[PATCH v4 0/3] Enforce host page-size alignment for shared buffers

[PATCH v4 0/3] Enforce host page-size alignment for shared buffers

[Aneesh Kumar K.V (Arm)]

Hi all,

This patch series addresses alignment requirements for buffers shared between
private-memory guests and the host.

When running private-memory guests, the guest kernel must apply additional
constraints when allocating buffers that are shared with the hypervisor. These
shared buffers are also accessed by the host kernel and therefore must be
aligned to the host’s page size.

Architectures such as Arm can tolerate realm physical address space PFNs being
mapped as shared memory, as incorrect accesses are detected and reported as GPC
faults. However, relying on this mechanism alone is unsafe and can still lead to
kernel crashes.

This is particularly likely when guest_memfd allocations are mmapped and
accessed from userspace. Once exposed to userspace, it is not possible to
guarantee that applications will only access the intended 4K shared region
rather than the full 64K page mapped into their address space. Such userspace
addresses may also be passed back into the kernel and accessed via the linear
map, potentially resulting in a GPC fault and a kernel crash.

To address this, the series introduces a new helpers,
mem_decrypt_granule_size() and mem_decrypt_align(), which allows callers to
enforce the required alignment for shared buffers.

Changes from v3:
https://lore.kernel.org/all/20260309102625.2315725-1-aneesh.kumar@kernel.org
* Fix build error reported by kernel test robot <lkp@intel.com>

Changes from v2:
https://lore.kernel.org/all/20251221160920.297689-1-aneesh.kumar@kernel.org
* Rebase to latest kernel
* Consider swiotlb always decrypted and don't align when allocating from swiotlb.

Changes from v1:
* Rename the helper to mem_encrypt_align
* Improve the commit message
* Handle DMA allocations from contiguous memory
* Handle DMA allocations from the pool
* swiotlb is still considered unencrypted. Support for an encrypted swiotlb pool
  is left as TODO and is independent of this series.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Will Deacon <will@kernel.org>

Aneesh Kumar K.V (Arm) (3):
  dma-direct: swiotlb: handle swiotlb alloc/free outside
    __dma_direct_alloc_pages
  swiotlb: dma: its: Enforce host page-size alignment for shared buffers
  coco: guest: arm64: Query host IPA-change alignment via RHI

 arch/arm64/include/asm/mem_encrypt.h |  3 ++
 arch/arm64/include/asm/rhi.h         | 24 ++++++++++++
 arch/arm64/include/asm/rsi.h         |  2 +
 arch/arm64/include/asm/rsi_cmds.h    | 10 +++++
 arch/arm64/include/asm/rsi_smc.h     |  7 ++++
 arch/arm64/kernel/Makefile           |  2 +-
 arch/arm64/kernel/rhi.c              | 54 ++++++++++++++++++++++++++
 arch/arm64/kernel/rsi.c              | 13 +++++++
 arch/arm64/mm/mem_encrypt.c          | 27 +++++++++++--
 drivers/irqchip/irq-gic-v3-its.c     | 20 ++++++----
 include/linux/mem_encrypt.h          | 14 +++++++
 kernel/dma/contiguous.c              | 10 +++++
 kernel/dma/direct.c                  | 58 ++++++++++++++++++++++++----
 kernel/dma/pool.c                    |  4 +-
 kernel/dma/swiotlb.c                 | 21 ++++++----
 15 files changed, 240 insertions(+), 29 deletions(-)
 create mode 100644 arch/arm64/include/asm/rhi.h
 create mode 100644 arch/arm64/kernel/rhi.c

-- 
2.43.0

[PATCH v4 1/3] dma-direct: swiotlb: handle swiotlb alloc/free outside __dma_direct_alloc_pages

[Aneesh Kumar K.V (Arm)]

Move swiotlb allocation out of __dma_direct_alloc_pages() and handle it in
dma_direct_alloc() / dma_direct_alloc_pages().

This is needed for follow-up changes that align shared decrypted buffers to
hypervisor page size. swiotlb pool memory is decrypted as a whole and does
not need per-allocation alignment handling.

swiotlb backing pages are already mapped decrypted by
swiotlb_update_mem_attributes() and rmem_swiotlb_device_init(), so
dma-direct should not call dma_set_decrypted() on allocation nor
dma_set_encrypted() on free for swiotlb-backed memory.

Update alloc/free paths to detect swiotlb-backed pages and skip
encrypt/decrypt transitions for those paths. Keep the existing highmem
rejection in dma_direct_alloc_pages() for swiotlb allocations.

Only for "restricted-dma-pool", we currently set `for_alloc = true`, while
rmem_swiotlb_device_init() decrypts the whole pool up front. This pool is
typically used together with "shared-dma-pool", where the shared region is
accessed after remap/ioremap and the returned address is suitable for
decrypted memory access. So existing code paths remain valid.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 kernel/dma/direct.c | 44 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8f43a930716d..c2a43e4ef902 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -125,9 +125,6 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
 
 	WARN_ON_ONCE(!PAGE_ALIGNED(size));
 
-	if (is_swiotlb_for_alloc(dev))
-		return dma_direct_alloc_swiotlb(dev, size);
-
 	gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit);
 	page = dma_alloc_contiguous(dev, size, gfp);
 	if (page) {
@@ -204,6 +201,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
 {
 	bool remap = false, set_uncached = false;
+	bool mark_mem_decrypt = true;
 	struct page *page;
 	void *ret;
 
@@ -250,11 +248,21 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 	    dma_direct_use_pool(dev, gfp))
 		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 
+	if (is_swiotlb_for_alloc(dev)) {
+		page = dma_direct_alloc_swiotlb(dev, size);
+		if (page) {
+			mark_mem_decrypt = false;
+			goto setup_page;
+		}
+		return NULL;
+	}
+
 	/* we always manually zero the memory once we are done */
 	page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
 	if (!page)
 		return NULL;
 
+setup_page:
 	/*
 	 * dma_alloc_contiguous can return highmem pages depending on a
 	 * combination the cma= arguments and per-arch setup.  These need to be
@@ -281,7 +289,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 			goto out_free_pages;
 	} else {
 		ret = page_address(page);
-		if (dma_set_decrypted(dev, ret, size))
+		if (mark_mem_decrypt && dma_set_decrypted(dev, ret, size))
 			goto out_leak_pages;
 	}
 
