[PATCH 1/1] s390/crash: allow multi-segment iterators

Alexander Gordeev
2022-07-06T05:59:52Z

Rework copy_oldmem_page() to allow multi-segment iterators.
Reuse existing iterate_iovec macro as is and only relevant
bits from __iterate_and_advance macro.

Fixes: 49b11524d648 ("s390/crash: add missing iterator advance in copy_oldmem_page())
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---
arch/s390/kernel/crash_dump.c | 65 +++++++++++++++++++++++++++--------
1 file changed, 50 insertions(+), 15 deletions(-)

diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
index 28124d0fa1d5..ac873245d6f0 100644
--- a/arch/s390/kernel/crash_dump.c
+++ b/arch/s390/kernel/crash_dump.c
@@ -210,6 +210,52 @@ static int copy_oldmem_user(void __user *dst, unsigned long src, size_t count)
return 0;
}

+#define iterate_iovec(i, n, base, len, off, __p, STEP) { \
+ size_t off = 0; \
+ size_t skip = i->iov_offset; \
+ do { \
+ len = min(n, __p->iov_len - skip); \
+ if (likely(len)) { \
+ base = __p->iov_base + skip; \
+ len -= (STEP); \
+ off += len; \
+ skip += len; \
+ n -= len; \
+ if (skip < __p->iov_len) \
+ break; \
+ } \
+ __p++; \
+ skip = 0; \
+ } while (n); \
+ i->iov_offset = skip; \
+ n = off; \
+}
+
+#define __iterate_and_advance(i, n, base, len, off, I, K) { \
+ if (unlikely(i->count < n)) \
+ n = i->count; \
+ if (likely(n)) { \
+ if (likely(iter_is_iovec(i))) { \
+ const struct iovec *iov = i->iov; \
+ void __user *base; \
+ size_t len; \
+ iterate_iovec(i, n, base, len, off, \
+ iov, (I)) \
+ i->nr_segs -= iov - i->iov; \
+ i->iov = iov; \
+ } else if (iov_iter_is_kvec(i)) { \
+ const struct kvec *kvec = i->kvec; \
+ void *base; \
+ size_t len; \
+ iterate_iovec(i, n, base, len, off, \
+ kvec, (K)) \
+ i->nr_segs -= kvec - i->kvec; \
+ i->kvec = kvec; \
+ } \
+ i->count -= n; \
+ } \
+}
+
/*
* Copy one page from "oldmem"
*/
@@ -217,25 +263,14 @@ ssize_t copy_oldmem_page(struct iov_iter *iter, unsigned long pfn, size_t csize,
unsigned long offset)
{
unsigned long src;
- int rc;

if (!(iter_is_iovec(iter) || iov_iter_is_kvec(iter)))
return -EINVAL;
- /* Multi-segment iterators are not supported */
- if (iter->nr_segs > 1)
- return -EINVAL;
- if (!csize)
- return 0;
src = pfn_to_phys(pfn) + offset;
-
- /* XXX: pass the iov_iter down to a common function */
- if (iter_is_iovec(iter))
- rc = copy_oldmem_user(iter->iov->iov_base, src, csize);
- else
- rc = copy_oldmem_kernel(iter->kvec->iov_base, src, csize);
- if (rc < 0)
- return rc;
- iov_iter_advance(iter, csize);
+ __iterate_and_advance(iter, csize, base, len, off,
+ ({ copy_oldmem_user(base, src + off, len) < 0 ? csize : 0; }),
+ ({ copy_oldmem_kernel(base, src + off, len) < 0 ? csize : 0; })
+ )
return csize;
}

--
2.34.1