UML is using an obsolete itimer call for
all timers and "polls" for kernel space timer firing
in its userspace portion resulting in a long list
of bugs and incorrect behaviour(s). It also uses
ITIMER_VIRTUAL for its timer which results in the
timer being dependent on it running and the cpu
load.

This patch fixes this by moving to posix high resolution
timers firing off CLOCK_MONOTONIC and relaying the timer
correctly to the UML userspace.

Fixes:
 - crashes when hosts suspends/resumes
 - broken userspace timers - effecive ~40Hz instead
   of what they should be. Note - this modifies skas behavior
   by no longer setting an itimer per clone(). Timer events
   are relayed instead.
 - kernel network packet scheduling disciplines
 - tcp behaviour especially under load
 - various timer related corner cases

Finally, overall responsiveness of userspace is better.

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Anton Ivanov <aivanov@brocade.com>
[rw: massaged commit message]
Signed-off-by: Richard Weinberger <richard@nod.at>

since GFP_KERNEL with GFP_ATOMIC while spinlock is held,
as code while holding a spinlock should be atomic.
GFP_KERNEL may sleep and can cause deadlock,
where as GFP_ATOMIC may fail but certainly avoids deadlockdex f70dd54..d898f6c 100644

Signed-off-by: Saurabh Sengar <saurabh.truth@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

If UML runs on the host side out of memory, report this
condition more nicely.

Signed-off-by: Richard Weinberger <richard@nod.at>

We can use __NR_syscall_max.

Signed-off-by: Richard Weinberger <richard@nod.at>

To support changing syscall numbers we have to store
it after syscall_trace_enter().

Signed-off-by: Richard Weinberger <richard@nod.at>

...such that processes within UML can do a ptrace(PTRACE_OLDSETOPTIONS, ...)

Signed-off-by: Richard Weinberger <richard@nod.at>

We have to exclude memory locations <= PAGE_SIZE from
the condition and let the kernel mode fault path catch it.
Otherwise a kernel NULL pointer exception will be reported
as a kernel user space access.

Fixes: d2313084e2c (um: Catch unprotected user memory access)
Signed-off-by: Richard Weinberger <richard@nod.at>

If UML is executing a helper program it is using
waitpid() with the __WCLONE flag to wait for the program
as the helper is executed from a clone()'ed thread.
While using __WCLONE is perfectly fine for clone()'ed
childs it won't detect terminated childs if the helper
has issued an execve().

We have to use __WALL to wait for both clone()'ed and
regular childs to detect the termination before and
after an execve().

Reported-and-tested-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

Commit 30b11ee9a (um: Remove copy&paste code from init.h)
uncovered an issue wrt. out-of-tree builds.
For out-of-tree builds, we must not rely on relative paths.
Before 30b11ee9a it worked by chance as no host code included
generated header files.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Richard Weinberger <richard@nod.at>

Pull strscpy string copy function implementation from Chris Metcalf.

Chris sent this during the merge window, but I waffled back and forth on
the pull request, which is why it's going in only now.

The new "strscpy()" function is definitely easier to use and more secure
than either strncpy() or strlcpy(), both of which are horrible nasty
interfaces that have serious and irredeemable problems.

strncpy() has a useless return value, and doesn't NUL-terminate an
overlong result.  To make matters worse, it pads a short result with
zeroes, which is a performance disaster if you have big buffers.

strlcpy(), by contrast, is a mis-designed "fix" for strlcpy(), lacking
the insane NUL padding, but having a differently broken return value
which returns the original length of the source string.  Which means
that it will read characters past the count from the source buffer, and
you have to trust the source to be properly terminated.  It also makes
error handling fragile, since the test for overflow is unnecessarily
subtle.

strscpy() avoids both these problems, guaranteeing the NUL termination
(but not excessive padding) if the destination size wasn't zero, and
making the overflow condition very obvious by returning -E2BIG.  It also
doesn't read past the size of the source, and can thus be used for
untrusted source data too.

So why did I waffle about this for so long?

Every time we introduce a new-and-improved interface, people start doing
these interminable series of trivial conversion patches.

And every time that happens, somebody does some silly mistake, and the
conversion patch to the improved interface actually makes things worse.
Because the patch is mindnumbing and trivial, nobody has the attention
span to look at it carefully, and it's usually done over large swatches
of source code which means that not every conversion gets tested.

So I'm pulling the strscpy() support because it *is* a better interface.
But I will refuse to pull mindless conversion patches.  Use this in
places where it makes sense, but don't do trivial patches to fix things
that aren't actually known to be broken.

* 'strscpy' of git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile:
  tile: use global strscpy() rather than private copy
  string: provide strscpy()
  Make asm/word-at-a-time.h available on all architectures