Re: [RFC PATCH v2 16/26] KVM: arm64: Prepare Hyp memory protection

[Will Deacon <will@kernel.org>]

On Fri, Jan 08, 2021 at 12:15:14PM +0000, Quentin Perret wrote:
> When memory protection is enabled, the Hyp code needs the ability to
> create and manage its own page-table. To do so, introduce a new set of
> hypercalls to initialize Hyp memory protection.
> 
> During the init hcall, the hypervisor runs with the host-provided
> page-table and uses the trivial early page allocator to create its own
> set of page-tables, using a memory pool that was donated by the host.
> Specifically, the hypervisor creates its own mappings for __hyp_text,
> the Hyp memory pool, the __hyp_bss, the portion of hyp_vmemmap
> corresponding to the Hyp pool, among other things. It then jumps back in
> the idmap page, switches to use the newly-created pgd (instead of the
> temporary one provided by the host) and then installs the full-fledged
> buddy allocator which will then be the only one in used from then on.
> 
> Note that for the sake of symplifying the review, this only introduces
> the code doing this operation, without actually being called by anyhing
> yet. This will be done in a subsequent patch, which will introduce the
> necessary host kernel changes.
> 
> Credits to Will for __pkvm_init_switch_pgd.
> 
> Co-authored-by: Will Deacon <will@kernel.org>
> Signed-off-by: Will Deacon <will@kernel.org>
> Signed-off-by: Quentin Perret <qperret@google.com>

[...]

> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index c0450828378b..a0e113734b20 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -100,4 +100,12 @@ void __noreturn hyp_panic(void);
>  void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
>  #endif
>  
> +#ifdef __KVM_NVHE_HYPERVISOR__
> +void __pkvm_init_switch_pgd(phys_addr_t phys, unsigned long size,
> +			    phys_addr_t pgd, void *sp, void *cont_fn);
> +int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
> +		unsigned long *per_cpu_base);
> +void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);
> +#endif
> +
>  #endif /* __ARM64_KVM_HYP_H__ */
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index 43f3a1d6e92d..366d837f0d39 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -113,6 +113,25 @@ KVM_NVHE_ALIAS_HYP(__memcpy, __pi_memcpy);
>  KVM_NVHE_ALIAS_HYP(__memset, __pi_memset);
>  #endif
>  
> +/* Hypevisor VA size */