@@ -298,7 +306,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 	return ret;
 
 out_encrypt_pages:
-	if (dma_set_encrypted(dev, page_address(page), size))
+	if (mark_mem_decrypt && dma_set_encrypted(dev, page_address(page), size))
 		return NULL;
 out_free_pages:
 	__dma_direct_free_pages(dev, page, size);
@@ -310,6 +318,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 void dma_direct_free(struct device *dev, size_t size,
 		void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
 {
+	bool mark_mem_encrypted = true;
 	unsigned int page_order = get_order(size);
 
 	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
@@ -338,12 +347,15 @@ void dma_direct_free(struct device *dev, size_t size,
 	    dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
 		return;
 
+	if (swiotlb_find_pool(dev, dma_to_phys(dev, dma_addr)))
+		mark_mem_encrypted = false;
+
 	if (is_vmalloc_addr(cpu_addr)) {
 		vunmap(cpu_addr);
 	} else {
 		if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
 			arch_dma_clear_uncached(cpu_addr, size);
-		if (dma_set_encrypted(dev, cpu_addr, size))
+		if (mark_mem_encrypted && dma_set_encrypted(dev, cpu_addr, size))
 			return;
 	}
 
@@ -359,6 +371,19 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
 	if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
 		return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
 
+	if (is_swiotlb_for_alloc(dev)) {
+		page = dma_direct_alloc_swiotlb(dev, size);
+		if (!page)
+			return NULL;
+
+		if (PageHighMem(page)) {
+			swiotlb_free(dev, page, size);
+			return NULL;
+		}
+		ret = page_address(page);
+		goto setup_page;
+	}
+
 	page = __dma_direct_alloc_pages(dev, size, gfp, false);
 	if (!page)
 		return NULL;
@@ -366,6 +391,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
 	ret = page_address(page);
 	if (dma_set_decrypted(dev, ret, size))
 		goto out_leak_pages;
+setup_page:
 	memset(ret, 0, size);
 	*dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
 	return page;
@@ -378,13 +404,17 @@ void dma_direct_free_pages(struct device *dev, size_t size,
 		enum dma_data_direction dir)
 {
 	void *vaddr = page_address(page);
+	bool mark_mem_encrypted = true;
 
 	/* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
 	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
 	    dma_free_from_pool(dev, vaddr, size))
 		return;
 
-	if (dma_set_encrypted(dev, vaddr, size))
+	if (swiotlb_find_pool(dev, page_to_phys(page)))
+		mark_mem_encrypted = false;
+
+	if (mark_mem_encrypted && dma_set_encrypted(dev, vaddr, size))
 		return;
 	__dma_direct_free_pages(dev, page, size);
 }
-- 
2.43.0

[PATCH v4 2/3] swiotlb: dma: its: Enforce host page-size alignment for shared buffers

[Aneesh Kumar K.V (Arm)]

When running private-memory guests, the guest kernel must apply additional
constraints when allocating buffers that are shared with the hypervisor.

These shared buffers are also accessed by the host kernel and therefore
must be aligned to the host’s page size, and have a size that is a multiple
of the host page size.

On non-secure hosts, set_guest_memory_attributes() tracks memory at the
host PAGE_SIZE granularity. This creates a mismatch when the guest applies
attributes at 4K boundaries while the host uses 64K pages. In such cases,
set_guest_memory_attributes() call returns -EINVAL, preventing the
conversion of memory regions from private to shared.

Architectures such as Arm can tolerate realm physical address space
(protected memory) PFNs being mapped as shared memory, as incorrect
accesses are detected and reported as GPC faults. However, relying on this
mechanism is unsafe and can still lead to kernel crashes.

This is particularly likely when guest_memfd allocations are mmapped and
accessed from userspace. Once exposed to userspace, we cannot guarantee
that applications will only access the intended 4K shared region rather
than the full 64K page mapped into their address space. Such userspace
addresses may also be passed back into the kernel and accessed via the
linear map, resulting in a GPC fault and a kernel crash.

With CCA, although Stage-2 mappings managed by the RMM still operate at a
4K granularity, shared pages must nonetheless be aligned to the
host-managed page size and sized as whole host pages to avoid the issues
described above.

Introduce a new helper, mem_decrypt_align(), to allow callers to enforce
the required alignment and size constraints for shared buffers.

The architecture-specific implementation of mem_decrypt_align() will be
provided in a follow-up patch.

Note on restricted-dma-pool:
rmem_swiotlb_device_init() uses reserved-memory regions described by
firmware. Those regions are not changed in-kernel to satisfy host granule
alignment. This is intentional: we do not expect restricted-dma-pool
allocations to be used with CCA. If restricted-dma-pool is intended for CCA
shared use, firmware must provide base/size aligned to the host IPA-change
granule.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 arch/arm64/mm/mem_encrypt.c      | 19 +++++++++++++++----
 drivers/irqchip/irq-gic-v3-its.c | 20 +++++++++++++-------
 include/linux/mem_encrypt.h      | 14 ++++++++++++++
 kernel/dma/contiguous.c          | 10 ++++++++++
 kernel/dma/direct.c              | 16 ++++++++++++++--
 kernel/dma/pool.c                |  4 +++-
 kernel/dma/swiotlb.c             | 21 +++++++++++++--------
 7 files changed, 82 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/mm/mem_encrypt.c b/arch/arm64/mm/mem_encrypt.c
index ee3c0ab04384..38c62c9e4e74 100644
--- a/arch/arm64/mm/mem_encrypt.c
+++ b/arch/arm64/mm/mem_encrypt.c
@@ -17,8 +17,7 @@
 #include <linux/compiler.h>
 #include <linux/err.h>
 #include <linux/mm.h>
-
-#include <asm/mem_encrypt.h>
+#include <linux/mem_encrypt.h>
 
 static const struct arm64_mem_crypt_ops *crypt_ops;
 
@@ -33,18 +32,30 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops)
 
 int set_memory_encrypted(unsigned long addr, int numpages)
 {
-	if (likely(!crypt_ops) || WARN_ON(!PAGE_ALIGNED(addr)))
+	if (likely(!crypt_ops))
 		return 0;
 
+	if (WARN_ON(!IS_ALIGNED(addr, mem_decrypt_granule_size())))
+		return -EINVAL;
+
+	if (WARN_ON(!IS_ALIGNED(numpages << PAGE_SHIFT, mem_decrypt_granule_size())))
+		return -EINVAL;
+
 	return crypt_ops->encrypt(addr, numpages);
 }
 EXPORT_SYMBOL_GPL(set_memory_encrypted);
 
 int set_memory_decrypted(unsigned long addr, int numpages)
 {
-	if (likely(!crypt_ops) || WARN_ON(!PAGE_ALIGNED(addr)))
+	if (likely(!crypt_ops))
 		return 0;
 
