Message-ID: <83071e55-cbe4-4786-b60e-d26ce16368b3@arm.com>
Date: Tue, 6 May 2025 14:23:24 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>, Zenghui Yu <yuzenghui@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Joey Gouly <joey.gouly@....com>, Alexandru Elisei
 <alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>,
 Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 Alper Gun <alpergun@...gle.com>, "Aneesh Kumar K . V"
 <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v8 15/43] arm64: RME: Allow VMM to set RIPAS

Hi Steven

On 16/04/2025 14:41, Steven Price wrote:
> Each page within the protected region of the realm guest can be marked
> as either RAM or EMPTY. Allow the VMM to control this before the guest
> has started and provide the equivalent functions to change this (with
> the guest's approval) at runtime.
> 
> When transitioning from RIPAS RAM (1) to RIPAS EMPTY (0) the memory is
> unmapped from the guest and undelegated allowing the memory to be reused
> by the host. When transitioning to RIPAS RAM the actual population of
> the leaf RTTs is done later on stage 2 fault, however it may be
> necessary to allocate additional RTTs to allow the RMM track the RIPAS
> for the requested range.
> 
> When freeing a block mapping it is necessary to temporarily unfold the
> RTT which requires delegating an extra page to the RMM, this page can
> then be recovered once the contents of the block mapping have been
> freed.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> ---
> Changes from v7:
>   * Replace use of "only_shared" with the upstream "attr_filter" field
>     of struct kvm_gfn_range.
>   * Clean up the logic in alloc_delegated_granule() for when to call
>     kvm_account_pgtable_pages().
>   * Rename realm_destroy_protected_granule() to
>     realm_destroy_private_granule() to match the naming elsewhere. Also
>     fix the return codes in the function to be descriptive.
>   * Several other minor changes to names/return codes.
> Changes from v6:
>   * Split the code dealing with the guest triggering a RIPAS change into
>     a separate patch, so this patch is purely for the VMM setting up the
>     RIPAS before the guest first runs.
>   * Drop the useless flags argument from alloc_delegated_granule().
>   * Account RTTs allocated for a guest using kvm_account_pgtable_pages().
>   * Deal with the RMM granule size potentially being smaller than the
>     host's PAGE_SIZE. Although note alloc_delegated_granule() currently
>     still allocates an entire host page for every RMM granule (so wasting
>     memory when PAGE_SIZE>4k).
> Changes from v5:
>   * Adapt to rebasing.
>   * Introduce find_map_level()
>   * Rename some functions to be clearer.
>   * Drop the "spare page" functionality.
> Changes from v2:
>   * {alloc,free}_delegated_page() moved from previous patch to this one.
>   * alloc_delegated_page() now takes a gfp_t flags parameter.
>   * Fix the reference counting of guestmem pages to avoid leaking memory.
>   * Several misc code improvements and extra comments.
> ---
>   arch/arm64/include/asm/kvm_rme.h |   5 +
>   arch/arm64/kvm/mmu.c             |   8 +-
>   arch/arm64/kvm/rme.c             | 384 +++++++++++++++++++++++++++++++
>   3 files changed, 394 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> index 9bcad6ec5dbb..b916db8565a2 100644
> --- a/arch/arm64/include/asm/kvm_rme.h
> +++ b/arch/arm64/include/asm/kvm_rme.h
> @@ -101,6 +101,11 @@ void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits);
>   int kvm_create_rec(struct kvm_vcpu *vcpu);
>   void kvm_destroy_rec(struct kvm_vcpu *vcpu);
>   
> +void kvm_realm_unmap_range(struct kvm *kvm,
> +			   unsigned long ipa,
> +			   unsigned long size,
> +			   bool unmap_private);
> +
>   static inline bool kvm_realm_is_private_address(struct realm *realm,
>   						unsigned long addr)
>   {
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index d80a9d408f71..71c04259e39f 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -323,6 +323,7 @@ static void invalidate_icache_guest_page(void *va, size_t size)
>    * @start: The intermediate physical base address of the range to unmap
>    * @size:  The size of the area to unmap
>    * @may_block: Whether or not we are permitted to block
> + * @only_shared: If true then protected mappings should not be unmapped
>    *
>    * Clear a range of stage-2 mappings, lowering the various ref-counts.  Must
>    * be called while holding mmu_lock (unless for freeing the stage2 pgd before
> @@ -330,7 +331,7 @@ static void invalidate_icache_guest_page(void *va, size_t size)
>    * with things behind our backs.
>    */
>   static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size,
> -				 bool may_block)
> +				 bool may_block, bool only_shared)
>   {
>   	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
>   	phys_addr_t end = start + size;
> @@ -344,7 +345,7 @@ static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64
>   void kvm_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);
> +	__unmap_stage2_range(mmu, start, size, may_block, false);
>   }
>   
>   void kvm_stage2_flush_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_t end)
> @@ -1975,7 +1976,8 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>   
>   	__unmap_stage2_range(&kvm->arch.mmu, range->start << PAGE_SHIFT,
>   			     (range->end - range->start) << PAGE_SHIFT,
> -			     range->may_block);
> +			     range->may_block,
> +			     !(range->attr_filter & KVM_FILTER_PRIVATE));
>   
>   	kvm_nested_s2_unmap(kvm, range->may_block);
>   	return false;
> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> index 1239eb07aca6..33eb793d8bdb 100644
> --- a/arch/arm64/kvm/rme.c
> +++ b/arch/arm64/kvm/rme.c
> @@ -87,6 +87,51 @@ static int get_start_level(struct realm *realm)
>   	return 4 - ((realm->ia_bits - 8) / (RMM_PAGE_SHIFT - 3));
>   }
>   