typo: Hypervisor

> +KVM_NVHE_ALIAS(hyp_va_bits);
> +
> +/* Kernel memory sections */
> +KVM_NVHE_ALIAS(__start_rodata);
> +KVM_NVHE_ALIAS(__end_rodata);
> +KVM_NVHE_ALIAS(__bss_start);
> +KVM_NVHE_ALIAS(__bss_stop);
> +
> +/* Hyp memory sections */
> +KVM_NVHE_ALIAS(__hyp_idmap_text_start);
> +KVM_NVHE_ALIAS(__hyp_idmap_text_end);
> +KVM_NVHE_ALIAS(__hyp_text_start);
> +KVM_NVHE_ALIAS(__hyp_text_end);
> +KVM_NVHE_ALIAS(__hyp_data_ro_after_init_start);
> +KVM_NVHE_ALIAS(__hyp_data_ro_after_init_end);
> +KVM_NVHE_ALIAS(__hyp_bss_start);
> +KVM_NVHE_ALIAS(__hyp_bss_end);
> +
>  #endif /* CONFIG_KVM */
>  
>  #endif /* __ARM64_KERNEL_IMAGE_VARS_H */
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 687598e41b21..b726332eec49 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -10,4 +10,4 @@ subdir-ccflags-y := -I$(incdir)				\
>  		    -DDISABLE_BRANCH_PROFILING		\
>  		    $(DISABLE_STACKLEAK_PLUGIN)
>  
> -obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
> +obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o reserved_mem.o
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/memory.h b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> index ed47674bc988..c8af6fe87bfb 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/memory.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> @@ -6,6 +6,12 @@
>  
>  #include <linux/types.h>
>  
> +#define HYP_MEMBLOCK_REGIONS 128
> +struct hyp_memblock_region {
> +	phys_addr_t start;
> +	phys_addr_t end;
> +};
> +
>  struct hyp_pool;
>  struct hyp_page {
>  	unsigned int refcount;
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> new file mode 100644
> index 000000000000..f0cc09b127a5
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> @@ -0,0 +1,79 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __KVM_HYP_MM_H
> +#define __KVM_HYP_MM_H
> +
> +#include <asm/kvm_pgtable.h>
> +#include <asm/spectre.h>
> +#include <linux/types.h>
> +
> +#include <nvhe/memory.h>
> +#include <nvhe/spinlock.h>
> +
> +extern struct hyp_memblock_region kvm_nvhe_sym(hyp_memory)[];
> +extern int kvm_nvhe_sym(hyp_memblock_nr);
> +extern struct kvm_pgtable pkvm_pgtable;
> +extern hyp_spinlock_t pkvm_pgd_lock;
> +extern struct hyp_pool hpool;
> +extern u64 __io_map_base;
> +extern u32 hyp_va_bits;
> +
> +int hyp_create_idmap(void);
> +int hyp_map_vectors(void);
> +int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back);
> +int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot);
> +int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
> +int __pkvm_create_mappings(unsigned long start, unsigned long size,
> +			   unsigned long phys, unsigned long prot);
> +unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
> +					    unsigned long prot);
> +
> +static inline void hyp_vmemmap_range(phys_addr_t phys, unsigned long size,
> +				     unsigned long *start, unsigned long *end)
> +{
> +	unsigned long nr_pages = size >> PAGE_SHIFT;
> +	struct hyp_page *p = hyp_phys_to_page(phys);
> +
> +	*start = (unsigned long)p;
> +	*end = *start + nr_pages * sizeof(struct hyp_page);
> +	*start = ALIGN_DOWN(*start, PAGE_SIZE);
> +	*end = ALIGN(*end, PAGE_SIZE);
> +}
> +
> +static inline unsigned long __hyp_pgtable_max_pages(unsigned long nr_pages)
> +{
> +	unsigned long total = 0, i;
> +
> +	/* Provision the worst case scenario with 4 levels of page-table */
> +	for (i = 0; i < 4; i++) {

Looks like you want KVM_PGTABLE_MAX_LEVELS, so maybe move that into a
header?

> +		nr_pages = DIV_ROUND_UP(nr_pages, PTRS_PER_PTE);
> +		total += nr_pages;
> +	}

... that said, I'm not sure this needs to iterate at all. What exactly are
you trying to compute?

> +
> +	return total;
> +}
> +
> +static inline unsigned long hyp_s1_pgtable_size(void)
> +{
> +	struct hyp_memblock_region *reg;
> +	unsigned long nr_pages, res = 0;
> +	int i;
> +
> +	if (kvm_nvhe_sym(hyp_memblock_nr) <= 0)
> +		return 0;

It's a bit grotty having this be signed. Why do we need to encode the error
case differently from the 0 case?

> +
> +	for (i = 0; i < kvm_nvhe_sym(hyp_memblock_nr); i++) {
> +		reg = &kvm_nvhe_sym(hyp_memory)[i];

You could declare reg in the loop body.

> +		nr_pages = (reg->end - reg->start) >> PAGE_SHIFT;
> +		nr_pages = __hyp_pgtable_max_pages(nr_pages);

Maybe it would make more sense for __hyp_pgtable_max_pages to take the
size in bytes rather than pages, since most callers seem to have to do the
conversion?

> +		res += nr_pages << PAGE_SHIFT;
> +	}
> +
> +	/* Allow 1 GiB for private mappings */
> +	nr_pages = (1 << 30) >> PAGE_SHIFT;

SZ_1G >> PAGE_SHIFT

> +	nr_pages = __hyp_pgtable_max_pages(nr_pages);
> +	res += nr_pages << PAGE_SHIFT;
> +
> +	return res;

Might make more sense to keep res in pages until here, then just shift when
returning.