+	if (WARN_ON(!IS_ALIGNED(addr, mem_decrypt_granule_size())))
+		return -EINVAL;
+
+	if (WARN_ON(!IS_ALIGNED(numpages << PAGE_SHIFT, mem_decrypt_granule_size())))
+		return -EINVAL;
+
 	return crypt_ops->decrypt(addr, numpages);
 }
 EXPORT_SYMBOL_GPL(set_memory_decrypted);
diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 291d7668cc8d..239d7e3bc16f 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -213,16 +213,17 @@ static gfp_t gfp_flags_quirk;
 static struct page *its_alloc_pages_node(int node, gfp_t gfp,
 					 unsigned int order)
 {
+	unsigned int new_order;
 	struct page *page;
 	int ret = 0;
 
-	page = alloc_pages_node(node, gfp | gfp_flags_quirk, order);
-
+	new_order = get_order(mem_decrypt_align((PAGE_SIZE << order)));
+	page = alloc_pages_node(node, gfp | gfp_flags_quirk, new_order);
 	if (!page)
 		return NULL;
 
 	ret = set_memory_decrypted((unsigned long)page_address(page),
-				   1 << order);
+				   1 << new_order);
 	/*
 	 * If set_memory_decrypted() fails then we don't know what state the
 	 * page is in, so we can't free it. Instead we leak it.
@@ -241,13 +242,16 @@ static struct page *its_alloc_pages(gfp_t gfp, unsigned int order)
 
 static void its_free_pages(void *addr, unsigned int order)
 {
+	int new_order;
+
+	new_order = get_order(mem_decrypt_align((PAGE_SIZE << order)));
 	/*
 	 * If the memory cannot be encrypted again then we must leak the pages.
 	 * set_memory_encrypted() will already have WARNed.
 	 */
-	if (set_memory_encrypted((unsigned long)addr, 1 << order))
+	if (set_memory_encrypted((unsigned long)addr, 1 << new_order))
 		return;
-	free_pages((unsigned long)addr, order);
+	free_pages((unsigned long)addr, new_order);
 }
 
 static struct gen_pool *itt_pool;
@@ -268,11 +272,13 @@ static void *itt_alloc_pool(int node, int size)
 		if (addr)
 			break;
 
-		page = its_alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
+		page = its_alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO,
+					    get_order(mem_decrypt_granule_size()));
 		if (!page)
 			break;
 
-		gen_pool_add(itt_pool, (unsigned long)page_address(page), PAGE_SIZE, node);
+		gen_pool_add(itt_pool, (unsigned long)page_address(page),
+			     mem_decrypt_granule_size(), node);
 	} while (!addr);
 
 	return (void *)addr;
diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
index 07584c5e36fb..1e01c9ac697f 100644
--- a/include/linux/mem_encrypt.h
+++ b/include/linux/mem_encrypt.h
@@ -11,6 +11,8 @@
 #define __MEM_ENCRYPT_H__
 
 #ifndef __ASSEMBLY__
+#include <linux/align.h>
+#include <vdso/page.h>
 
 #ifdef CONFIG_ARCH_HAS_MEM_ENCRYPT
 
@@ -54,6 +56,18 @@
 #define dma_addr_canonical(x)		(x)
 #endif
 
+#ifndef mem_decrypt_granule_size
+static inline size_t mem_decrypt_granule_size(void)
+{
+	return PAGE_SIZE;
+}
+#endif
+
+static inline size_t mem_decrypt_align(size_t size)
+{
+	return ALIGN(size, mem_decrypt_granule_size());
+}
+
 #endif	/* __ASSEMBLY__ */
 
 #endif	/* __MEM_ENCRYPT_H__ */
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index c56004d314dc..2b7ff68be0c4 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -46,6 +46,7 @@
 #include <linux/dma-map-ops.h>
 #include <linux/cma.h>
 #include <linux/nospec.h>
+#include <linux/dma-direct.h>
 
 #ifdef CONFIG_CMA_SIZE_MBYTES
 #define CMA_SIZE_MBYTES CONFIG_CMA_SIZE_MBYTES
@@ -374,6 +375,15 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
 #ifdef CONFIG_DMA_NUMA_CMA
 	int nid = dev_to_node(dev);
 #endif
+	/*
+	 * for untrusted device, we require the dma buffers to be aligned to
+	 * the mem_decrypt_align(PAGE_SIZE) so that we can set the memory
+	 * attributes correctly.
+	 */
+	if (force_dma_unencrypted(dev)) {
+		if (get_order(mem_decrypt_granule_size()) > CONFIG_CMA_ALIGNMENT)
+			return NULL;
+	}
 
 	/* CMA can be used only in the context which permits sleeping */
 	if (!gfpflags_allow_blocking(gfp))
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index c2a43e4ef902..34eccd047e9b 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -257,6 +257,9 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 		return NULL;
 	}
 
+	if (force_dma_unencrypted(dev))
+		size = mem_decrypt_align(size);
+
 	/* we always manually zero the memory once we are done */
 	page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
 	if (!page)
@@ -350,6 +353,9 @@ void dma_direct_free(struct device *dev, size_t size,
 	if (swiotlb_find_pool(dev, dma_to_phys(dev, dma_addr)))
 		mark_mem_encrypted = false;
 
+	if (mark_mem_encrypted && force_dma_unencrypted(dev))
+		size = mem_decrypt_align(size);
+
 	if (is_vmalloc_addr(cpu_addr)) {
 		vunmap(cpu_addr);
 	} else {
@@ -384,6 +390,9 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
 		goto setup_page;
 	}
 
+	if (force_dma_unencrypted(dev))
+		size = mem_decrypt_align(size);
+
 	page = __dma_direct_alloc_pages(dev, size, gfp, false);
 	if (!page)
 		return NULL;
@@ -414,8 +423,11 @@ void dma_direct_free_pages(struct device *dev, size_t size,
 	if (swiotlb_find_pool(dev, page_to_phys(page)))
 		mark_mem_encrypted = false;
 
