Commit 6d2e5a4a authored by Alexander Gordeev's avatar Alexander Gordeev
Browse files

s390/crash: use static swap buffer for copy_to_user_real() 



Currently a temporary page-size buffer is allocated for copying
oldmem to user space. That limits copy_to_user_real() operation
only to stages when virtual memory is available and still makes
it possible to fail while the system is being dumped.

Instead of reallocating single page on each copy_oldmem_page()
iteration use a statically allocated buffer.

This also paves the way for a further memcpy_real() rework where
no swap buffer is needed altogether.

Acked-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Tested-by: default avatarAlexander Egorenkov <egorenar@linux.ibm.com>
Link: https://lore.kernel.org/r/334ed359680c4d45dd32feb104909f610312ef0f.1658206891.git.agordeev@linux.ibm.com


Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
parent d6da6737

arch/s390/kernel/crash_dump.c

+12 −14
Original line number Diff line number Diff line
@@ -53,6 +53,8 @@ struct save_area { 
};



static LIST_HEAD(dump_save_areas);

static DEFINE_MUTEX(memcpy_real_mutex);

static char memcpy_real_buf[PAGE_SIZE];



/*

 * Allocate a save area
@@ -178,25 +180,21 @@ int copy_oldmem_kernel(void *dst, unsigned long src, size_t count) 
 */

static int copy_to_user_real(void __user *dest, unsigned long src, unsigned long count)

{

	int offs = 0, size, rc;

	char *buf;

	unsigned long offs = 0, size;



	buf = (char *)__get_free_page(GFP_KERNEL);

	if (!buf)

		return -ENOMEM;

	rc = -EFAULT;

	mutex_lock(&memcpy_real_mutex);

	while (offs < count) {

		size = min(PAGE_SIZE, count - offs);

		if (memcpy_real(buf, src + offs, size))

			goto out;

		if (copy_to_user(dest + offs, buf, size))

			goto out;

		if (memcpy_real(memcpy_real_buf, src + offs, size))

			break;

		if (copy_to_user(dest + offs, memcpy_real_buf, size))

			break;

		offs += size;

	}

	rc = 0;

out:

	free_page((unsigned long)buf);

	return rc;

	mutex_unlock(&memcpy_real_mutex);

	if (offs < count)

		return -EFAULT;

	return 0;

}



/*