> +}
> +
> +#endif /* __KVM_HYP_MM_H */
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index 72cfe53f106f..d7381a503182 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -11,9 +11,9 @@ lib-objs := $(addprefix ../../../lib/, $(lib-objs))
>  
>  obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
>  	 hyp-main.o hyp-smp.o psci-relay.o early_alloc.o stub.o page_alloc.o \
> -	 cache.o cpufeature.o
> +	 cache.o cpufeature.o setup.o mm.o
>  obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
> -	 ../fpsimd.o ../hyp-entry.o ../exception.o
> +	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
>  obj-y += $(lib-objs)
>  
>  ##
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> index 31b060a44045..ad943966c39f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
> @@ -251,4 +251,35 @@ alternative_else_nop_endif
>  
>  SYM_CODE_END(__kvm_handle_stub_hvc)
>  
> +SYM_FUNC_START(__pkvm_init_switch_pgd)
> +	/* Turn the MMU off */
> +	pre_disable_mmu_workaround
> +	mrs	x2, sctlr_el2
> +	bic	x3, x2, #SCTLR_ELx_M
> +	msr	sctlr_el2, x3
> +	isb
> +
> +	tlbi	alle2
> +
> +	/* Install the new pgtables */
> +	ldr	x3, [x0, #NVHE_INIT_PGD_PA]
> +	phys_to_ttbr x4, x3
> +alternative_if ARM64_HAS_CNP
> +	orr	x4, x4, #TTBR_CNP_BIT
> +alternative_else_nop_endif
> +	msr	ttbr0_el2, x4
> +
> +	/* Set the new stack pointer */
> +	ldr	x0, [x0, #NVHE_INIT_STACK_HYP_VA]
> +	mov	sp, x0
> +
> +	/* And turn the MMU back on! */
> +	dsb	nsh
> +	isb
> +	msr	sctlr_el2, x2
> +	ic	iallu
> +	isb
> +	ret	x1
> +SYM_FUNC_END(__pkvm_init_switch_pgd)
> +
>  	.popsection
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index a906f9e2ff34..3075f117651c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -6,12 +6,14 @@
>  
>  #include <hyp/switch.h>
>  
> +#include <asm/pgtable-types.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_emulate.h>
>  #include <asm/kvm_host.h>
>  #include <asm/kvm_hyp.h>
>  #include <asm/kvm_mmu.h>
>  
> +#include <nvhe/mm.h>
>  #include <nvhe/trap_handler.h>
>  
>  DEFINE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> @@ -106,6 +108,42 @@ static void handle___vgic_v3_restore_aprs(struct kvm_cpu_context *host_ctxt)
>  	__vgic_v3_restore_aprs(kern_hyp_va(cpu_if));
>  }
>  
> +static void handle___pkvm_init(struct kvm_cpu_context *host_ctxt)
> +{
> +	DECLARE_REG(phys_addr_t, phys, host_ctxt, 1);
> +	DECLARE_REG(unsigned long, size, host_ctxt, 2);
> +	DECLARE_REG(unsigned long, nr_cpus, host_ctxt, 3);
> +	DECLARE_REG(unsigned long *, per_cpu_base, host_ctxt, 4);
> +
> +	cpu_reg(host_ctxt, 1) = __pkvm_init(phys, size, nr_cpus, per_cpu_base);

__pkvm_init() doesn't return, so I think this assignment back into host_ctxt
is confusing.

Also, I wonder if these bare numbers would be better hidden behind, e.g.

 #define DECLARE_ARG0(...)	DECLARE_REG(__VA_ARGS__, 1)
 ...
 #define DECLARE_RET(...)	DECLARE_REG(__VA_ARGS__, 1)

but it's cosmetic, so no need to change your patch. Just worried about
off-by-1s causing interesting behaviour!

