[PATCH v6 1/9] mm/mem_encrypt: Add helpers for shared-buffer alignment

confidential-computing guests may require shared buffers with alignment
larger than the guest page size. As these buffers are shared with the host,
which may manage shared/private state at a different page-size granularity,
the required alignment must account for the host's page size as well.

Add helpers for querying the shared-buffer granule size and for rounding
sizes up to that granule. The generic implementation defaults to PAGE_SIZE
so that existing architectures keep their current behaviour unless they
override the granule size.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 include/linux/mem_encrypt.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
index 07584c5e36fb..5d2a868f8d3d 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_cc_shared_granule_size
+static inline size_t mem_cc_shared_granule_size(void)
+{
+	return PAGE_SIZE;
+}
+#endif
+
+static inline size_t mem_cc_align_to_shared_granule(size_t size)
+{
+	return ALIGN(size, mem_cc_shared_granule_size());
+}
+
 #endif	/* __ASSEMBLY__ */
 
 #endif	/* __MEM_ENCRYPT_H__ */

-- 
2.43.0