Re: [PATCH 1/2] kdump: vmcore: move copy_to() from vmcore.c to uaccess.h

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On 12/11/2021 12:59 AM, Andrew Morton wrote:
On Fri, 10 Dec 2021 21:36:00 +0800 Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:

In arch/*/kernel/crash_dump*.c, there exist similar code about
copy_oldmem_page(), move copy_to() from vmcore.c to uaccess.h,
and then we can use copy_to() to simplify the related code.

...

--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -238,20 +238,6 @@ copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
 	return copy_oldmem_page(pfn, buf, csize, offset, userbuf);
 }

-/*
- * Copy to either kernel or user space
- */
-static int copy_to(void *target, void *src, size_t size, int userbuf)
-{
-	if (userbuf) {
-		if (copy_to_user((char __user *) target, src, size))
-			return -EFAULT;
-	} else {
-		memcpy(target, src, size);
-	}
-	return 0;
-}
-
 #ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
 static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
 {
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index ac03940..4a6c3e4 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -201,6 +201,20 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
 	return n;
 }

+/*
+ * Copy to either kernel or user space
+ */
+static inline int copy_to(void *target, void *src, size_t size, int userbuf)
+{
+	if (userbuf) {
+		if (copy_to_user((char __user *) target, src, size))
+			return -EFAULT;
+	} else {
+		memcpy(target, src, size);
+	}
+	return 0;
+}
+

Ordinarily I'd say "this is too large to be inlined".  But the function
has only a single callsite per architecture so inlining it won't cause
bloat at present.

But hopefully copy_to() will get additional callers in the future, in
which case it shouldn't be inlined.  So I'm thinking it would be best
to start out with this as a regular non-inlined function, in
lib/usercopy.c.

Also, copy_to() is a very poor name for a globally-visible helper
function.  Better would be copy_to_user_or_kernel(), although that's
perhaps a bit long.

And the `userbuf' arg should have type bool, yes?


Hi Andrew,

Thank you very much for your reply and suggestion, I agree with you,
I will send v2 later.

Thanks,
Tiezhu


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