-	if (mark_mem_encrypted && dma_set_encrypted(dev, vaddr, size))
-		return;
+	if (mark_mem_encrypted && force_dma_unencrypted(dev)) {
+		size = mem_decrypt_align(size);
+		if (dma_set_encrypted(dev, vaddr, size))
+			return;
+	}
 	__dma_direct_free_pages(dev, page, size);
 }
 
diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 2b2fbb709242..b5f10ba3e855 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -83,7 +83,9 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 	struct page *page = NULL;
 	void *addr;
 	int ret = -ENOMEM;
+	unsigned int min_encrypt_order = get_order(mem_decrypt_granule_size());
 
+	pool_size = mem_decrypt_align(pool_size);
 	/* Cannot allocate larger than MAX_PAGE_ORDER */
 	order = min(get_order(pool_size), MAX_PAGE_ORDER);
 
@@ -94,7 +96,7 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 							 order, false);
 		if (!page)
 			page = alloc_pages(gfp | __GFP_NOWARN, order);
-	} while (!page && order-- > 0);
+	} while (!page && order-- > min_encrypt_order);
 	if (!page)
 		goto out;
 
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 9fd73700ddcf..b5cf8cd65e77 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -261,7 +261,7 @@ void __init swiotlb_update_mem_attributes(void)
 
 	if (!mem->nslabs || mem->late_alloc)
 		return;
-	bytes = PAGE_ALIGN(mem->nslabs << IO_TLB_SHIFT);
+	bytes = mem_decrypt_align(mem->nslabs << IO_TLB_SHIFT);
 	set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
 }
 
@@ -318,8 +318,8 @@ static void __init *swiotlb_memblock_alloc(unsigned long nslabs,
 		unsigned int flags,
 		int (*remap)(void *tlb, unsigned long nslabs))
 {
-	size_t bytes = PAGE_ALIGN(nslabs << IO_TLB_SHIFT);
 	void *tlb;
+	size_t bytes = mem_decrypt_align(nslabs << IO_TLB_SHIFT);
 
 	/*
 	 * By default allocate the bounce buffer memory from low memory, but
@@ -327,9 +327,9 @@ static void __init *swiotlb_memblock_alloc(unsigned long nslabs,
 	 * memory encryption.
 	 */
 	if (flags & SWIOTLB_ANY)
-		tlb = memblock_alloc(bytes, PAGE_SIZE);
+		tlb = memblock_alloc(bytes, mem_decrypt_granule_size());
 	else
-		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
+		tlb = memblock_alloc_low(bytes, mem_decrypt_granule_size());
 
 	if (!tlb) {
 		pr_warn("%s: Failed to allocate %zu bytes tlb structure\n",
@@ -338,7 +338,7 @@ static void __init *swiotlb_memblock_alloc(unsigned long nslabs,
 	}
 
 	if (remap && remap(tlb, nslabs) < 0) {
-		memblock_free(tlb, PAGE_ALIGN(bytes));
+		memblock_free(tlb, bytes);
 		pr_warn("%s: Failed to remap %zu bytes\n", __func__, bytes);
 		return NULL;
 	}
@@ -460,7 +460,7 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
 		swiotlb_adjust_nareas(num_possible_cpus());
 
 retry:
-	order = get_order(nslabs << IO_TLB_SHIFT);
+	order = get_order(mem_decrypt_align(nslabs << IO_TLB_SHIFT));
 	nslabs = SLABS_PER_PAGE << order;
 
 	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
@@ -469,6 +469,8 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
 		if (vstart)
 			break;
 		order--;
+		if (order < get_order(mem_decrypt_granule_size()))
+			break;
 		nslabs = SLABS_PER_PAGE << order;
 		retried = true;
 	}
@@ -536,7 +538,7 @@ void __init swiotlb_exit(void)
 
 	pr_info("tearing down default memory pool\n");
 	tbl_vaddr = (unsigned long)phys_to_virt(mem->start);
-	tbl_size = PAGE_ALIGN(mem->end - mem->start);
+	tbl_size = mem_decrypt_align(mem->end - mem->start);
 	slots_size = PAGE_ALIGN(array_size(sizeof(*mem->slots), mem->nslabs));
 
 	set_memory_encrypted(tbl_vaddr, tbl_size >> PAGE_SHIFT);
@@ -572,11 +574,13 @@ void __init swiotlb_exit(void)
  */
 static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
 {
-	unsigned int order = get_order(bytes);
+	unsigned int order;
 	struct page *page;
 	phys_addr_t paddr;
 	void *vaddr;
 
+	bytes = mem_decrypt_align(bytes);
+	order = get_order(bytes);
 	page = alloc_pages(gfp, order);
 	if (!page)
 		return NULL;
@@ -659,6 +663,7 @@ static void swiotlb_free_tlb(void *vaddr, size_t bytes)
 	    dma_free_from_pool(NULL, vaddr, bytes))
 		return;
 
+	bytes = mem_decrypt_align(bytes);
 	/* Intentional leak if pages cannot be encrypted again. */
 	if (!set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
 		__free_pages(virt_to_page(vaddr), get_order(bytes));
-- 
2.43.0

[PATCH v4 3/3] coco: guest: arm64: Query host IPA-change alignment via RHI

[Aneesh Kumar K.V (Arm)]

Add the Realm Host Interface support needed to query host configuration
from a Realm guest. Define the RHI hostconf SMCs, add rsi_host_call(), and
use them during Realm initialization to retrieve the host IPA-change
alignment size.

Expose that alignment through realm_get_hyp_pagesize() and
mem_decrypt_granule_size() so shared-buffer allocation and
encryption/decryption paths can honor the ipa change page-size requirement.

If the host reports an invalid alignment (when alginment value is not
multiple of 4K), do not enable Realm support.