> +
> +static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt)
> +{
> +	DECLARE_REG(enum arm64_hyp_spectre_vector, slot, host_ctxt, 1);
> +
> +	cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot);
> +}
> +
> +static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt)
> +{
> +	DECLARE_REG(unsigned long, start, host_ctxt, 1);
> +	DECLARE_REG(unsigned long, size, host_ctxt, 2);
> +	DECLARE_REG(unsigned long, phys, host_ctxt, 3);
> +	DECLARE_REG(unsigned long, prot, host_ctxt, 4);
> +
> +	cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot);
> +}
> +
> +static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt)
> +{
> +	DECLARE_REG(phys_addr_t, phys, host_ctxt, 1);
> +	DECLARE_REG(size_t, size, host_ctxt, 2);

Why the size_t vs unsigned long discrepancy with pkvm_create_mappings?
Same with phys_addr_t, although that one probably doesn't matter.

Also, the pgtable API uses an enum type for the prot bits.

> +	DECLARE_REG(unsigned long, prot, host_ctxt, 3);
> +
> +	cpu_reg(host_ctxt, 1) = __pkvm_create_private_mapping(phys, size, prot);
> +}
> +
>  typedef void (*hcall_t)(struct kvm_cpu_context *);
>  
>  #define HANDLE_FUNC(x)	[__KVM_HOST_SMCCC_FUNC_##x] = kimg_fn_ptr(handle_##x)
> @@ -125,6 +163,10 @@ static const hcall_t *host_hcall[] = {
>  	HANDLE_FUNC(__kvm_get_mdcr_el2),
>  	HANDLE_FUNC(__vgic_v3_save_aprs),
>  	HANDLE_FUNC(__vgic_v3_restore_aprs),
> +	HANDLE_FUNC(__pkvm_init),
> +	HANDLE_FUNC(__pkvm_cpu_set_vector),
> +	HANDLE_FUNC(__pkvm_create_mappings),
> +	HANDLE_FUNC(__pkvm_create_private_mapping),
>  };
>  
>  static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
> diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
> new file mode 100644
> index 000000000000..f3481646a94e
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/mm.c
> @@ -0,0 +1,174 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 Google LLC
> + * Author: Quentin Perret <qperret@google.com>
> + */
> +
> +#include <linux/kvm_host.h>
> +#include <asm/kvm_hyp.h>
> +#include <asm/kvm_mmu.h>
> +#include <asm/kvm_pgtable.h>
> +#include <asm/spectre.h>
> +
> +#include <nvhe/early_alloc.h>
> +#include <nvhe/gfp.h>
> +#include <nvhe/memory.h>
> +#include <nvhe/mm.h>
> +#include <nvhe/spinlock.h>
> +
> +struct kvm_pgtable pkvm_pgtable;
> +hyp_spinlock_t pkvm_pgd_lock;
> +u64 __io_map_base;
> +
> +struct hyp_memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS];
> +int hyp_memblock_nr;
> +
> +int __pkvm_create_mappings(unsigned long start, unsigned long size,
> +			  unsigned long phys, unsigned long prot)
> +{
> +	int err;
> +
> +	hyp_spin_lock(&pkvm_pgd_lock);
> +	err = kvm_pgtable_hyp_map(&pkvm_pgtable, start, size, phys, prot);
> +	hyp_spin_unlock(&pkvm_pgd_lock);
> +
> +	return err;
> +}
> +
> +unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
> +					   unsigned long prot)
> +{
> +	unsigned long addr;
> +	int ret;
> +
> +	hyp_spin_lock(&pkvm_pgd_lock);
> +
> +	size = PAGE_ALIGN(size + offset_in_page(phys));

It might just be simpler to require page-aligned size and phys in the
caller. At least, for the vectors that should be straightforward because
I think they're guaranteed not to span a page boundary.

> +	addr = __io_map_base;
> +	__io_map_base += size;
> +
> +	/* Are we overflowing on the vmemmap ? */
> +	if (__io_map_base > __hyp_vmemmap) {
> +		__io_map_base -= size;
> +		addr = 0;

Can we use ERR_PTR(), or does that fail miserably at EL2?

