Rusty Russell <rusty@xxxxxxxxxxxxxxx> writes:
> I'll create some patches and see if it's too ugly to live...
Hmm, with rough userspace testing I managed to get the speed penalty
pretty low.
Here are the two patches, inline:
vringh: handle case where data goes across multiple ranges.
QEMU seems to only use separate memory ranges for ROM vs RAM, but in theory
a single scatterlist element referred to by a vring could cross two ranges,
and thus need to be split into two separate iovec entries.
This causes no measurable slowdown:
Before: (average of 20 runs)
./vringh_test --indirect --eventidx --parallel
real 0m3.236s
After: (average of 20 runs)
./vringh_test --indirect --eventidx --parallel
real 0m3.223s
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 2ba087d..50d37a7 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -91,33 +91,37 @@ static inline ssize_t vringh_iov_xfer(struct vringh_kiov *iov,
return done;
}
-static inline bool check_range(u64 addr, u32 len,
+/* May reduce *len if range is shorter. */
+static inline bool check_range(u64 addr, u32 *len,
struct vringh_range *range,
bool (*getrange)(u64, struct vringh_range *))
{
if (addr < range->start || addr > range->end_incl) {
if (!getrange(addr, range))
- goto bad;
+ return false;
}
BUG_ON(addr < range->start || addr > range->end_incl);
/* To end of memory? */
- if (unlikely(addr + len == 0)) {
+ if (unlikely(addr + *len == 0)) {
if (range->end_incl == -1ULL)
return true;
- goto bad;
+ goto truncate;
}
/* Otherwise, don't wrap. */
- if (unlikely(addr + len < addr))
- goto bad;
- if (unlikely(addr + len - 1 > range->end_incl))
- goto bad;
+ if (addr + *len < addr) {
+ vringh_bad("Wrapping descriptor %u@0x%llx", *len, addr);
+ return false;
+ }
+
+ if (unlikely(addr + *len - 1 > range->end_incl))
+ goto truncate;
return true;
-bad:
- vringh_bad("Malformed descriptor address %u@0x%llx", len, addr);
- return false;
+truncate:
+ *len = range->end_incl + 1 - addr;
+ return true;
}
/* No reason for this code to be inline. */
@@ -205,19 +209,30 @@ __vringh_iov(struct vringh *vrh, u16 i,
for (;;) {
void *addr;
struct vringh_kiov *iov;
+ u32 len;
err = getdesc(&desc, &descs[i]);
if (unlikely(err))
goto fail;
- /* Make sure it's OK, and get offset. */
- if (!check_range(desc.addr, desc.len, &range, getrange)) {
- err = -EINVAL;
- goto fail;
- }
- addr = (void *)(long)desc.addr + range.offset;
-
if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
+ /* Make sure it's OK, and get offset. */
+ len = desc.len;
+ if (!check_range(desc.addr, &len, &range, getrange)) {
+ err = -EINVAL;
+ goto fail;
+ }
+
+ if (len != desc.len) {
+ vringh_bad("Indirect descriptor table across"
+ " ranges: %u@%#llx vs %#llx-%#llx",
+ desc.len, desc.addr, range.start,
+ range.end_incl);
+ err = -EINVAL;
+ goto fail;
+ }
+ addr = (void *)(long)(desc.addr + range.offset);
+
err = move_to_indirect(&up_next, &i, addr, &desc,
&descs, &desc_max);
if (err)
@@ -243,6 +258,15 @@ __vringh_iov(struct vringh *vrh, u16 i,
}
}
+ again:
+ /* Make sure it's OK, and get offset. */
+ len = desc.len;
+ if (!check_range(desc.addr, &len, &range, getrange)) {
+ err = -EINVAL;
+ goto fail;
+ }
+ addr = (void *)(unsigned long)(desc.addr + range.offset);
+
if (unlikely(iov->i == iov->max)) {
err = resize_iovec(iov, gfp);
if (err)
@@ -250,9 +274,15 @@ __vringh_iov(struct vringh *vrh, u16 i,
}
iov->iov[iov->i].iov_base = addr;
- iov->iov[iov->i].iov_len = desc.len;
+ iov->iov[iov->i].iov_len = len;
iov->i++;
+ if (unlikely(len != desc.len)) {
+ desc.len -= len;
+ desc.addr += len;
+ goto again;
+ }
+
if (desc.flags & VRING_DESC_F_NEXT) {
i = desc.next;
} else {
vringh: handle case where indirect descriptors go across multiple ranges.