This provides the host alignment information required by the shared buffer
alignment changes.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 arch/arm64/include/asm/mem_encrypt.h |  3 ++
 arch/arm64/include/asm/rhi.h         | 24 +++++++++++++
 arch/arm64/include/asm/rsi.h         |  2 ++
 arch/arm64/include/asm/rsi_cmds.h    | 10 ++++++
 arch/arm64/include/asm/rsi_smc.h     |  7 ++++
 arch/arm64/kernel/Makefile           |  2 +-
 arch/arm64/kernel/rhi.c              | 54 ++++++++++++++++++++++++++++
 arch/arm64/kernel/rsi.c              | 13 +++++++
 arch/arm64/mm/mem_encrypt.c          |  8 +++++
 9 files changed, 122 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/include/asm/rhi.h
 create mode 100644 arch/arm64/kernel/rhi.c

diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h
index 314b2b52025f..5541911eb028 100644
--- a/arch/arm64/include/asm/mem_encrypt.h
+++ b/arch/arm64/include/asm/mem_encrypt.h
@@ -16,6 +16,9 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops);
 int set_memory_encrypted(unsigned long addr, int numpages);
 int set_memory_decrypted(unsigned long addr, int numpages);
 
+#define mem_decrypt_granule_size mem_decrypt_granule_size
+size_t mem_decrypt_granule_size(void);
+
 int realm_register_memory_enc_ops(void);
 
 static inline bool force_dma_unencrypted(struct device *dev)
diff --git a/arch/arm64/include/asm/rhi.h b/arch/arm64/include/asm/rhi.h
new file mode 100644
index 000000000000..0895dd92ea1d
--- /dev/null
+++ b/arch/arm64/include/asm/rhi.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ */
+
+#ifndef __ASM_RHI_H_
+#define __ASM_RHI_H_
+
+#include <linux/types.h>
+
+#define SMC_RHI_CALL(func)				\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,		\
+			   ARM_SMCCC_SMC_64,		\
+			   ARM_SMCCC_OWNER_STANDARD_HYP,\
+			   (func))
+
+unsigned long rhi_get_ipa_change_alignment(void);
+#define RHI_HOSTCONF_VER_1_0		0x10000
+#define RHI_HOSTCONF_VERSION		SMC_RHI_CALL(0x004E)
+
+#define __RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT BIT(0)
+#define RHI_HOSTCONF_FEATURES		SMC_RHI_CALL(0x004F)
+#define RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT	SMC_RHI_CALL(0x0050)
+#endif
diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
index 88b50d660e85..ae54fb3b1429 100644
--- a/arch/arm64/include/asm/rsi.h
+++ b/arch/arm64/include/asm/rsi.h
@@ -67,4 +67,6 @@ static inline int rsi_set_memory_range_shared(phys_addr_t start,
 	return rsi_set_memory_range(start, end, RSI_RIPAS_EMPTY,
 				    RSI_CHANGE_DESTROYED);
 }
+
+unsigned long realm_get_hyp_pagesize(void);
 #endif /* __ASM_RSI_H_ */
diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
index 2c8763876dfb..a341ce0eeda1 100644
--- a/arch/arm64/include/asm/rsi_cmds.h
+++ b/arch/arm64/include/asm/rsi_cmds.h
@@ -159,4 +159,14 @@ static inline unsigned long rsi_attestation_token_continue(phys_addr_t granule,
 	return res.a0;
 }
 
+static inline unsigned long rsi_host_call(struct rsi_host_call *rhi_call)
+{
+	phys_addr_t addr = virt_to_phys(rhi_call);
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(SMC_RSI_HOST_CALL, addr, &res);
+
+	return res.a0;
+}
+
 #endif /* __ASM_RSI_CMDS_H */
diff --git a/arch/arm64/include/asm/rsi_smc.h b/arch/arm64/include/asm/rsi_smc.h
index e19253f96c94..9ee8b5c7612e 100644
--- a/arch/arm64/include/asm/rsi_smc.h
+++ b/arch/arm64/include/asm/rsi_smc.h
@@ -182,6 +182,13 @@ struct realm_config {
  */
 #define SMC_RSI_IPA_STATE_GET			SMC_RSI_FID(0x198)
 
+struct rsi_host_call {
+	union {
+		u16 imm;
+		u64 padding0;
+	};
+	u64 gprs[31];
+} __aligned(0x100);
 /*
  * Make a Host call.
  *
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index fe627100d199..3e72dd9584ed 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -34,7 +34,7 @@ obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   cpufeature.o alternative.o cacheinfo.o		\
 			   smp.o smp_spin_table.o topology.o smccc-call.o	\
 			   syscall.o proton-pack.o idle.o patching.o pi/	\
-			   rsi.o jump_label.o
+			   rsi.o jump_label.o rhi.o
 
 obj-$(CONFIG_COMPAT)			+= sys32.o signal32.o			\
 					   sys_compat.o
diff --git a/arch/arm64/kernel/rhi.c b/arch/arm64/kernel/rhi.c
new file mode 100644
index 000000000000..7cd6c5102464
--- /dev/null
+++ b/arch/arm64/kernel/rhi.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ */
+
+#include <linux/mm.h>
+#include <asm/rsi.h>
+#include <asm/rhi.h>
+
+/* we need an aligned rhicall for rsi_host_call. slab is not yet ready */
+static struct rsi_host_call hyp_pagesize_rhicall;
+unsigned long rhi_get_ipa_change_alignment(void)
+{
+	long ret;
+	unsigned long ipa_change_align;
+
+	hyp_pagesize_rhicall.imm = 0;
+	hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_VERSION;
+	ret = rsi_host_call(lm_alias(&hyp_pagesize_rhicall));
+	if (ret != RSI_SUCCESS)
+		goto err_out;
+
+	if (hyp_pagesize_rhicall.gprs[0] != RHI_HOSTCONF_VER_1_0)
+		goto err_out;
+
+	hyp_pagesize_rhicall.imm = 0;
+	hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_FEATURES;
+	ret = rsi_host_call(lm_alias(&hyp_pagesize_rhicall));
+	if (ret != RSI_SUCCESS)
+		goto err_out;
+
+	if (!(hyp_pagesize_rhicall.gprs[0] & __RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT))
+		goto err_out;
+
+	hyp_pagesize_rhicall.imm = 0;
+	hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT;
+	ret = rsi_host_call(lm_alias(&hyp_pagesize_rhicall));
+	if (ret != RSI_SUCCESS)
+		goto err_out;
+
+	ipa_change_align = hyp_pagesize_rhicall.gprs[0];
+	/* This error needs special handling in the caller */
+	if (ipa_change_align & (SZ_4K - 1))
+		return 0;
+
+	return ipa_change_align;
+
+err_out:
+	/*
+	 * For failure condition assume host is built with 4K page size
+	 * and hence ipa change alignment can be guest PAGE_SIZE.
+	 */
+	return PAGE_SIZE;
+}
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 9e846ce4ef9c..ff735c04e236 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -14,8 +14,10 @@
 #include <asm/mem_encrypt.h>
 #include <asm/pgtable.h>
 #include <asm/rsi.h>
+#include <asm/rhi.h>
 
 static struct realm_config config;
+static unsigned long ipa_change_alignment = PAGE_SIZE;
 
 unsigned long prot_ns_shared;
 EXPORT_SYMBOL(prot_ns_shared);
@@ -139,6 +141,11 @@ static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
 	return 0;
 }
 
