Re: [PATCH v3 06/21] KVM: arm64: Add support for stage-2 map()/unmap() in generic page-table

[Gavin Shan <gshan@redhat.com>]

Hi Will,

On 8/25/20 7:39 PM, Will Deacon wrote:
> Add stage-2 map() and unmap() operations to the generic page-table code.
> 
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>   arch/arm64/include/asm/kvm_pgtable.h |  39 ++++
>   arch/arm64/kvm/hyp/pgtable.c         | 262 +++++++++++++++++++++++++++
>   2 files changed, 301 insertions(+)
> 

With the following questions resolved:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 3389f978d573..8ab0d5f43817 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -134,6 +134,45 @@ int kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm *kvm);
>    */
>   void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
>   
> +/**
> + * kvm_pgtable_stage2_map() - Install a mapping in a guest stage-2 page-table.
> + * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init().
> + * @addr:	Intermediate physical address at which to place the mapping.
> + * @size:	Size of the mapping.
> + * @phys:	Physical address of the memory to map.
> + * @prot:	Permissions and attributes for the mapping.
> + * @mc:		Cache of pre-allocated GFP_PGTABLE_USER memory from which to
> + *		allocate page-table pages.
> + *
> + * If device attributes are not explicitly requested in @prot, then the
> + * mapping will be normal, cacheable.
> + *
> + * Note that this function will both coalesce existing table entries and split
> + * existing block mappings, relying on page-faults to fault back areas outside
> + * of the new mapping lazily.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
> +			   u64 phys, enum kvm_pgtable_prot prot,
> +			   struct kvm_mmu_memory_cache *mc);
> +
> +/**
> + * kvm_pgtable_stage2_unmap() - Remove a mapping from a guest stage-2 page-table.
> + * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init().
> + * @addr:	Intermediate physical address from which to remove the mapping.
> + * @size:	Size of the mapping.
> + *
> + * TLB invalidation is performed for each page-table entry cleared during the
> + * unmapping operation and the reference count for the page-table page
> + * containing the cleared entry is decremented, with unreferenced pages being
> + * freed. Unmapping a cacheable page will ensure that it is clean to the PoC if
> + * FWB is not supported by the CPU.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size);
> +
>   /**
>    * kvm_pgtable_walk() - Walk a page-table.
>    * @pgt:	Page-table structure initialised by kvm_pgtable_*_init().
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index b8550ccaef4d..41ee8f3c0369 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -32,10 +32,19 @@
>   #define KVM_PTE_LEAF_ATTR_LO_S1_SH_IS	3
>   #define KVM_PTE_LEAF_ATTR_LO_S1_AF	BIT(10)
>   
> +#define KVM_PTE_LEAF_ATTR_LO_S2_MEMATTR	GENMASK(5, 2)
> +#define KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R	BIT(6)
> +#define KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W	BIT(7)
> +#define KVM_PTE_LEAF_ATTR_LO_S2_SH	GENMASK(9, 8)
> +#define KVM_PTE_LEAF_ATTR_LO_S2_SH_IS	3
> +#define KVM_PTE_LEAF_ATTR_LO_S2_AF	BIT(10)
> +
>   #define KVM_PTE_LEAF_ATTR_HI		GENMASK(63, 51)
>   
>   #define KVM_PTE_LEAF_ATTR_HI_S1_XN	BIT(54)
>   
> +#define KVM_PTE_LEAF_ATTR_HI_S2_XN	BIT(54)
> +
>   struct kvm_pgtable_walk_data {
>   	struct kvm_pgtable		*pgt;
>   	struct kvm_pgtable_walker	*walker;
> @@ -420,6 +429,259 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt)
>   	pgt->pgd = NULL;
>   }
>   
> +struct stage2_map_data {
> +	u64				phys;
> +	kvm_pte_t			attr;
> +
> +	kvm_pte_t			*anchor;
> +
> +	struct kvm_s2_mmu		*mmu;
> +	struct kvm_mmu_memory_cache	*memcache;
> +};
> +
> +static kvm_pte_t *stage2_memcache_alloc_page(struct stage2_map_data *data)
> +{
> +	kvm_pte_t *ptep = NULL;
> +	struct kvm_mmu_memory_cache *mc = data->memcache;
> +
> +	/* Allocated with GFP_PGTABLE_USER, so no need to zero */
> +	if (mc && mc->nobjs)
> +		ptep = mc->objects[--mc->nobjs];
> +
> +	return ptep;
> +}
> +

This function is introduced by this (PATCH[6]), but replaced by
the generic one (kvm_mmu_memory_cache_alloc()) in PATCH[7]. I
think we might use the generic one from PATCH[7].