> +
> +static phys_addr_t alloc_delegated_granule(struct kvm_mmu_memory_cache *mc)
> +{
> +	phys_addr_t phys;
> +	void *virt;
> +
> +	if (mc)
> +		virt = kvm_mmu_memory_cache_alloc(mc);
> +	else
> +		virt = (void *)__get_free_page(GFP_KERNEL_ACCOUNT);
> +
> +	if (!virt)
> +		return PHYS_ADDR_MAX;
> +
> +	phys = virt_to_phys(virt);
> +
> +	if (rmi_granule_delegate(phys)) {
> +		free_page((unsigned long)virt);
> +
> +		return PHYS_ADDR_MAX;
> +	}
> +


> +	kvm_account_pgtable_pages(virt, 1);

Could we delay this to the place where we actually use it ? Otherwise
we may get the accounting wrong, if e.g, free it using
free_delegated_granule() ? Also, the name doesn't suggest that
we are allocating an rtt (though it accepts a memory_cache for rtts).


> +
> +	return phys;
> +}
> +
>   static void free_delegated_granule(phys_addr_t phys)
>   {
>   	if (WARN_ON(rmi_granule_undelegate(phys))) {
> @@ -99,6 +144,154 @@ static void free_delegated_granule(phys_addr_t phys)
>   	free_page((unsigned long)phys_to_virt(phys));
>   }
>   
> +static int realm_rtt_create(struct realm *realm,
> +			    unsigned long addr,
> +			    int level,
> +			    phys_addr_t phys)
> +{
> +	addr = ALIGN_DOWN(addr, rme_rtt_level_mapsize(level - 1));
> +	return rmi_rtt_create(virt_to_phys(realm->rd), phys, addr, level);
> +}
> +
> +static int realm_rtt_fold(struct realm *realm,
> +			  unsigned long addr,
> +			  int level,
> +			  phys_addr_t *rtt_granule)
> +{
> +	unsigned long out_rtt;
> +	int ret;
> +
> +	ret = rmi_rtt_fold(virt_to_phys(realm->rd), addr, level, &out_rtt);

minor nit: Should we align "addr" to level - 1, similar to what we do
for rtt_create, just to be consistent and safer ?

