[PATCH 2/2] arm64: Add encrypt/decrypt support for vmalloc regions

[Shanker Donthineni <sdonthineni@nvidia.com>]

On ARM64 systems with CCA (Confidential Compute Architecture) enabled,
the kernel may need to change the encryption attributes of memory
regions. The existing implementation of set_memory_encrypted() and
set_memory_decrypted() assumes that the input address is part of the
linear mapping region '__is_lm_address()', and fails with -EINVAL
otherwise.

This breaks use cases where the memory region resides in the vmalloc
area, which is mapped in non-linear mapping region.

This patch introduces a new helper, realm_set_memory(), which detects
whether the given address is from a non-linear mapping. If so, it uses
vmalloc_to_page() to resolve each page’s physical address and applies
attribute changes one page at a time. For the linear address regions,
it maintains the existing fast-path.

This change ensures that encrypted/decrypted memory attribute updates
correctly for all memory regions, including those allocated via vmap(),
module allocations, or other vmalloc-backed paths.

Call stack of Realm crash, QEMU hypervisor + NVME device (emulated):
 ...
 Freeing unused kernel memory: 6336K
 Run /sbin/init as init process
 Internal error: synchronous external abort: 0000000096000250 [#1]  SMP
 Modules linked in:
 CPU: 0 UID: 0 PID: 64 Comm: lsblk Not tainted 6.15.5 #2 PREEMPT(undef)
 Hardware name: linux,dummy-virt (DT)
 pstate: 43400005 (nZcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
 pc : __pi_memset_generic+0x16c/0x188
 lr : dma_alloc_from_pool+0xd0/0x1b8
 sp : ffff80008335b350
 x29: ffff80008335b350 x28: ffff800083162000 x27: ffff80008335b3c0
 x26: ffff80008144f000 x25: ffff8000801a27e8 x24: ffff800081e14000
 x23: ffffc1ffc0000000 x22: 0000000000001000 x21: ffff800081458310
 x20: 0000000042a40000 x19: ffff00000232fcc0 x18: 0000000000200000
 x17: 00000000000120c0 x16: ffff0000795520c0 x15: 0000000000000000
 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
 x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
 x8 : ffff800083162000 x7 : 0000000000000000 x6 : 000000000000003f
 x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000004
 x2 : 0000000000000fc0 x1 : 0000000000000000 x0 : ffff800083162000
 Call trace:
   __pi_memset_generic+0x16c/0x188 (P)
   dma_direct_alloc_from_pool+0xc4/0x230
   dma_direct_alloc+0x80/0x4a0
   dma_alloc_attrs+0x94/0x238
   dma_pool_alloc+0x128/0x258
   nvme_prep_rq.part.0+0x5f0/0x950
   nvme_queue_rq+0x78/0x1e8
   blk_mq_dispatch_rq_list+0x10c/0x6f0
   __blk_mq_sched_dispatch_requests+0x4a0/0x580
   blk_mq_sched_dispatch_requests+0x38/0xa0
   blk_mq_run_hw_queue+0x288/0x2f8
   blk_mq_flush_plug_list+0x134/0x630
   __blk_flush_plug+0x100/0x168
   blk_finish_plug+0x40/0x60
   read_pages+0x1a0/0x2b0
   page_cache_ra_unbounded+0x1f8/0x268
   force_page_cache_ra+0xa4/0xe0
   page_cache_sync_ra+0x48/0x268
   filemap_get_pages+0xf4/0x7a0
   filemap_read+0xf0/0x448
   blkdev_read_iter+0x8c/0x1a8
   vfs_read+0x288/0x330
   ksys_read+0x78/0x118
   __arm64_sys_read+0x24/0x40
   invoke_syscall+0x50/0x120
   el0_svc_common.constprop.0+0x48/0xf0
   do_el0_svc+0x24/0x38
   el0_svc+0x34/0xf8
   el0t_64_sync_handler+0x10c/0x138
   el0t_64_sync+0x1ac/0x1b0

Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
---
 arch/arm64/mm/pageattr.c | 55 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 48 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 04d4a8f676db4..65c3322a86b49 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -202,21 +202,26 @@ int set_direct_map_default_noflush(struct page *page)
 				   PAGE_SIZE, change_page_range, &data);
 }
 
+/*
+ * Common function for setting memory encryption or decryption attributes.
+ *
+ * @addr:        Virtual start address of the memory region
+ * @start:       Corresponding physical start address
+ * @numpages:    Number of pages to update
+ * @encrypt:     If true, set memory as encrypted; if false, decrypt
+ */
 static int __set_memory_enc_dec(unsigned long addr,
+				phys_addr_t start,
 				int numpages,
 				bool encrypt)
 {
 	unsigned long set_prot = 0, clear_prot = 0;
-	phys_addr_t start, end;
+	phys_addr_t end;
 	int ret;
 
 	if (!is_realm_world())
 		return 0;
 
-	if (!__is_lm_address(addr))
-		return -EINVAL;
-
-	start = __virt_to_phys(addr);
 	end = start + numpages * PAGE_SIZE;
 
 	if (encrypt)
@@ -248,9 +253,45 @@ static int __set_memory_enc_dec(unsigned long addr,
 				      __pgprot(0));
 }
 
+/*
+ * Wrapper for __set_memory_enc_dec() that handles both linear-mapped
+ * and vmalloc/module memory regions.
+ *
+ * If the address is in the linear map, we can directly compute the
+ * physical address. If not (e.g. vmalloc memory), we walk each page
+ * and call the attribute update individually.
+ */
+static int realm_set_memory(unsigned long addr, int numpages, bool encrypt)
+{
+	phys_addr_t start;
+	struct page *page;
+	int ret, i;
+
+	if (__is_lm_address(addr)) {
+		start = __virt_to_phys(addr);
+		return __set_memory_enc_dec(addr, start, numpages, encrypt);
+	}
+
+	for (i = 0; i < numpages; i++) {
+		page = vmalloc_to_page((void *)addr);
+		if (!page)
+			return -EINVAL;
+
+		start = page_to_phys(page);
+		ret = __set_memory_enc_dec(addr, start, 1, encrypt);
+		if (ret)
+			return ret;
+
+		addr += PAGE_SIZE;
+	}
+
+	return 0;
+}
+
 static int realm_set_memory_encrypted(unsigned long addr, int numpages)
 {
-	int ret = __set_memory_enc_dec(addr, numpages, true);
+	int ret = realm_set_memory(addr, numpages, true);
+
 
 	/*
 	 * If the request to change state fails, then the only sensible cause
@@ -264,7 +305,7 @@ static int realm_set_memory_encrypted(unsigned long addr, int numpages)
 
 static int realm_set_memory_decrypted(unsigned long addr, int numpages)
 {
-	int ret = __set_memory_enc_dec(addr, numpages, false);
+	int ret = realm_set_memory(addr, numpages, false);
 
 	WARN(ret, "Failed to decrypt memory, %d pages will be leaked",
 	     numpages);
-- 
2.25.1