um: remove copy_from_kernel_nofault_allowed

There is no need to override the default version of this function
anymore as UML now has proper _nofault memory access functions.

Doing this also fixes the fact that the implementation was incorrect as
using mincore() will incorrectly flag pages as inaccessible if they were
swapped out by the host.

Fixes: f75b1b1 ("um: Implement probe_kernel_read()")
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250210160926.420133-3-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: benzea

arch/um/include/shared/os.h

@@ -213,7 +213,6 @@ extern int os_protect_memory(void *addr, unsigned long len,
 extern int os_unmap_memory(void *addr, int len);
 extern int os_drop_memory(void *addr, int length);
 extern int can_drop_memory(void);
-extern int os_mincore(void *addr, unsigned long len);
 
 void os_set_pdeathsig(void);
 

arch/um/kernel/Makefile

@@ -17,7 +17,7 @@ extra-y := vmlinux.lds
 obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
 	physmem.o process.o ptrace.o reboot.o sigio.o \
 	signal.o sysrq.o time.o tlb.o trap.o \
-	um_arch.o umid.o maccess.o kmsg_dump.o capflags.o skas/
+	um_arch.o umid.o kmsg_dump.o capflags.o skas/
 obj-y += load_file.o
 
 obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o

arch/um/kernel/maccess.c

@@ -142,57 +142,6 @@ int __init can_drop_memory(void)
 	return ok;
 }
 
-static int os_page_mincore(void *addr)
-{
-	char vec[2];
-	int ret;
-
-	ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
-	if (ret < 0) {
-		if (errno == ENOMEM || errno == EINVAL)
-			return 0;
-		else
-			return -errno;
-	}
-
-	return vec[0] & 1;
-}
-
-int os_mincore(void *addr, unsigned long len)
-{
-	char *vec;
-	int ret, i;
-
-	if (len <= UM_KERN_PAGE_SIZE)
-		return os_page_mincore(addr);
-
-	vec = calloc(1, (len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE);
-	if (!vec)
-		return -ENOMEM;
-
-	ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
-	if (ret < 0) {
-		if (errno == ENOMEM || errno == EINVAL)
-			ret = 0;
-		else
-			ret = -errno;
-
-		goto out;
-	}
-
-	for (i = 0; i < ((len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE); i++) {
-		if (!(vec[i] & 1)) {
-			ret = 0;
-			goto out;
-		}
-	}
-
-	ret = 1;
-out:
-	free(vec);
-	return ret;
-}
-
 void init_new_thread_signals(void)
 {
 	set_handler(SIGSEGV);