+unsigned long realm_get_hyp_pagesize(void)
+{
+	return ipa_change_alignment;
+}
+
 void __init arm64_rsi_init(void)
 {
 	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
@@ -147,6 +154,12 @@ void __init arm64_rsi_init(void)
 		return;
 	if (WARN_ON(rsi_get_realm_config(&config)))
 		return;
+
+	ipa_change_alignment = rhi_get_ipa_change_alignment();
+	/* If we don't get a correct alignment response, don't enable realm */
+	if (!ipa_change_alignment)
+		return;
+
 	prot_ns_shared = __phys_to_pte_val(BIT(config.ipa_bits - 1));
 
 	if (arm64_ioremap_prot_hook_register(realm_ioremap_hook))
diff --git a/arch/arm64/mm/mem_encrypt.c b/arch/arm64/mm/mem_encrypt.c
index 38c62c9e4e74..f5d64bc29c20 100644
--- a/arch/arm64/mm/mem_encrypt.c
+++ b/arch/arm64/mm/mem_encrypt.c
@@ -59,3 +59,11 @@ int set_memory_decrypted(unsigned long addr, int numpages)
 	return crypt_ops->decrypt(addr, numpages);
 }
 EXPORT_SYMBOL_GPL(set_memory_decrypted);
+
+size_t mem_decrypt_granule_size(void)
+{
+	if (is_realm_world())
+		return max(PAGE_SIZE, realm_get_hyp_pagesize());
+	return PAGE_SIZE;
+}
+EXPORT_SYMBOL_GPL(mem_decrypt_granule_size);
-- 
2.43.0

Re: [PATCH v4 2/3] swiotlb: dma: its: Enforce host page-size alignment for shared buffers

[Marc Zyngier]

On Mon, 27 Apr 2026 07:31:07 +0100,
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org> wrote:
> 
> When running private-memory guests, the guest kernel must apply additional
> constraints when allocating buffers that are shared with the hypervisor.
> 
> These shared buffers are also accessed by the host kernel and therefore
> must be aligned to the host’s page size, and have a size that is a multiple
> of the host page size.
> 
> On non-secure hosts, set_guest_memory_attributes() tracks memory at the
> host PAGE_SIZE granularity. This creates a mismatch when the guest applies
> attributes at 4K boundaries while the host uses 64K pages. In such cases,
> set_guest_memory_attributes() call returns -EINVAL, preventing the
> conversion of memory regions from private to shared.
> 
> Architectures such as Arm can tolerate realm physical address space
> (protected memory) PFNs being mapped as shared memory, as incorrect
> accesses are detected and reported as GPC faults. However, relying on this
> mechanism is unsafe and can still lead to kernel crashes.
> 
> This is particularly likely when guest_memfd allocations are mmapped and
> accessed from userspace. Once exposed to userspace, we cannot guarantee
> that applications will only access the intended 4K shared region rather
> than the full 64K page mapped into their address space. Such userspace
> addresses may also be passed back into the kernel and accessed via the
> linear map, resulting in a GPC fault and a kernel crash.
> 
> With CCA, although Stage-2 mappings managed by the RMM still operate at a
> 4K granularity, shared pages must nonetheless be aligned to the
> host-managed page size and sized as whole host pages to avoid the issues
> described above.

I thought that was being fixed, and that there was now a strong
guarantee that RMM and host are aligned on the page size. Even more,
S2 is totally irrelevant here. The only thing that matters is the host
page size vs the guest page size. Nothing else.

> 
> Introduce a new helper, mem_decrypt_align(), to allow callers to enforce
> the required alignment and size constraints for shared buffers.
> 
> The architecture-specific implementation of mem_decrypt_align() will be
> provided in a follow-up patch.
> 
> Note on restricted-dma-pool:
> rmem_swiotlb_device_init() uses reserved-memory regions described by
> firmware. Those regions are not changed in-kernel to satisfy host granule
> alignment. This is intentional: we do not expect restricted-dma-pool
> allocations to be used with CCA. If restricted-dma-pool is intended for CCA
> shared use, firmware must provide base/size aligned to the host IPA-change
> granule.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  arch/arm64/mm/mem_encrypt.c      | 19 +++++++++++++++----
>  drivers/irqchip/irq-gic-v3-its.c | 20 +++++++++++++-------
>  include/linux/mem_encrypt.h      | 14 ++++++++++++++
>  kernel/dma/contiguous.c          | 10 ++++++++++
>  kernel/dma/direct.c              | 16 ++++++++++++++--
>  kernel/dma/pool.c                |  4 +++-
>  kernel/dma/swiotlb.c             | 21 +++++++++++++--------
>  7 files changed, 82 insertions(+), 22 deletions(-)
> 

[...]

> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 291d7668cc8d..239d7e3bc16f 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -213,16 +213,17 @@ static gfp_t gfp_flags_quirk;
>  static struct page *its_alloc_pages_node(int node, gfp_t gfp,
>  					 unsigned int order)
>  {
> +	unsigned int new_order;
>  	struct page *page;
>  	int ret = 0;
>  
> -	page = alloc_pages_node(node, gfp | gfp_flags_quirk, order);
> -
> +	new_order = get_order(mem_decrypt_align((PAGE_SIZE << order)));
> +	page = alloc_pages_node(node, gfp | gfp_flags_quirk, new_order);
>  	if (!page)
>  		return NULL;
>  
>  	ret = set_memory_decrypted((unsigned long)page_address(page),
> -				   1 << order);
> +				   1 << new_order);
>  	/*
>  	 * If set_memory_decrypted() fails then we don't know what state the
>  	 * page is in, so we can't free it. Instead we leak it.
> @@ -241,13 +242,16 @@ static struct page *its_alloc_pages(gfp_t gfp, unsigned int order)
>  
>  static void its_free_pages(void *addr, unsigned int order)
>  {
> +	int new_order;
> +
> +	new_order = get_order(mem_decrypt_align((PAGE_SIZE << order)));
>  	/*
>  	 * If the memory cannot be encrypted again then we must leak the pages.
>  	 * set_memory_encrypted() will already have WARNed.
>  	 */
> -	if (set_memory_encrypted((unsigned long)addr, 1 << order))
> +	if (set_memory_encrypted((unsigned long)addr, 1 << new_order))
>  		return;
> -	free_pages((unsigned long)addr, order);
> +	free_pages((unsigned long)addr, new_order);
>  }
>