> +		goto out;
> +	}
> +
> +	ret = kvm_pgtable_hyp_map(&pkvm_pgtable, addr, size, phys, prot);
> +	if (ret) {
> +		addr = 0;
> +		goto out;
> +	}
> +
> +	addr = addr + offset_in_page(phys);
> +out:
> +	hyp_spin_unlock(&pkvm_pgd_lock);
> +
> +	return addr;
> +}

[...]

> +static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
> +				 unsigned long *per_cpu_base)
> +{
> +	void *start, *end, *virt = hyp_phys_to_virt(phys);
> +	int ret, i;
> +
> +	/* Recreate the hyp page-table using the early page allocator */
> +	hyp_early_alloc_init(hyp_pgt_base, hyp_s1_pgtable_size());
> +	ret = kvm_pgtable_hyp_init(&pkvm_pgtable, hyp_va_bits,
> +				   &hyp_early_alloc_mm_ops);
> +	if (ret)
> +		return ret;
> +
> +	ret = hyp_create_idmap();
> +	if (ret)
> +		return ret;
> +
> +	ret = hyp_map_vectors();
> +	if (ret)
> +		return ret;
> +
> +	ret = hyp_back_vmemmap(phys, size, hyp_virt_to_phys(vmemmap_base));
> +	if (ret)
> +		return ret;
> +
> +	ret = pkvm_create_mappings(hyp_symbol_addr(__hyp_text_start),
> +				  hyp_symbol_addr(__hyp_text_end),
> +				  PAGE_HYP_EXEC);
> +	if (ret)
> +		return ret;
> +
> +	ret = pkvm_create_mappings(hyp_symbol_addr(__start_rodata),
> +				   hyp_symbol_addr(__end_rodata), PAGE_HYP_RO);
> +	if (ret)
> +		return ret;
> +
> +	ret = pkvm_create_mappings(hyp_symbol_addr(__hyp_data_ro_after_init_start),
> +				   hyp_symbol_addr(__hyp_data_ro_after_init_end),
> +				   PAGE_HYP_RO);
> +	if (ret)
> +		return ret;
> +
> +	ret = pkvm_create_mappings(hyp_symbol_addr(__bss_start),

__hyp_bss_start

> +				   hyp_symbol_addr(__hyp_bss_end), PAGE_HYP);
> +	if (ret)
> +		return ret;
> +
> +	ret = pkvm_create_mappings(hyp_symbol_addr(__hyp_bss_end),
> +				   hyp_symbol_addr(__bss_stop), PAGE_HYP_RO);
> +	if (ret)
> +		return ret;
> +
> +	ret = pkvm_create_mappings(virt, virt + size - 1, PAGE_HYP);

Why is the range inclusive here?

