s390/pageattr: Implement missing kernel_page_present()

kernel_page_present() was intentionally not implemented when adding
ARCH_HAS_SET_DIRECT_MAP support, since it was only used for suspend/resume
which is not supported anymore on s390.

A new bpf use case led to a compile error specific to s390. Even though
this specific use case went away implement kernel_page_present(), so that
the API is complete and potential future users won't run into this problem.

Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Closes: https://lore.kernel.org/all/045de961-ac69-40cc-b141-ab70ec9377ec@iogearbox.net
Fixes: 0490d6d ("s390/mm: enable ARCH_HAS_SET_DIRECT_MAP")
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: hcahca

arch/s390/include/asm/set_memory.h

@@ -62,5 +62,6 @@ __SET_MEMORY_FUNC(set_memory_4k, SET_MEMORY_4K)
 
 int set_direct_map_invalid_noflush(struct page *page);
 int set_direct_map_default_noflush(struct page *page);
+bool kernel_page_present(struct page *page);
 
 #endif

arch/s390/mm/pageattr.c

@@ -406,6 +406,21 @@ int set_direct_map_default_noflush(struct page *page)
 	return __set_memory((unsigned long)page_to_virt(page), 1, SET_MEMORY_DEF);
 }
 
+bool kernel_page_present(struct page *page)
+{
+	unsigned long addr;
+	unsigned int cc;
+
+	addr = (unsigned long)page_address(page);
+	asm volatile(
+		"	lra	%[addr],0(%[addr])\n"
+		"	ipm	%[cc]\n"
+		: [cc] "=d" (cc), [addr] "+a" (addr)
+		:
+		: "cc");
+	return (cc >> 28) == 0;
+}
+
 #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KFENCE)
 
 static void ipte_range(pte_t *pte, unsigned long address, int nr)