um: Count iomem_size only once in physmem calculation

When calculating max_physmem, we've already factored in the space
used by iomem. We don't need to subtract it again.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241128081939.2216246-4-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: btw616

arch/um/kernel/um_arch.c

@@ -376,9 +376,8 @@ int __init linux_main(int argc, char **argv, char **envp)
 	iomem_size = (iomem_size + PAGE_SIZE - 1) & PAGE_MASK;
 
 	max_physmem = TASK_SIZE - uml_physmem - iomem_size - MIN_VMALLOC;
-
-	if (physmem_size + iomem_size > max_physmem) {
-		physmem_size = max_physmem - iomem_size;
+	if (physmem_size > max_physmem) {
+		physmem_size = max_physmem;
 		os_info("Physical memory size shrunk to %llu bytes\n",
 			physmem_size);
 	}