If a data segment can go across multiple ranges, so can an indirect
descriptor table. This is nastier, so we explicitly slowpath this.
This slows things down a little though.
Before: (average of 20 runs)
./vringh_test --indirect --eventidx --parallel
real 0m3.217s
After: (average of 20 runs)
./vringh_test --indirect --eventidx --parallel
real 0m3.364s
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 50d37a7..5dbf4b1 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -188,17 +188,46 @@ static u16 __cold return_from_indirect(const struct vringh *vrh, int *up_next,
return i;
}
+static int slow_copy(void *dst, const void *src,
+ bool (*getrange)(u64 addr, struct vringh_range *r),
+ struct vringh_range *range,
+ int (*copy)(void *dst, const void *src, size_t len))
+{
+ size_t part, len = sizeof(struct vring_desc);
+
+ do {
+ u64 addr;
+ int err;
+
+ part = len;
+ addr = (u64)(unsigned long)src - range->offset;
+
+ if (!check_range(addr, &part, range, getrange))
+ return -EINVAL;
+
+ err = copy(dst, src, part);
+ if (err)
+ return err;
+
+ dst += part;
+ src += part;
+ len -= part;
+ } while (len);
+ return 0;
+}
+
static inline int
__vringh_iov(struct vringh *vrh, u16 i,
struct vringh_kiov *riov,
struct vringh_kiov *wiov,
bool (*getrange)(u64 addr, struct vringh_range *r),
gfp_t gfp,
- int (*getdesc)(struct vring_desc *dst, const struct vring_desc *s))
+ int (*copy)(void *dst, const void *src, size_t len))
{
int err, count = 0, up_next, desc_max;
struct vring_desc desc, *descs;
- struct vringh_range range = { -1ULL, 0 };
+ struct vringh_range range = { -1ULL, 0 }, slowrange;
+ bool slow = false;
/* We start traversing vring's descriptor table. */
descs = vrh->vring.desc;
@@ -211,7 +240,11 @@ __vringh_iov(struct vringh *vrh, u16 i,
struct vringh_kiov *iov;
u32 len;
- err = getdesc(&desc, &descs[i]);
+ if (unlikely(slow))
+ err = slow_copy(&desc, &descs[i], getrange, &slowrange,
+ copy);
+ else
+ err = copy(&desc, &descs[i], sizeof(desc));
if (unlikely(err))
goto fail;
@@ -223,16 +256,13 @@ __vringh_iov(struct vringh *vrh, u16 i,
goto fail;
}
- if (len != desc.len) {
- vringh_bad("Indirect descriptor table across"
- " ranges: %u@%#llx vs %#llx-%#llx",
- desc.len, desc.addr, range.start,
- range.end_incl);
- err = -EINVAL;
- goto fail;
+ if (unlikely(len != desc.len)) {
+ slow = true;
+ /* We need to save this range to use offset */
+ slowrange = range;
}
- addr = (void *)(long)(desc.addr + range.offset);
+ addr = (void *)(long)(desc.addr + range.offset);
err = move_to_indirect(&up_next, &i, addr, &desc,
&descs, &desc_max);
if (err)
@@ -287,10 +317,11 @@ __vringh_iov(struct vringh *vrh, u16 i,
i = desc.next;
} else {
/* Just in case we need to finish traversing above. */
- if (unlikely(up_next > 0))
+ if (unlikely(up_next > 0)) {
i = return_from_indirect(vrh, &up_next,
&descs, &desc_max);
- else
+ slow = false;
+ } else
break;
}
@@ -479,10 +510,9 @@ static inline int putu16_user(u16 *p, u16 val)
return put_user(val, (__force u16 __user *)p);
}
-static inline int getdesc_user(struct vring_desc *dst,
- const struct vring_desc *src)
+static inline int copydesc_user(void *dst, const void *src, size_t len)
{
- return copy_from_user(dst, (__force void __user *)src, sizeof(*dst)) ?
