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iov: improve copy_iovec_from_user() code generation 

Use the same pattern as the compat version of this code does: instead of
copying the whole array to a kernel buffer and then having a separate
phase of verifying it, just do it one entry at a time, verifying as you
go.

On Jens' /dev/zero readv() test this improves performance by ~6%.

[ This was obviously triggered by Jens' ITER_UBUF updates series ]

Reported-and-tested-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/all/de35d11d-bce7-e976-7372-1f2caf417103@kernel.dk/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2023-03-30 14:53:51 -07:00
parent b9dff2195f
commit 487c20b016
1 changed files with 26 additions and 9 deletions
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35
lib/iov_iter.c
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@ -1735,18 +1735,35 @@ uaccess_end:
}
static int copy_iovec_from_user(struct iovec *iov,
const struct iovec __user *uvec, unsigned long nr_segs)
const struct iovec __user *uiov, unsigned long nr_segs)
{
unsigned long seg;
int ret = -EFAULT;
if (copy_from_user(iov, uvec, nr_segs * sizeof(*uvec)))
if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
return -EFAULT;
for (seg = 0; seg < nr_segs; seg++) {
if ((ssize_t)iov[seg].iov_len < 0)
return -EINVAL;
}
return 0;
do {
void __user *buf;
ssize_t len;
unsafe_get_user(len, &uiov->iov_len, uaccess_end);
unsafe_get_user(buf, &uiov->iov_base, uaccess_end);
/* check for size_t not fitting in ssize_t .. */
if (unlikely(len < 0)) {
ret = -EINVAL;
goto uaccess_end;
}
iov->iov_base = buf;
iov->iov_len = len;
uiov++; iov++;
} while (--nr_segs);
ret = 0;
uaccess_end:
user_access_end();
return ret;
}
struct iovec *iovec_from_user(const struct iovec __user *uvec,
@ -1771,7 +1788,7 @@ struct iovec *iovec_from_user(const struct iovec __user *uvec,
return ERR_PTR(-ENOMEM);
}
if (compat)
if (unlikely(compat))
ret = copy_compat_iovec_from_user(iov, uvec, nr_segs);
else
ret = copy_iovec_from_user(iov, uvec, nr_segs);