +				      u64 size, bool may_block)
> +{
> +	__unmap_stage2_range(mmu, start, size, may_block);
> +}
> +
>   void kvm_stage2_unmap_range(struct kvm_s2_mmu *mmu, phys_addr_t start,
>   			    u64 size, bool may_block)
>   {
> -	if (kvm_vm_is_protected(kvm_s2_mmu_to_kvm(mmu)))
> -		return;
> +	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
>   
> -	__unmap_stage2_range(mmu, start, size, may_block);
> +	if (kvm->arch.vm_s2_ops->vm_stage2_unmap_range)
> +		kvm->arch.vm_s2_ops->vm_stage2_unmap_range(mmu, start, size, may_block);
>   }
>   
>   void kvm_stage2_flush_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_t end)
> @@ -983,6 +1014,12 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
>   	int cpu, err;
>   	struct kvm_pgtable *pgt;
>   
> +	/* Initialize the VM ops for the VM instance for the first time */
> +	if (mmu == &kvm->arch.mmu) {
> +		err = kvm_vm_init_vm_s2_ops(kvm);
> +		if (err)
> +			return err;
> +	}
>   	/*
>   	 * If we already have our page tables in place, and that the
>   	 * MMU context is the canonical one, we have a bug somewhere,
> @@ -2447,34 +2484,46 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>   	return false;
>   }
>   
> -bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> +static bool kvm_vm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
>   {
>   	u64 size = (range->end - range->start) << PAGE_SHIFT;
>   
> -	if (!kvm->arch.mmu.pgt || kvm_vm_is_protected(kvm))
> -		return false;
> -
>   	return KVM_PGT_FN(kvm_pgtable_stage2_test_clear_young)(kvm->arch.mmu.pgt,
>   						   range->start << PAGE_SHIFT,
>   						   size, true);
> +}
> +
> +bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> +{
> +	if (!kvm->arch.mmu.pgt || !kvm->arch.vm_s2_ops->vm_age_gfn)
> +		return false;
> +
> +	return kvm->arch.vm_s2_ops->vm_age_gfn(kvm, range);
>   	/*
>   	 * TODO: Handle nested_mmu structures here using the reverse mapping in
>   	 * a later version of patch series.
>   	 */
>   }
>   
> -bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> +static bool kvm_vm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
>   {
>   	u64 size = (range->end - range->start) << PAGE_SHIFT;
>   
> -	if (!kvm->arch.mmu.pgt || kvm_vm_is_protected(kvm))
> -		return false;
>   
>   	return KVM_PGT_FN(kvm_pgtable_stage2_test_clear_young)(kvm->arch.mmu.pgt,
>   						   range->start << PAGE_SHIFT,
>   						   size, false);
>   }
>   
> +bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> +{
> +
> +	if (!kvm->arch.mmu.pgt || !kvm->arch.vm_s2_ops->vm_test_age_gfn)
> +		return false;
> +
> +	return kvm->arch.vm_s2_ops->vm_test_age_gfn(kvm, range);
> +}
> +
>   phys_addr_t kvm_mmu_get_httbr(void)
>   {
>   	return __pa(hyp_pgtable->pgd);
> @@ -2796,3 +2845,49 @@ void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled)
>   
>   	trace_kvm_toggle_cache(*vcpu_pc(vcpu), was_enabled, now_enabled);
>   }
> +
> +static const struct kvm_vm_s2_ops protected_pkvm_vm_s2_ops = {
> +	.vm_flush_remote_tlbs		= pkvm_flush_remote_tlbs,
> +	.vm_flush_remote_tlbs_range	= pkvm_flush_remote_tlbs_range,
> +	/*
> +	 * Not supported for Protected VMs under pKVM
> +	 * .vm_age_gfn
> +	 * .vm_test_age_gfn
> +	 * .vm_stage2_unmap_range
> +	 */
> +};
> +
> +static const struct kvm_vm_s2_ops pkvm_vm_s2_ops = {
> +	.vm_flush_remote_tlbs		= pkvm_flush_remote_tlbs,
> +	.vm_flush_remote_tlbs_range	= pkvm_flush_remote_tlbs_range,
> +	.vm_age_gfn			= kvm_vm_age_gfn,
> +	.vm_test_age_gfn		= kvm_vm_test_age_gfn,
> +	.vm_stage2_unmap_range		= kvm_vm_stage2_unmap_range,
> +};
> +
> +static const struct kvm_vm_s2_ops kvm_default_vm_s2_ops = {
> +	.vm_flush_remote_tlbs		= kvm_vm_flush_remote_tlbs,
> +	.vm_flush_remote_tlbs_range	= kvm_vm_flush_remote_tlbs_range,
> +	.vm_age_gfn			= kvm_vm_age_gfn,
> +	.vm_test_age_gfn		= kvm_vm_test_age_gfn,
> +	.vm_stage2_unmap_range		= kvm_vm_stage2_unmap_range,
> +};
> +
> +#define KVM_VM_S2_OPS(flavor, ops)		\
> +		[flavor] = ops

Parentheses are needed, to be consistent with KVM_VCPU_OPS at least.

#define KVM_VM_S2_OPS(flavor, ops)		\
		[(flavor)] = (ops)

Actually, KVM_{VCPU, VM_S2}_OPS() can be combined to one in kvm_host.h as below.

#define KVM_FLAVOR_OPS() [(flavor)] = (ops)

> +static const struct kvm_vm_s2_ops *arm64_vm_s2_ops[] = {
> +	KVM_VM_S2_OPS(VM_VHE, &kvm_default_vm_s2_ops),
> +	KVM_VM_S2_OPS(VM_NVHE, &kvm_default_vm_s2_ops),
> +	KVM_VM_S2_OPS(VM_PKVM, &pkvm_vm_s2_ops),
> +	KVM_VM_S2_OPS(VM_PROTECTED_PKVM, &protected_pkvm_vm_s2_ops),
> +};
> +
> +static int kvm_vm_init_vm_s2_ops(struct kvm *kvm)
> +{
> +	BUILD_BUG_ON(ARRAY_SIZE(arm64_vm_s2_ops) != VM_FLAVOR_MAX);
> +
> +	kvm->arch.vm_s2_ops = arm64_vm_s2_ops[kvm->arch.vm_flavor];
> +	if (WARN_ON(!kvm->arch.vm_s2_ops))
> +		return -EINVAL;
> +	return 0;
> +}

Thanks,
Gavin