This reverts commit 59eab1093a.
The change suppressed EFAULT originating from uiomove(). The deadlock
avoidance mechanism implemented by vn_io_fault1() in the VFS handles
such errors by wiring the user pages and retrying, but this change
caused read() to return early instead. This can result in short I/O,
causing misbehaviour in some applications, and possibly other
consequences.
Until this is resolved somehow, revert the commit.
Approved by: mm
70f51f0e47