> +	if (ret)
> +		return ret;
> +
> +	for (i = 0; i < hyp_nr_cpus; i++) {
> +		start = (void *)kern_hyp_va(per_cpu_base[i]);
> +		end = start + PAGE_ALIGN(hyp_percpu_size);
> +		ret = pkvm_create_mappings(start, end, PAGE_HYP);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void update_nvhe_init_params(void)
> +{
> +	struct kvm_nvhe_init_params *params;
> +	unsigned long i, stack;
> +
> +	for (i = 0; i < hyp_nr_cpus; i++) {
> +		stack = (unsigned long)stacks_base + (i << PAGE_SHIFT);
> +		params = per_cpu_ptr(&kvm_init_params, i);
> +		params->stack_hyp_va = stack + PAGE_SIZE;
> +		params->pgd_pa = __hyp_pa(pkvm_pgtable.pgd);
> +		__flush_dcache_area(params, sizeof(*params));
> +	}
> +}
> +
> +static void *hyp_zalloc_hyp_page(void *arg)
> +{
> +	return hyp_alloc_pages(&hpool, HYP_GFP_ZERO, 0);
> +}
> +
> +void __noreturn __pkvm_init_finalise(void)
> +{
> +	struct kvm_host_data *host_data = this_cpu_ptr(&kvm_host_data);
> +	struct kvm_cpu_context *host_ctxt = &host_data->host_ctxt;
> +	unsigned long nr_pages, used_pages;
> +	int ret;
> +
> +	/* Now that the vmemmap is backed, install the full-fledged allocator */
> +	nr_pages = hyp_s1_pgtable_size() >> PAGE_SHIFT;
> +	used_pages = hyp_early_alloc_nr_pages();
> +	ret = hyp_pool_init(&hpool, __hyp_pa(hyp_pgt_base), nr_pages, used_pages);
> +	if (ret)
> +		goto out;
> +
> +	pkvm_pgtable_mm_ops.zalloc_page = hyp_zalloc_hyp_page;
> +	pkvm_pgtable_mm_ops.phys_to_virt = hyp_phys_to_virt;
> +	pkvm_pgtable_mm_ops.virt_to_phys = hyp_virt_to_phys;
> +	pkvm_pgtable_mm_ops.get_page = hyp_get_page;
> +	pkvm_pgtable_mm_ops.put_page = hyp_put_page;
> +	pkvm_pgtable.mm_ops = &pkvm_pgtable_mm_ops;
> +
> +out:
> +	host_ctxt->regs.regs[0] = SMCCC_RET_SUCCESS;
> +	host_ctxt->regs.regs[1] = ret;

Use the cpu_reg() helper for these?

> +
> +	__host_enter(host_ctxt);
> +}
> +
> +int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long nr_cpus,
> +		unsigned long *per_cpu_base)
> +{
> +	struct kvm_nvhe_init_params *params;
> +	void *virt = hyp_phys_to_virt(phys);
> +	void (*fn)(phys_addr_t params_pa, void *finalize_fn_va);
> +	int ret;
> +
> +	if (phys % PAGE_SIZE || size % PAGE_SIZE || (u64)virt % PAGE_SIZE)
> +		return -EINVAL;
> +
> +	hyp_spin_lock_init(&pkvm_pgd_lock);
> +	hyp_nr_cpus = nr_cpus;
> +
> +	ret = divide_memory_pool(virt, size);
> +	if (ret)
> +		return ret;
> +
> +	ret = recreate_hyp_mappings(phys, size, per_cpu_base);
> +	if (ret)
> +		return ret;
> +
> +	update_nvhe_init_params();
> +
> +	/* Jump in the idmap page to switch to the new page-tables */
> +	params = this_cpu_ptr(&kvm_init_params);
> +	fn = (typeof(fn))__hyp_pa(hyp_symbol_addr(__pkvm_init_switch_pgd));
> +	fn(__hyp_pa(params), hyp_symbol_addr(__pkvm_init_finalise));
> +
> +	unreachable();
> +}
> diff --git a/arch/arm64/kvm/hyp/reserved_mem.c b/arch/arm64/kvm/hyp/reserved_mem.c
> new file mode 100644
> index 000000000000..32f648992835
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/reserved_mem.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2020 - Google LLC
> + * Author: Quentin Perret <qperret@google.com>
> + */
> +
> +#include <linux/kvm_host.h>
> +#include <linux/memblock.h>
> +#include <linux/sort.h>
> +
> +#include <asm/kvm_host.h>
> +
> +#include <nvhe/memory.h>
> +#include <nvhe/mm.h>
> +
> +phys_addr_t hyp_mem_base;
> +phys_addr_t hyp_mem_size;
> +
> +int __init early_init_dt_add_memory_hyp(u64 base, u64 size)
> +{
> +	struct hyp_memblock_region *reg;
> +
> +	if (kvm_nvhe_sym(hyp_memblock_nr) >= HYP_MEMBLOCK_REGIONS)
> +		kvm_nvhe_sym(hyp_memblock_nr) = -1;
> +
> +	if (kvm_nvhe_sym(hyp_memblock_nr) < 0)
> +		return -ENOMEM;
> +
> +	reg = kvm_nvhe_sym(hyp_memory);
> +	reg[kvm_nvhe_sym(hyp_memblock_nr)].start = base;
> +	reg[kvm_nvhe_sym(hyp_memblock_nr)].end = base + size;
> +	kvm_nvhe_sym(hyp_memblock_nr)++;
> +
> +	return 0;
> +}

This isn't called by anything in this patch afaict, so it's a bit tricky to
review, especially as I was trying to see how it interacts with
kvm_hyp_reserve(), which reads hyp_memblock_nr.