> +static int stage2_map_set_prot_attr(enum kvm_pgtable_prot prot,
> +				    struct stage2_map_data *data)
> +{
> +	bool device = prot & KVM_PGTABLE_PROT_DEVICE;
> +	kvm_pte_t attr = device ? PAGE_S2_MEMATTR(DEVICE_nGnRE) :
> +			    PAGE_S2_MEMATTR(NORMAL);
> +	u32 sh = KVM_PTE_LEAF_ATTR_LO_S2_SH_IS;
> +
> +	if (!(prot & KVM_PGTABLE_PROT_X))
> +		attr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
> +	else if (device)
> +		return -EINVAL;
> +
> +	if (prot & KVM_PGTABLE_PROT_R)
> +		attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
> +
> +	if (prot & KVM_PGTABLE_PROT_W)
> +		attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
> +
> +	attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S2_SH, sh);
> +	attr |= KVM_PTE_LEAF_ATTR_LO_S2_AF;
> +	data->attr = attr;
> +	return 0;
> +}
> +
> +static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
> +				       kvm_pte_t *ptep,
> +				       struct stage2_map_data *data)
> +{
> +	u64 granule = kvm_granule_size(level), phys = data->phys;
> +
> +	if (!kvm_block_mapping_supported(addr, end, phys, level))
> +		return false;
> +
> +	if (kvm_set_valid_leaf_pte(ptep, phys, data->attr, level))
> +		goto out;
> +
> +	kvm_set_invalid_pte(ptep);
> +	kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level);
> +	kvm_set_valid_leaf_pte(ptep, phys, data->attr, level);
> +out:
> +	data->phys += granule;
> +	return true;
> +}
> +
> +static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
> +				     kvm_pte_t *ptep,
> +				     struct stage2_map_data *data)
> +{
> +	if (data->anchor)
> +		return 0;
> +
> +	if (!kvm_block_mapping_supported(addr, end, data->phys, level))
> +		return 0;
> +
> +	kvm_set_invalid_pte(ptep);
> +	kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, 0);
> +	data->anchor = ptep;
> +	return 0;
> +}
> +
> +static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> +				struct stage2_map_data *data)
> +{
> +	kvm_pte_t *childp, pte = *ptep;
> +	struct page *page = virt_to_page(ptep);
> +
> +	if (data->anchor) {
> +		if (kvm_pte_valid(pte))
> +			put_page(page);
> +
> +		return 0;
> +	}
> +
> +	if (stage2_map_walker_try_leaf(addr, end, level, ptep, data))
> +		goto out_get_page;
> +
> +	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
> +		return -EINVAL;
> +
> +	childp = stage2_memcache_alloc_page(data);
> +	if (!childp)
> +		return -ENOMEM;
> +
> +	/*
> +	 * If we've run into an existing block mapping then replace it with
> +	 * a table. Accesses beyond 'end' that fall within the new table
> +	 * will be mapped lazily.
> +	 */
> +	if (kvm_pte_valid(pte)) {
> +		kvm_set_invalid_pte(ptep);
> +		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level);
> +		put_page(page);
> +	}
> +
> +	kvm_set_table_pte(ptep, childp);
> +
> +out_get_page:
> +	get_page(page);
> +	return 0;
> +}
> +
> +static int stage2_map_walk_table_post(u64 addr, u64 end, u32 level,
> +				      kvm_pte_t *ptep,
> +				      struct stage2_map_data *data)
> +{
> +	int ret = 0;
> +
> +	if (!data->anchor)
> +		return 0;
> +
> +	free_page((unsigned long)kvm_pte_follow(*ptep));
> +	put_page(virt_to_page(ptep));
> +
> +	if (data->anchor == ptep) {
> +		data->anchor = NULL;
> +		ret = stage2_map_walk_leaf(addr, end, level, ptep, data);
> +	}
> +
> +	return ret;
> +}
> +

stage2_map_walk_leaf() tries to build the huge (block?) mapping. It then
populate next-level page table if that fails. So it has more than what we
want. I think we might need call to stage2_map_walker_try_leaf() here.
However, there is nothing wrong to me :)