+ return copy_from_user(dst, (__force void __user *)src, len) ?
-EFAULT : 0;
}
@@ -597,7 +627,7 @@ int vringh_getdesc_user(struct vringh *vrh,
*head = err;
err = __vringh_iov(vrh, *head, (struct vringh_kiov *)riov,
(struct vringh_kiov *)wiov,
- getrange, gfp, getdesc_user);
+ getrange, gfp, copydesc_user);
if (err)
return err;
@@ -711,10 +741,9 @@ static inline int putu16_kern(u16 *p, u16 val)
return 0;
}
-static inline int getdesc_kern(struct vring_desc *dst,
- const struct vring_desc *src)
+static inline int copydesc_kern(void *dst, const void *src, size_t len)
{
- *dst = *src;
+ memcpy(dst, src, len);
return 0;
}
@@ -806,7 +835,7 @@ int vringh_getdesc_kern(struct vringh *vrh,
*head = err;
err = __vringh_iov(vrh, *head, riov, wiov, noop_getrange,
- gfp, getdesc_kern);
+ gfp, copydesc_kern);
if (err)
return err;
diff --git a/tools/virtio/vringh_test.c b/tools/virtio/vringh_test.c
index 01ccaed..bc74c41 100644
--- a/tools/virtio/vringh_test.c
+++ b/tools/virtio/vringh_test.c
@@ -30,14 +30,33 @@ static void never_callback_guest(struct virtqueue *vq)
abort();
}
-static inline bool getrange_iov(u64 addr, struct vringh_range *r)
+static bool getrange_iov(u64 addr, struct vringh_range *r)
{
+ if (addr < (u64)(unsigned long)__user_addr_min - user_addr_offset)
+ return false;
+ if (addr >= (u64)(unsigned long)__user_addr_max - user_addr_offset)
+ return false;
+
r->start = (u64)(unsigned long)__user_addr_min - user_addr_offset;
r->end_incl = (u64)(unsigned long)__user_addr_max - 1 - user_addr_offset;
r->offset = user_addr_offset;
return true;
}
+/* We return single byte ranges. */
+static bool getrange_slow(u64 addr, struct vringh_range *r)
+{
+ if (addr < (u64)(unsigned long)__user_addr_min - user_addr_offset)
+ return false;
+ if (addr >= (u64)(unsigned long)__user_addr_max - user_addr_offset)
+ return false;
+
+ r->start = addr;
+ r->end_incl = r->start;
+ r->offset = user_addr_offset;
+ return true;
+}
+
struct guest_virtio_device {
struct virtio_device vdev;
int to_host_fd;
@@ -75,7 +94,8 @@ static void find_cpus(unsigned int *first, unsigned int *last)
}
}
-static int parallel_test(unsigned long features)
+static int parallel_test(unsigned long features,
+ bool (*getrange)(u64 addr, struct vringh_range *r))
{
void *host_map, *guest_map;
int fd, mapsize, to_guest[2], to_host[2];
@@ -144,7 +164,7 @@ static int parallel_test(unsigned long features)
wiov.max = ARRAY_SIZE(host_wiov);
wiov.allocated = false;
- err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange_iov,
+ err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange,
&head, GFP_KERNEL);
if (err == 0) {
char buf[128];
@@ -349,6 +369,7 @@ int main(int argc, char *argv[])
int err;
unsigned i;
void *ret;
+ bool (*getrange)(u64 addr, struct vringh_range *r) = getrange_iov;
vdev.features[0] = 0;
@@ -362,8 +383,13 @@ int main(int argc, char *argv[])
argv++;
}
+ if (argv[1] && strcmp(argv[1], "--slow") == 0) {
+ getrange = getrange_slow;
+ argv++;
+ }
+
if (argv[1] && strcmp(argv[1], "--parallel") == 0)
- return parallel_test(vdev.features[0]);