Here's the non-obfuscated version of the two hunks above (and let it
be on the record that New Order is a terrible, overrated band):

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 291d7668cc8da..a4d555aaee241 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -216,6 +216,7 @@ static struct page *its_alloc_pages_node(int node, gfp_t gfp,
 	struct page *page;
 	int ret = 0;
 
+	order = get_order(mem_decrypt_align(PAGE_SIZE << order));
 	page = alloc_pages_node(node, gfp | gfp_flags_quirk, order);
 
 	if (!page)
@@ -245,6 +246,7 @@ static void its_free_pages(void *addr, unsigned int order)
 	 * If the memory cannot be encrypted again then we must leak the pages.
 	 * set_memory_encrypted() will already have WARNed.
 	 */
+	order = get_order(mem_decrypt_align(PAGE_SIZE << order));
 	if (set_memory_encrypted((unsigned long)addr, 1 << order))
 		return;
 	free_pages((unsigned long)addr, order);

>  static struct gen_pool *itt_pool;
> @@ -268,11 +272,13 @@ static void *itt_alloc_pool(int node, int size)
>  		if (addr)
>  			break;
>  
> -		page = its_alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
> +		page = its_alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO,
> +					    get_order(mem_decrypt_granule_size()));

You already taught its_alloc_pages_node() about the decrypt granule
size stuff. I don't think we need to see more of it (and you don't
mess with the call that is just above it).

>  		if (!page)
>  			break;
>  
> -		gen_pool_add(itt_pool, (unsigned long)page_address(page), PAGE_SIZE, node);
> +		gen_pool_add(itt_pool, (unsigned long)page_address(page),
> +			     mem_decrypt_granule_size(), node);

I'd rather see something like mem_decrypt_align(PAGE_SIZE), which
keeps the intent clear.

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v4 3/3] coco: guest: arm64: Query host IPA-change alignment via RHI

[Marc Zyngier]

On Mon, 27 Apr 2026 07:31:08 +0100,
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org> wrote:
> 
> Add the Realm Host Interface support needed to query host configuration
> from a Realm guest. Define the RHI hostconf SMCs, add rsi_host_call(), and
> use them during Realm initialization to retrieve the host IPA-change
> alignment size.

I don't understand what "IPA-change" means. What you are after is the
host's sharing granule size.

> 
> Expose that alignment through realm_get_hyp_pagesize() and
> mem_decrypt_granule_size() so shared-buffer allocation and
> encryption/decryption paths can honor the ipa change page-size requirement.
> 
> If the host reports an invalid alignment (when alginment value is not
> multiple of 4K), do not enable Realm support.
> 
> This provides the host alignment information required by the shared buffer
> alignment changes.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  arch/arm64/include/asm/mem_encrypt.h |  3 ++
>  arch/arm64/include/asm/rhi.h         | 24 +++++++++++++
>  arch/arm64/include/asm/rsi.h         |  2 ++
>  arch/arm64/include/asm/rsi_cmds.h    | 10 ++++++
>  arch/arm64/include/asm/rsi_smc.h     |  7 ++++
>  arch/arm64/kernel/Makefile           |  2 +-
>  arch/arm64/kernel/rhi.c              | 54 ++++++++++++++++++++++++++++
>  arch/arm64/kernel/rsi.c              | 13 +++++++
>  arch/arm64/mm/mem_encrypt.c          |  8 +++++
>  9 files changed, 122 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/rhi.h
>  create mode 100644 arch/arm64/kernel/rhi.c
> 
> diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h
> index 314b2b52025f..5541911eb028 100644
> --- a/arch/arm64/include/asm/mem_encrypt.h
> +++ b/arch/arm64/include/asm/mem_encrypt.h
> @@ -16,6 +16,9 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops);
>  int set_memory_encrypted(unsigned long addr, int numpages);
>  int set_memory_decrypted(unsigned long addr, int numpages);
>  
> +#define mem_decrypt_granule_size mem_decrypt_granule_size
> +size_t mem_decrypt_granule_size(void);
> +
>  int realm_register_memory_enc_ops(void);
>  
>  static inline bool force_dma_unencrypted(struct device *dev)
> diff --git a/arch/arm64/include/asm/rhi.h b/arch/arm64/include/asm/rhi.h
> new file mode 100644
> index 000000000000..0895dd92ea1d
> --- /dev/null
> +++ b/arch/arm64/include/asm/rhi.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2026 ARM Ltd.
> + */
> +
> +#ifndef __ASM_RHI_H_
> +#define __ASM_RHI_H_
> +
> +#include <linux/types.h>
> +
> +#define SMC_RHI_CALL(func)				\
> +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,		\
> +			   ARM_SMCCC_SMC_64,		\
> +			   ARM_SMCCC_OWNER_STANDARD_HYP,\
> +			   (func))
> +
> +unsigned long rhi_get_ipa_change_alignment(void);
> +#define RHI_HOSTCONF_VER_1_0		0x10000
> +#define RHI_HOSTCONF_VERSION		SMC_RHI_CALL(0x004E)
> +
> +#define __RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT BIT(0)
> +#define RHI_HOSTCONF_FEATURES		SMC_RHI_CALL(0x004F)
> +#define RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT	SMC_RHI_CALL(0x0050)
> +#endif
> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> index 88b50d660e85..ae54fb3b1429 100644
> --- a/arch/arm64/include/asm/rsi.h
> +++ b/arch/arm64/include/asm/rsi.h
> @@ -67,4 +67,6 @@ static inline int rsi_set_memory_range_shared(phys_addr_t start,
>  	return rsi_set_memory_range(start, end, RSI_RIPAS_EMPTY,
>  				    RSI_CHANGE_DESTROYED);
>  }
> +
> +unsigned long realm_get_hyp_pagesize(void);
>  #endif /* __ASM_RSI_H_ */
> diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
> index 2c8763876dfb..a341ce0eeda1 100644
> --- a/arch/arm64/include/asm/rsi_cmds.h
> +++ b/arch/arm64/include/asm/rsi_cmds.h
> @@ -159,4 +159,14 @@ static inline unsigned long rsi_attestation_token_continue(phys_addr_t granule,
>  	return res.a0;
>  }
>  
> +static inline unsigned long rsi_host_call(struct rsi_host_call *rhi_call)
> +{
> +	phys_addr_t addr = virt_to_phys(rhi_call);
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_1_1_invoke(SMC_RSI_HOST_CALL, addr, &res);

Errr... What guarantees that *rhi_call is *IPA contiguous*? This is
incredibly fragile. You should at the very least check that this isn't
vmalloc'd.

