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Subject[PATCH] vringh: iterate on iotlb_translate to handle large translations
Date
iotlb_translate() can return -ENOBUFS if the bio_vec is not big enough
to contain all the ranges for translation.
This can happen for example if the VMM maps a large bounce buffer,
without using hugepages, that requires more than 16 ranges to translate
the addresses.

To handle this case, let's extend iotlb_translate() to also return the
number of bytes successfully translated.
In copy_from_iotlb()/copy_to_iotlb() loops by calling iotlb_translate()
several times until we complete the translation.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
drivers/vhost/vringh.c | 78 ++++++++++++++++++++++++++++++------------
1 file changed, 56 insertions(+), 22 deletions(-)

diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index eab55accf381..11f59dd06a74 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -1095,7 +1095,8 @@ EXPORT_SYMBOL(vringh_need_notify_kern);
#if IS_REACHABLE(CONFIG_VHOST_IOTLB)

static int iotlb_translate(const struct vringh *vrh,
- u64 addr, u64 len, struct bio_vec iov[],
+ u64 addr, u64 len, u64 *translated,
+ struct bio_vec iov[],
int iov_size, u32 perm)
{
struct vhost_iotlb_map *map;
@@ -1136,43 +1137,76 @@ static int iotlb_translate(const struct vringh *vrh,

spin_unlock(vrh->iotlb_lock);

+ if (translated)
+ *translated = min(len, s);
+
return ret;
}

static inline int copy_from_iotlb(const struct vringh *vrh, void *dst,
void *src, size_t len)
{
- struct iov_iter iter;
- struct bio_vec iov[16];
- int ret;
+ u64 total_translated = 0;

- ret = iotlb_translate(vrh, (u64)(uintptr_t)src,
- len, iov, 16, VHOST_MAP_RO);
- if (ret < 0)
- return ret;
+ while (total_translated < len) {
+ struct bio_vec iov[16];
+ struct iov_iter iter;
+ u64 translated;
+ int ret;

- iov_iter_bvec(&iter, READ, iov, ret, len);
+ ret = iotlb_translate(vrh, (u64)(uintptr_t)src,
+ len - total_translated, &translated,
+ iov, ARRAY_SIZE(iov), VHOST_MAP_RO);
+ if (ret == -ENOBUFS)
+ ret = ARRAY_SIZE(iov);
+ else if (ret < 0)
+ return ret;

- ret = copy_from_iter(dst, len, &iter);
+ iov_iter_bvec(&iter, READ, iov, ret, translated);

- return ret;
+ ret = copy_from_iter(dst, translated, &iter);
+ if (ret < 0)
+ return ret;
+
+ src += translated;
+ dst += translated;
+ total_translated += translated;
+ }
+
+ return total_translated;
}

static inline int copy_to_iotlb(const struct vringh *vrh, void *dst,
void *src, size_t len)
{
- struct iov_iter iter;
- struct bio_vec iov[16];
- int ret;
+ u64 total_translated = 0;

- ret = iotlb_translate(vrh, (u64)(uintptr_t)dst,
- len, iov, 16, VHOST_MAP_WO);
- if (ret < 0)
- return ret;
+ while (total_translated < len) {
+ struct bio_vec iov[16];
+ struct iov_iter iter;
+ u64 translated;
+ int ret;
+
+ ret = iotlb_translate(vrh, (u64)(uintptr_t)dst,
+ len - total_translated, &translated,
+ iov, ARRAY_SIZE(iov), VHOST_MAP_WO);
+ if (ret == -ENOBUFS)
+ ret = ARRAY_SIZE(iov);
+ else if (ret < 0)
+ return ret;

- iov_iter_bvec(&iter, WRITE, iov, ret, len);
+ iov_iter_bvec(&iter, WRITE, iov, ret, translated);
+
+ ret = copy_to_iter(src, translated, &iter);
+ if (ret < 0)
+ return ret;
+
+ src += translated;
+ dst += translated;
+ total_translated += translated;
+ }

- return copy_to_iter(src, len, &iter);
+ return total_translated;
}

static inline int getu16_iotlb(const struct vringh *vrh,
@@ -1183,7 +1217,7 @@ static inline int getu16_iotlb(const struct vringh *vrh,
int ret;

/* Atomic read is needed for getu16 */
- ret = iotlb_translate(vrh, (u64)(uintptr_t)p, sizeof(*p),
+ ret = iotlb_translate(vrh, (u64)(uintptr_t)p, sizeof(*p), NULL,
&iov, 1, VHOST_MAP_RO);
if (ret < 0)
return ret;
@@ -1204,7 +1238,7 @@ static inline int putu16_iotlb(const struct vringh *vrh,
int ret;

/* Atomic write is needed for putu16 */
- ret = iotlb_translate(vrh, (u64)(uintptr_t)p, sizeof(*p),
+ ret = iotlb_translate(vrh, (u64)(uintptr_t)p, sizeof(*p), NULL,
&iov, 1, VHOST_MAP_WO);
if (ret < 0)
return ret;
--
2.36.1
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