+ return parallel_test(vdev.features[0], getrange);
if (posix_memalign(&__user_addr_min, PAGE_SIZE, USER_MEM) != 0)
abort();
@@ -382,7 +408,7 @@ int main(int argc, char *argv[])
vrh.vring.desc, vrh.vring.avail, vrh.vring.used);
/* No descriptor to get yet... */
- err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange_iov,
+ err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange,
&head, GFP_KERNEL);
if (err != 0)
errx(1, "vringh_getdesc_user: %i", err);
@@ -410,7 +436,7 @@ int main(int argc, char *argv[])
wiov.max = ARRAY_SIZE(host_wiov);
wiov.allocated = false;
- err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange_iov,
+ err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange,
&head, GFP_KERNEL);
if (err != 1)
errx(1, "vringh_getdesc_user: %i", err);
@@ -418,9 +444,17 @@ int main(int argc, char *argv[])
assert(riov.max == 1);
assert(riov.iov[0].iov_base == __user_addr_max - 1);
assert(riov.iov[0].iov_len == 1);
- assert(wiov.max == 1);
- assert(wiov.iov[0].iov_base == __user_addr_max - 3);
- assert(wiov.iov[0].iov_len == 2);
+ if (getrange != getrange_slow) {
+ assert(wiov.max == 1);
+ assert(wiov.iov[0].iov_base == __user_addr_max - 3);
+ assert(wiov.iov[0].iov_len == 2);
+ } else {
+ assert(wiov.max == 2);
+ assert(wiov.iov[0].iov_base == __user_addr_max - 3);
+ assert(wiov.iov[0].iov_len == 1);
+ assert(wiov.iov[1].iov_base == __user_addr_max - 2);
+ assert(wiov.iov[1].iov_len == 1);
+ }
err = vringh_iov_pull_user(&riov, buf, 5);
if (err != 1)
@@ -434,7 +468,7 @@ int main(int argc, char *argv[])
if (err != 2)
errx(1, "vringh_iov_push_user: %i", err);
assert(memcmp(__user_addr_max - 3, "bc", 2) == 0);
- assert(wiov.i == 1);
+ assert(wiov.i == wiov.max);
assert(vringh_iov_push_user(&wiov, buf, 5) == 0);
/* Host is done. */
@@ -477,14 +511,17 @@ int main(int argc, char *argv[])
wiov.max = ARRAY_SIZE(host_wiov);
wiov.allocated = false;
- err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange_iov,
+ err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange,
&head, GFP_KERNEL);
if (err != 1)
errx(1, "vringh_getdesc_user: %i", err);
assert(riov.allocated);
assert(riov.iov != host_riov);
- assert(riov.max == RINGSIZE);
+ if (getrange != getrange_slow)
+ assert(riov.max == RINGSIZE);
+ else
+ assert(riov.max == RINGSIZE * USER_MEM/4);
assert(!wiov.allocated);
assert(wiov.max == 0);
@@ -567,7 +604,7 @@ int main(int argc, char *argv[])
wiov.max = ARRAY_SIZE(host_wiov);
wiov.allocated = false;
- err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange_iov,
+ err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange,
&head, GFP_KERNEL);
if (err != 1)
errx(1, "vringh_getdesc_user: %i", err);
@@ -575,7 +612,10 @@ int main(int argc, char *argv[])
if (head != n)
errx(1, "vringh_getdesc_user: head %i not %i", head, n);
- assert(riov.max == 7);
+ if (getrange != getrange_slow)
+ assert(riov.max == 7);
+ else
+ assert(riov.max == 28);
assert(riov.allocated);
err = vringh_iov_pull_user(&riov, buf, 29);
assert(err == 28);
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