> +
> +	return res.a0;
> +}
> +
>  #endif /* __ASM_RSI_CMDS_H */
> diff --git a/arch/arm64/include/asm/rsi_smc.h b/arch/arm64/include/asm/rsi_smc.h
> index e19253f96c94..9ee8b5c7612e 100644
> --- a/arch/arm64/include/asm/rsi_smc.h
> +++ b/arch/arm64/include/asm/rsi_smc.h
> @@ -182,6 +182,13 @@ struct realm_config {
>   */
>  #define SMC_RSI_IPA_STATE_GET			SMC_RSI_FID(0x198)
>  
> +struct rsi_host_call {
> +	union {
> +		u16 imm;
> +		u64 padding0;
> +	};
> +	u64 gprs[31];
> +} __aligned(0x100);
>  /*
>   * Make a Host call.
>   *
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index fe627100d199..3e72dd9584ed 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -34,7 +34,7 @@ obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
>  			   cpufeature.o alternative.o cacheinfo.o		\
>  			   smp.o smp_spin_table.o topology.o smccc-call.o	\
>  			   syscall.o proton-pack.o idle.o patching.o pi/	\
> -			   rsi.o jump_label.o
> +			   rsi.o jump_label.o rhi.o
>  
>  obj-$(CONFIG_COMPAT)			+= sys32.o signal32.o			\
>  					   sys_compat.o
> diff --git a/arch/arm64/kernel/rhi.c b/arch/arm64/kernel/rhi.c
> new file mode 100644
> index 000000000000..7cd6c5102464
> --- /dev/null
> +++ b/arch/arm64/kernel/rhi.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2026 ARM Ltd.
> + */
> +
> +#include <linux/mm.h>
> +#include <asm/rsi.h>
> +#include <asm/rhi.h>
> +
> +/* we need an aligned rhicall for rsi_host_call. slab is not yet ready */
> +static struct rsi_host_call hyp_pagesize_rhicall;

Why the "hyp_" prefix? This has absolutely nothing to with the
hypervisor.

> +unsigned long rhi_get_ipa_change_alignment(void)
> +{
> +	long ret;
> +	unsigned long ipa_change_align;
> +
> +	hyp_pagesize_rhicall.imm = 0;
> +	hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_VERSION;
> +	ret = rsi_host_call(lm_alias(&hyp_pagesize_rhicall));
> +	if (ret != RSI_SUCCESS)
> +		goto err_out;
> +
> +	if (hyp_pagesize_rhicall.gprs[0] != RHI_HOSTCONF_VER_1_0)
> +		goto err_out;
> +
> +	hyp_pagesize_rhicall.imm = 0;
> +	hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_FEATURES;
> +	ret = rsi_host_call(lm_alias(&hyp_pagesize_rhicall));
> +	if (ret != RSI_SUCCESS)
> +		goto err_out;
> +
> +	if (!(hyp_pagesize_rhicall.gprs[0] & __RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT))
> +		goto err_out;
> +
> +	hyp_pagesize_rhicall.imm = 0;
> +	hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT;
> +	ret = rsi_host_call(lm_alias(&hyp_pagesize_rhicall));
> +	if (ret != RSI_SUCCESS)
> +		goto err_out;
> +
> +	ipa_change_align = hyp_pagesize_rhicall.gprs[0];
> +	/* This error needs special handling in the caller */
> +	if (ipa_change_align & (SZ_4K - 1))
> +		return 0;
> +
> +	return ipa_change_align;
> +
> +err_out:
> +	/*
> +	 * For failure condition assume host is built with 4K page size
> +	 * and hence ipa change alignment can be guest PAGE_SIZE.
> +	 */
> +	return PAGE_SIZE;
> +}

Why can't this be part of rsi.c? This is an RSI call, and it should be
part of the RSI initialisation.

> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> index 9e846ce4ef9c..ff735c04e236 100644
> --- a/arch/arm64/kernel/rsi.c
> +++ b/arch/arm64/kernel/rsi.c
> @@ -14,8 +14,10 @@
>  #include <asm/mem_encrypt.h>
>  #include <asm/pgtable.h>
>  #include <asm/rsi.h>
> +#include <asm/rhi.h>
>  
>  static struct realm_config config;
> +static unsigned long ipa_change_alignment = PAGE_SIZE;
>  
>  unsigned long prot_ns_shared;
>  EXPORT_SYMBOL(prot_ns_shared);
> @@ -139,6 +141,11 @@ static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
>  	return 0;
>  }
>  
> +unsigned long realm_get_hyp_pagesize(void)
> +{
> +	return ipa_change_alignment;
> +}

Again, this has nothing to do with the hypervisor, but the host. And
ipa_change_alignment is still a wording I can't wrap my small head
around.

> +
>  void __init arm64_rsi_init(void)
>  {
>  	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
> @@ -147,6 +154,12 @@ void __init arm64_rsi_init(void)
>  		return;
>  	if (WARN_ON(rsi_get_realm_config(&config)))
>  		return;
> +
> +	ipa_change_alignment = rhi_get_ipa_change_alignment();
> +	/* If we don't get a correct alignment response, don't enable realm */
> +	if (!ipa_change_alignment)
> +		return;

But at the same time, you override a global value with an error, and
then paper over it in mem_decrypt_granule_size()...

> +
>  	prot_ns_shared = __phys_to_pte_val(BIT(config.ipa_bits - 1));
>  
>  	if (arm64_ioremap_prot_hook_register(realm_ioremap_hook))
> diff --git a/arch/arm64/mm/mem_encrypt.c b/arch/arm64/mm/mem_encrypt.c
> index 38c62c9e4e74..f5d64bc29c20 100644
> --- a/arch/arm64/mm/mem_encrypt.c
> +++ b/arch/arm64/mm/mem_encrypt.c
> @@ -59,3 +59,11 @@ int set_memory_decrypted(unsigned long addr, int numpages)
>  	return crypt_ops->decrypt(addr, numpages);
>  }
>  EXPORT_SYMBOL_GPL(set_memory_decrypted);
> +
> +size_t mem_decrypt_granule_size(void)
> +{
> +	if (is_realm_world())
> +		return max(PAGE_SIZE, realm_get_hyp_pagesize());

If you didn't mess with ipa_change_alignment above, you shouldn't need
this max().

	M.

-- 
Without deviation from the norm, progress is not possible.