> +
> +	if (RMI_RETURN_STATUS(ret) == RMI_SUCCESS && rtt_granule)
> +		*rtt_granule = out_rtt;
> +
> +	return ret;
> +}
> +
> +static int realm_destroy_private_granule(struct realm *realm,
> +					 unsigned long ipa,
> +					 unsigned long *next_addr,
> +					 phys_addr_t *out_rtt)
> +{
> +	unsigned long rd = virt_to_phys(realm->rd);
> +	unsigned long rtt_addr;
> +	phys_addr_t rtt;
> +	int ret;
> +
> +retry:
> +	ret = rmi_data_destroy(rd, ipa, &rtt_addr, next_addr);
> +	if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT) {
> +		if (*next_addr > ipa)
> +			return 0; /* UNASSIGNED */
> +		rtt = alloc_delegated_granule(NULL);
> +		if (WARN_ON(rtt == PHYS_ADDR_MAX))
> +			return -ENOMEM;
> +		/*
> +		 * ASSIGNED - ipa is mapped as a block, so split. The index
> +		 * from the return code should be 2 otherwise it appears
> +		 * there's a huge page bigger than KVM currently supports
> +		 */
> +		WARN_ON(RMI_RETURN_INDEX(ret) != 2);
> +		ret = realm_rtt_create(realm, ipa, 3, rtt);
> +		if (WARN_ON(ret)) {

Can we race with another thread ? If so, we may need to do an rtt read
to confirm if we are safe to retry and ignore the failure.

> +			free_delegated_granule(rtt);
> +			return -ENXIO;
> +		}
> +		goto retry;
> +	} else if (WARN_ON(ret)) {

minor nit: I am wondering, if we should add a new wrapper for warn_on, 
which also dumps the RTT entry and the operation that caused the WARNING 
? Might be useful to debug and pin point issues. We have several cases
where this might be used.

> +		return -ENXIO;
> +	}
> +
> +	ret = rmi_granule_undelegate(rtt_addr);
> +	if (WARN_ON(ret))
> +		return -ENXIO;
> +
> +	*out_rtt = rtt_addr;
> +
> +	return 0;
> +}
> +
> +static int realm_unmap_private_page(struct realm *realm,
> +				    unsigned long ipa,
> +				    unsigned long *next_addr)
> +{
> +	unsigned long end = ALIGN(ipa + 1, PAGE_SIZE);
> +	unsigned long addr;
> +	phys_addr_t out_rtt = PHYS_ADDR_MAX;
> +	int ret;
> +
> +	for (addr = ipa; addr < end; addr = *next_addr) {
> +		ret = realm_destroy_private_granule(realm, addr, next_addr,
> +						    &out_rtt);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	if (out_rtt != PHYS_ADDR_MAX)
> +		free_page((unsigned long)phys_to_virt(out_rtt));

nit: If this non-4K host, then, we may want to ALIGN_DOWN(out_rtt, 
PAGE_SIZE) ?

> +
> +	return 0;
> +}
> +
> +static void realm_unmap_shared_range(struct kvm *kvm,
> +				     int level,
> +				     unsigned long start,
> +				     unsigned long end)
> +{
> +	struct realm *realm = &kvm->arch.realm;
> +	unsigned long rd = virt_to_phys(realm->rd);
> +	ssize_t map_size = rme_rtt_level_mapsize(level);
> +	unsigned long next_addr, addr;
> +	unsigned long shared_bit = BIT(realm->ia_bits - 1);
> +
> +	if (WARN_ON(level > RMM_RTT_MAX_LEVEL))
> +		return;
> +
> +	start |= shared_bit;
> +	end |= shared_bit;
> +
> +	for (addr = start; addr < end; addr = next_addr) {
> +		unsigned long align_addr = ALIGN(addr, map_size);
> +		int ret;
> +
> +		next_addr = ALIGN(addr + 1, map_size);
> +
> +		if (align_addr != addr || next_addr > end) {
> +			/* Need to recurse deeper */
> +			if (addr < align_addr)
> +				next_addr = align_addr;
> +			realm_unmap_shared_range(kvm, level + 1, addr,
> +						 min(next_addr, end));
> +			continue;
> +		}
> +
> +		ret = rmi_rtt_unmap_unprotected(rd, addr, level, &next_addr);
> +		switch (RMI_RETURN_STATUS(ret)) {
> +		case RMI_SUCCESS:
> +			break;
> +		case RMI_ERROR_RTT:
> +			if (next_addr == addr) {
> +				/*
> +				 * There's a mapping here, but it's not a block
> +				 * mapping, so reset next_addr to the next block
> +				 * boundary and recurse to clear out the pages
> +				 * one level deeper.
> +				 */
> +				next_addr = ALIGN(addr + 1, map_size);
> +				realm_unmap_shared_range(kvm, level + 1, addr,
> +							 next_addr);
> +			}
> +			break;
> +		default:
> +			WARN_ON(1);
> +			return;
> +		}
> +
> +		cond_resched_rwlock_write(&kvm->mmu_lock);
> +	}
> +}
> +
>   /* Calculate the number of s2 root rtts needed */
>   static int realm_num_root_rtts(struct realm *realm)
>   {
> @@ -209,6 +402,40 @@ static int realm_rtt_destroy(struct realm *realm, unsigned long addr,
>   	return ret;
>   }
>   
> +static int realm_create_rtt_levels(struct realm *realm,
> +				   unsigned long ipa,
> +				   int level,
> +				   int max_level,
> +				   struct kvm_mmu_memory_cache *mc)
> +{
> +	if (level == max_level)
> +		return 0;
> +
> +	while (level++ < max_level) {
> +		phys_addr_t rtt = alloc_delegated_granule(mc);
> +		int ret;
> +
> +		if (rtt == PHYS_ADDR_MAX)
> +			return -ENOMEM;
> +
> +		ret = realm_rtt_create(realm, ipa, level, rtt);
> +
> +		if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT &&
> +		    RMI_RETURN_INDEX(ret) == level) {

