On Wed, Jun 05, 2024 at 10:30:01AM +0100, Steven Price wrote:

+static int __set_memory_encrypted(unsigned long addr,
+				  int numpages,
+				  bool encrypt)
+{
+	unsigned long set_prot = 0, clear_prot = 0;
+	phys_addr_t start, 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;
+
+	/*
+	 * Break the mapping before we make any changes to avoid stale TLB
+	 * entries or Synchronous External Aborts caused by RIPAS_EMPTY
+	 */
+	ret = __change_memory_common(addr, PAGE_SIZE * numpages,
+				     __pgprot(0),
+				     __pgprot(PTE_VALID));
+
+	if (encrypt) {
+		clear_prot = PROT_NS_SHARED;
+		ret = rsi_set_memory_range_protected(start, end);
+	} else {
+		set_prot = PROT_NS_SHARED;
+		ret = rsi_set_memory_range_shared(start, end);
+	}
+
+	if (ret)
+		return ret;
+
+	set_prot |= PTE_VALID;
+
+	return __change_memory_common(addr, PAGE_SIZE * numpages,
+				      __pgprot(set_prot),
+				      __pgprot(clear_prot));
+}

This works, does break-before-make and also rejects vmalloc() ranges
(for the time being).

One particular aspect I don't like is doing the TLBI twice. It's
sufficient to do it when you first make the pte invalid. We could guess
this in __change_memory_common() if set_mask has PTE_VALID. The call
sites are restricted to this file, just add a comment. An alternative
would be to add a bool flush argument to this function.

-- 
Catalin

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