> +static int stage2_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> +			     enum kvm_pgtable_walk_flags flag, void * const arg)
> +{
> +	struct stage2_map_data *data = arg;
> +
> +	switch (flag) {
> +	case KVM_PGTABLE_WALK_TABLE_PRE:
> +		return stage2_map_walk_table_pre(addr, end, level, ptep, data);
> +	case KVM_PGTABLE_WALK_LEAF:
> +		return stage2_map_walk_leaf(addr, end, level, ptep, data);
> +	case KVM_PGTABLE_WALK_TABLE_POST:
> +		return stage2_map_walk_table_post(addr, end, level, ptep, data);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
> +			   u64 phys, enum kvm_pgtable_prot prot,
> +			   struct kvm_mmu_memory_cache *mc)
> +{
> +	int ret;
> +	struct stage2_map_data map_data = {
> +		.phys		= ALIGN_DOWN(phys, PAGE_SIZE),
> +		.mmu		= pgt->mmu,
> +		.memcache	= mc,
> +	};
> +	struct kvm_pgtable_walker walker = {
> +		.cb		= stage2_map_walker,
> +		.flags		= KVM_PGTABLE_WALK_TABLE_PRE |
> +				  KVM_PGTABLE_WALK_LEAF |
> +				  KVM_PGTABLE_WALK_TABLE_POST,
> +		.arg		= &map_data,
> +	};
> +
> +	ret = stage2_map_set_prot_attr(prot, &map_data);
> +	if (ret)
> +		return ret;
> +
> +	ret = kvm_pgtable_walk(pgt, addr, size, &walker);
> +	dsb(ishst);
> +	return ret;
> +}
> +
> +static void stage2_flush_dcache(void *addr, u64 size)
> +{
> +	if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
> +		return;
> +
> +	__flush_dcache_area(addr, size);
> +}
> +
> +static bool stage2_pte_cacheable(kvm_pte_t pte)
> +{
> +	u64 memattr = FIELD_GET(KVM_PTE_LEAF_ATTR_LO_S2_MEMATTR, pte);
> +	return memattr == PAGE_S2_MEMATTR(NORMAL);
> +}
> +
> +static int stage2_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> +			       enum kvm_pgtable_walk_flags flag,
> +			       void * const arg)
> +{
> +	struct kvm_s2_mmu *mmu = arg;
> +	kvm_pte_t pte = *ptep, *childp = NULL;
> +	bool need_flush = false;
> +
> +	if (!kvm_pte_valid(pte))
> +		return 0;
> +
> +	if (kvm_pte_table(pte, level)) {
> +		childp = kvm_pte_follow(pte);
> +
> +		if (page_count(virt_to_page(childp)) != 1)
> +			return 0;
> +	} else if (stage2_pte_cacheable(pte)) {
> +		need_flush = true;
> +	}
> +
> +	/*
> +	 * This is similar to the map() path in that we unmap the entire
> +	 * block entry and rely on the remaining portions being faulted
> +	 * back lazily.
> +	 */
> +	kvm_set_invalid_pte(ptep);
> +	kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, addr, level);
> +	put_page(virt_to_page(ptep));
> +
> +	if (need_flush) {
> +		stage2_flush_dcache(kvm_pte_follow(pte),
> +				    kvm_granule_size(level));
> +	}
> +
> +	if (childp)
> +		free_page((unsigned long)childp);
> +
> +	return 0;
> +}
> +
> +int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
> +{
> +	struct kvm_pgtable_walker walker = {
> +		.cb	= stage2_unmap_walker,
> +		.arg	= pgt->mmu,
> +		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
> +	};
> +
> +	return kvm_pgtable_walk(pgt, addr, size, &walker);
> +}
> +
>   int kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm *kvm)
>   {
>   	size_t pgd_sz;
> 

Thanks,
Gavin


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