For the record, as Aneesh pointed out offline, this must be level - 1,
as rtt_create only walks to level - 1.

> +			/* The RTT already exists, continue */
> +			continue;
> +		}
> +		if (ret) {
> +			WARN(1, "Failed to create RTT at level %d: %d\n",
> +			     level, ret);
> +			free_delegated_granule(rtt);
> +			return -ENXIO;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>   static int realm_tear_down_rtt_level(struct realm *realm, int level,
>   				     unsigned long start, unsigned long end)
>   {
> @@ -299,6 +526,61 @@ static int realm_tear_down_rtt_range(struct realm *realm,
>   					 start, end);
>   }
>   
> +/*
> + * Returns 0 on successful fold, a negative value on error, a positive value if
> + * we were not able to fold all tables at this level.
> + */
> +static int realm_fold_rtt_level(struct realm *realm, int level,
> +				unsigned long start, unsigned long end)
> +{
> +	int not_folded = 0;
> +	ssize_t map_size;
> +	unsigned long addr, next_addr;
> +
> +	if (WARN_ON(level > RMM_RTT_MAX_LEVEL))
> +		return -EINVAL;
> +
> +	map_size = rme_rtt_level_mapsize(level - 1);
> +
> +	for (addr = start; addr < end; addr = next_addr) {
> +		phys_addr_t rtt_granule;
> +		int ret;
> +		unsigned long align_addr = ALIGN(addr, map_size);
> +
> +		next_addr = ALIGN(addr + 1, map_size);
> +
> +		ret = realm_rtt_fold(realm, align_addr, level, &rtt_granule);
> +
> +		switch (RMI_RETURN_STATUS(ret)) {
> +		case RMI_SUCCESS:
> +			free_delegated_granule(rtt_granule);
> +			break;
> +		case RMI_ERROR_RTT:
> +			if (level == RMM_RTT_MAX_LEVEL ||
> +			    RMI_RETURN_INDEX(ret) < level) {
> +				not_folded++;
> +				break;
> +			}
> +			/* Recurse a level deeper */
> +			ret = realm_fold_rtt_level(realm,
> +						   level + 1,
> +						   addr,
> +						   next_addr);
> +			if (ret < 0)
> +				return ret;
> +			else if (ret == 0)
> +				/* Try again at this level */
> +				next_addr = addr;
> +			break;
> +		default:
> +			WARN_ON(1);
> +			return -ENXIO;
> +		}
> +	}
> +
> +	return not_folded;
> +}
> +
>   void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits)
>   {
>   	struct realm *realm = &kvm->arch.realm;
> @@ -306,6 +588,96 @@ void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits)
>   	WARN_ON(realm_tear_down_rtt_range(realm, 0, (1UL << ia_bits)));
>   }
>   
> +static void realm_unmap_private_range(struct kvm *kvm,
> +				      unsigned long start,
> +				      unsigned long end)
> +{
> +	struct realm *realm = &kvm->arch.realm;
> +	unsigned long next_addr, addr;
> +	int ret;
> +
> +	for (addr = start; addr < end; addr = next_addr) {
> +		ret = realm_unmap_private_page(realm, addr, &next_addr);
> +
> +		if (ret)
> +			break;

Do we need yielding CPU here, similar to the shared case ? It may be 
difficult (not impossible) to define a check point to do that.


