[PATCH v2] kexec: copy only happens before uchunk goes to zero

[yang.zhang]

From: "yang.zhang" <yang.zhang@xxxxxxxxxxxx>

When load segments, all of the copying and the rest
only happens before uchunk goes to zero.

Signed-off-by: yang.zhang <yang.zhang@xxxxxxxxxxxx>

---
v1 -> v2:
- Only copy before uchunk goes to zero

V1: https://lore.kernel.org/lkml/20240130101802.23850-1-gaoshanliukou@xxxxxxx/
---
 kernel/kexec_core.c | 44 ++++++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index d08fc7b5db97..2fc3d0e3715a 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image,
 				PAGE_SIZE - (maddr & ~PAGE_MASK));
 		uchunk = min(ubytes, mchunk);
 
-		/* For file based kexec, source pages are in kernel memory */
-		if (image->file_mode)
-			memcpy(ptr, kbuf, uchunk);
-		else
-			result = copy_from_user(ptr, buf, uchunk);
+		if (uchunk) {
+			/* For file based kexec, source pages are in kernel memory */
+			if (image->file_mode)
+				memcpy(ptr, kbuf, uchunk);
+			else
+				result = copy_from_user(ptr, buf, uchunk);
+			ubytes -= uchunk;
+			if (image->file_mode)
+				kbuf += uchunk;
+			else
+				buf += uchunk;
+		}
 		kunmap_local(ptr);
 		if (result) {
 			result = -EFAULT;
 			goto out;
 		}
-		ubytes -= uchunk;
 		maddr  += mchunk;
-		if (image->file_mode)
-			kbuf += mchunk;
-		else
-			buf += mchunk;
 		mbytes -= mchunk;
 
 		cond_resched();
@@ -866,11 +868,18 @@ static int kimage_load_crash_segment(struct kimage *image,
 			memset(ptr + uchunk, 0, mchunk - uchunk);
 		}
 
-		/* For file based kexec, source pages are in kernel memory */
-		if (image->file_mode)
-			memcpy(ptr, kbuf, uchunk);
-		else
-			result = copy_from_user(ptr, buf, uchunk);
+		if (uchunk) {
+			/* For file based kexec, source pages are in kernel memory */
+			if (image->file_mode)
+				memcpy(ptr, kbuf, uchunk);
+			else
+				result = copy_from_user(ptr, buf, uchunk);
+			ubytes -= uchunk;
+			if (image->file_mode)
+				kbuf += uchunk;
+			else
+				buf += uchunk;
+		}
 		kexec_flush_icache_page(page);
 		kunmap_local(ptr);
 		arch_kexec_pre_free_pages(page_address(page), 1);
@@ -878,12 +887,7 @@ static int kimage_load_crash_segment(struct kimage *image,
 			result = -EFAULT;
 			goto out;
 		}
-		ubytes -= uchunk;
 		maddr  += mchunk;
-		if (image->file_mode)
-			kbuf += mchunk;
-		else
-			buf += mchunk;
 		mbytes -= mchunk;
 
 		cond_resched();
-- 
2.25.1