s390/crash: support multi-segment iterators

Make it possible to handle not only single-, but also multi-
segment iterators in copy_oldmem_iter() callback. Change the
semantics of called functions to match the iterator model -
instead of an error code the exact number of bytes copied is
returned.

The swap page used to copy data to user space is adopted for
kernel space too. That does not bring any performance impact.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Fixes: cc02e6e21aa5 ("s390/crash: add missing iterator advance in copy_oldmem_page()")
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Tested-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Link: https://lore.kernel.org/r/5af6da3a0bffe48a90b0b7139ecf6a818b2d18e8.1658206891.git.agordeev@linux.ibm.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 23 insertions, 35 deletions

diff --git a/drivers/s390/char/zcore.c b/drivers/s390/char/zcore.c
index 92b32ce645b9..f6da215ccf9f 100644
--- a/drivers/s390/char/zcore.c
+++ b/drivers/s390/char/zcore.c
@@ -17,6 +17,7 @@
 #include <linux/debugfs.h>
 #include <linux/panic_notifier.h>
 #include <linux/reboot.h>
+#include <linux/uio.h>
 
 #include <asm/asm-offsets.h>
 #include <asm/ipl.h>
@@ -54,38 +55,37 @@ static DEFINE_MUTEX(hsa_buf_mutex);
 static char hsa_buf[PAGE_SIZE] __aligned(PAGE_SIZE);
 
 /*
- * Copy memory from HSA to user memory (not reentrant):
+ * Copy memory from HSA to iterator (not reentrant):
  *
- * @dest:  User buffer where memory should be copied to
+ * @iter:  Iterator where memory should be copied to
  * @src:   Start address within HSA where data should be copied
  * @count: Size of buffer, which should be copied
  */
-int memcpy_hsa_user(void __user *dest, unsigned long src, size_t count)
+size_t memcpy_hsa_iter(struct iov_iter *iter, unsigned long src, size_t count)
 {
-	unsigned long offset, bytes;
+	size_t bytes, copied, res = 0;
+	unsigned long offset;
 
 	if (!hsa_available)
-		return -ENODATA;
+		return 0;
 
 	mutex_lock(&hsa_buf_mutex);
 	while (count) {
 		if (sclp_sdias_copy(hsa_buf, src / PAGE_SIZE + 2, 1)) {
 			TRACE("sclp_sdias_copy() failed\n");
-			mutex_unlock(&hsa_buf_mutex);
-			return -EIO;
+			break;
 		}
 		offset = src % PAGE_SIZE;
 		bytes = min(PAGE_SIZE - offset, count);
-		if (copy_to_user(dest, hsa_buf + offset, bytes)) {
-			mutex_unlock(&hsa_buf_mutex);
-			return -EFAULT;
-		}
-		src += bytes;
-		dest += bytes;
-		count -= bytes;
+		copied = copy_to_iter(hsa_buf + offset, bytes, iter);
+		count -= copied;
+		src += copied;
+		res += copied;
+		if (copied < bytes)
+			break;
 	}
 	mutex_unlock(&hsa_buf_mutex);
-	return 0;
+	return res;
 }
 
 /*
@@ -95,28 +95,16 @@ int memcpy_hsa_user(void __user *dest, unsigned long src, size_t count)
  * @src:   Start address within HSA where data should be copied
  * @count: Size of buffer, which should be copied
  */
-int memcpy_hsa_kernel(void *dest, unsigned long src, size_t count)
+static inline int memcpy_hsa_kernel(void *dst, unsigned long src, size_t count)
 {
-	unsigned long offset, bytes;
+	struct iov_iter iter;
+	struct kvec kvec;
 
-	if (!hsa_available)
-		return -ENODATA;
-
-	mutex_lock(&hsa_buf_mutex);
-	while (count) {
-		if (sclp_sdias_copy(hsa_buf, src / PAGE_SIZE + 2, 1)) {
-			TRACE("sclp_sdias_copy() failed\n");
-			mutex_unlock(&hsa_buf_mutex);
-			return -EIO;
-		}
-		offset = src % PAGE_SIZE;
-		bytes = min(PAGE_SIZE - offset, count);
-		memcpy(dest, hsa_buf + offset, bytes);
-		src += bytes;
-		dest += bytes;
-		count -= bytes;
-	}
-	mutex_unlock(&hsa_buf_mutex);
+	kvec.iov_base = dst;
+	kvec.iov_len = count;
+	iov_iter_kvec(&iter, WRITE, &kvec, 1, count);
+	if (memcpy_hsa_iter(&iter, src, count) < count)
+		return -EIO;
 	return 0;
 }