> +	}
> +
> +	realm_fold_rtt_level(realm, get_start_level(realm) + 1,
> +			     start, end);

We don't seem to be reclaiing the RTTs from shared mapping case ?

> +}
> +
> +void kvm_realm_unmap_range(struct kvm *kvm, unsigned long start,
> +			   unsigned long size, bool unmap_private)
> +{
> +	unsigned long end = start + size;
> +	struct realm *realm = &kvm->arch.realm;
> +
> +	end = min(BIT(realm->ia_bits - 1), end);
> +
> +	if (realm->state == REALM_STATE_NONE)
> +		return;
> +
> +	realm_unmap_shared_range(kvm, find_map_level(realm, start, end),
> +				 start, end);
> +	if (unmap_private)
> +		realm_unmap_private_range(kvm, start, end);
> +}
> +
> +static int realm_init_ipa_state(struct realm *realm,
> +				unsigned long ipa,
> +				unsigned long end)
> +{
> +	phys_addr_t rd_phys = virt_to_phys(realm->rd);
> +	int ret;
> +
> +	while (ipa < end) {
> +		unsigned long next;
> +
> +		ret = rmi_rtt_init_ripas(rd_phys, ipa, end, &next);
> +
> +		if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT) {
> +			int err_level = RMI_RETURN_INDEX(ret);
> +			int level = find_map_level(realm, ipa, end);
> +
> +			if (WARN_ON(err_level >= level))

I am wondering if WARN_ON() is required here. A buggy VMM could trigger
the WARN_ON(). (e.g, INIT_IPA after POPULATE, where L3 table is
created.). The only case where it may be worth WARNING is if the level == 3.

Suzuki



> +				return -ENXIO;
> +
> +			ret = realm_create_rtt_levels(realm, ipa,
> +						      err_level,
> +						      level, NULL);
> +			if (ret)
> +				return ret;
> +			/* Retry with the RTT levels in place */
> +			continue;
> +		} else if (WARN_ON(ret)) {
> +			return -ENXIO;
> +		}
> +
> +		ipa = next;
> +	}
> +
> +	return 0;
> +}
> +
> +static int kvm_init_ipa_range_realm(struct kvm *kvm,
> +				    struct arm_rme_init_ripas *args)
> +{
> +	gpa_t addr, end;
> +	struct realm *realm = &kvm->arch.realm;
> +
> +	addr = args->base;
> +	end = addr + args->size;
> +
> +	if (end < addr)
> +		return -EINVAL;
> +
> +	if (kvm_realm_state(kvm) != REALM_STATE_NEW)
> +		return -EPERM;
> +
> +	return realm_init_ipa_state(realm, addr, end);
> +}
> +
>   /* Protects access to rme_vmid_bitmap */
>   static DEFINE_SPINLOCK(rme_vmid_lock);
>   static unsigned long *rme_vmid_bitmap;
> @@ -431,6 +803,18 @@ int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>   	case KVM_CAP_ARM_RME_CREATE_REALM:
>   		r = kvm_create_realm(kvm);
>   		break;
> +	case KVM_CAP_ARM_RME_INIT_RIPAS_REALM: {
> +		struct arm_rme_init_ripas args;
> +		void __user *argp = u64_to_user_ptr(cap->args[1]);
> +
> +		if (copy_from_user(&args, argp, sizeof(args))) {
> +			r = -EFAULT;
> +			break;
> +		}
> +
> +		r = kvm_init_ipa_range_realm(kvm, &args);
> +		break;
> +	}
>   	default:
>   		r = -EINVAL;
>   		break;

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