> +
> +static int cmp_hyp_memblock(const void *p1, const void *p2)
> +{
> +	const struct hyp_memblock_region *r1 = p1;
> +	const struct hyp_memblock_region *r2 = p2;
> +
> +	return r1->start < r2->start ? -1 : (r1->start > r2->start);
> +}
> +
> +static void __init sort_memblock_regions(void)
> +{
> +	sort(kvm_nvhe_sym(hyp_memory),
> +	     kvm_nvhe_sym(hyp_memblock_nr),
> +	     sizeof(struct hyp_memblock_region),
> +	     cmp_hyp_memblock,
> +	     NULL);
> +}
> +
> +void __init kvm_hyp_reserve(void)
> +{
> +	u64 nr_pages, prev;
> +
> +	if (!is_hyp_mode_available() || is_kernel_in_hyp_mode())
> +		return;
> +
> +	if (kvm_get_mode() != KVM_MODE_PROTECTED)
> +		return;
> +
> +	if (kvm_nvhe_sym(hyp_memblock_nr) < 0) {
> +		kvm_err("Failed to register hyp memblocks\n");
> +		return;
> +	}
> +
> +	sort_memblock_regions();
> +
> +	/*
> +	 * We don't know the number of possible CPUs yet, so allocate for the
> +	 * worst case.
> +	 */
> +	hyp_mem_size += NR_CPUS << PAGE_SHIFT;

There was a recent patch bumping NR_CPUs to 512, so this would be 32MB
with 64k pages. Is it possible to return memory to the host later on once
we have a better handle on the number of CPUs in the system?

> +	hyp_mem_size += hyp_s1_pgtable_size();
> +
> +	/*
> +	 * The hyp_vmemmap needs to be backed by pages, but these pages
> +	 * themselves need to be present in the vmemmap, so compute the number
> +	 * of pages needed by looking for a fixed point.
> +	 */
> +	nr_pages = 0;
> +	do {
> +		prev = nr_pages;
> +		nr_pages = (hyp_mem_size >> PAGE_SHIFT) + prev;
> +		nr_pages = DIV_ROUND_UP(nr_pages * sizeof(struct hyp_page), PAGE_SIZE);
> +		nr_pages += __hyp_pgtable_max_pages(nr_pages);
> +	} while (nr_pages != prev);
> +	hyp_mem_size += nr_pages << PAGE_SHIFT;
> +
> +	hyp_mem_base = memblock_find_in_range(0, memblock_end_of_DRAM(),
> +					      hyp_mem_size, SZ_2M);

Why SZ_2M? Guessing you might mean PMD_SIZE, although then we will probably
want to retry with smaller alignment if the allocation fails as this can
again be large with e.g. 64k pages.

> +	if (!hyp_mem_base) {
> +		kvm_err("Failed to reserve hyp memory\n");
> +		return;
> +	}
> +	memblock_reserve(hyp_mem_base, hyp_mem_size);
> +
> +	kvm_info("Reserved %lld MiB at 0x%llx\n", hyp_mem_size >> 20,
> +		 hyp_mem_base);
> +}
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 278e163beda4..3cf9397dabdb 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1264,10 +1264,10 @@ static struct kvm_pgtable_mm_ops kvm_hyp_mm_ops = {
>  	.virt_to_phys		= kvm_host_pa,
>  };
>  
> +u32 hyp_va_bits;

Perhaps it would be better to pass this to __pkvm_init() instead of making
it global?

Will