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Subject[PATCH v3 2/3] s390/crash: use static swap buffer for copy_to_user_real()
Date
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.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---
arch/s390/kernel/crash_dump.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
index 8d7332d4444c..fd9fe93e48b6 100644
--- a/arch/s390/kernel/crash_dump.c
+++ b/arch/s390/kernel/crash_dump.c
@@ -53,6 +53,7 @@ struct save_area {
};

static LIST_HEAD(dump_save_areas);
+static char memcpy_real_buf[PAGE_SIZE];

/*
* Allocate a save area
@@ -179,23 +180,18 @@ 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;

- buf = (char *)__get_free_page(GFP_KERNEL);
- if (!buf)
- return -ENOMEM;
rc = -EFAULT;
while (offs < count) {
size = min(PAGE_SIZE, count - offs);
- if (memcpy_real(buf, src + offs, size))
+ if (memcpy_real(memcpy_real_buf, src + offs, size))
goto out;
- if (copy_to_user(dest + offs, buf, size))
+ if (copy_to_user(dest + offs, memcpy_real_buf, size))
goto out;
offs += size;
}
rc = 0;
out:
- free_page((unsigned long)buf);
return rc;
}

--
2.34.1
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