linux.git/arch/um/os-Linux, branch vsnprintf

um: move thread info into task

2024-11-12T13:50:31+00:00

This selects the THREAD_INFO_IN_TASK option for UM and changes the way
that the current task is discovered. This is trivial though, as UML
already tracks the current task in cpu_tasks[] and this can be used to
retrieve it.

Also remove the signal handler code that copies the thread information
into the IRQ stack. It is obsolete now, which also means that the
mentioned race condition cannot happen anymore.

Signed-off-by: Benjamin Berg 
Reviewed-by: Hajime Tazaki 
Link: https://patch.msgid.link/20241111102910.46512-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: remove broken double fault detection

2024-11-07T16:36:31+00:00

The show_stack function had some code to detect double faults. However,
the logic is wrong and it would e.g. trigger if a WARNING happened
inside an IRQ.

Remove it without trying to add a new logic. The current behaviour,
which will just fault repeatedly until the IRQ stack is used up and the
host kills UML, seems to be good enough.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241103150506.1367695-5-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: remove file sync for stub data

2024-11-07T16:36:30+00:00

There is no need to sync the stub code to "disk" for the other process
to see the correct memory. Drop the fsync there and remove the helper
function.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241103150506.1367695-3-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: always include kconfig.h and compiler-version.h

2024-11-07T16:36:30+00:00

Since commit a95b37e20db9 ("kbuild: get  out of
") we can safely include these files in userspace code.
Doing so simplifies matters as options do not need to be exported via
asm-offsets.h anymore.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241103150506.1367695-2-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: set DONTDUMP and DONTFORK flags on KASAN shadow memory

2024-11-07T16:36:30+00:00

There is no point in either dumping the KASAN shadow memory or doing
copy-on-write after a fork on these memory regions.

This considerably speeds up coredump generation.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241103150506.1367695-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: Set parent-death signal for write_sigio thread/process

2024-10-25T09:34:55+00:00

The write_sigio thread is not really a traditional thread. Set
the parent-death signal for it to ensure that it will be killed
if the UML kernel dies unexpectedly without proper cleanup.

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20241024142828.2612828-4-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg

um: Add os_set_pdeathsig helper function

2024-10-25T09:34:54+00:00

This helper can be used to set the parent-death signal of the calling
process to SIGKILL to ensure that the process will be killed if the
UML kernel dies unexpectedly without proper cleanup. This helper will
be used in the follow-up patches.

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20241024142828.2612828-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg

um: remove PATH_MAX use

2024-10-24T07:52:51+00:00

Evidently, PATH_MAX isn't always defined, at least not via .
Simply remove the use and replace it by a constant 4k. As stat::st_size
is zero for /proc/self/exe we can't even size it automatically, and it
seems unlikely someone's going to try to run UML with such a path.

Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-kbuild-all/202410240553.gYNIXN8i-lkp@intel.com/
Fixes: 031acdcfb566 ("um: restore process name")
Signed-off-by: Johannes Berg

um: switch to regset API and depend on XSTATE

2024-10-23T10:13:16+00:00

The PTRACE_GETREGSET API has now existed since Linux 2.6.33. The XSAVE
CPU feature should also be sufficiently common to be able to rely on it.

With this, define our internal FP state to be the hosts XSAVE data. Add
discovery for the hosts XSAVE size and place the FP registers at the end
of task_struct so that we can adjust the size at runtime.

Next we can implement the regset API on top and update the signal
handling as well as ptrace APIs to use them. Also switch coredump
creation to use the regset API and finally set HAVE_ARCH_TRACEHOOK.

This considerably improves the signal frames. Previously they might not
have contained all the registers (i386) and also did not have the
sizes and magic values set to the correct values to permit userspace to
decode the frame.

As a side effect, this will permit UML to run on hosts with newer CPU
extensions (such as AMX) that need even more register state.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241023094120.4083426-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

um: insert scheduler ticks when userspace does not yield

2024-10-23T07:52:49+00:00

In time-travel mode userspace can do a lot of work without any time
passing. Unfortunately, this can result in OOM situations as the RCU
core code will never be run.

Work around this by keeping track of userspace processes that do not
yield for a lot of operations. When this happens, insert a jiffie into
the sched_clock clock to account time against the process and cause the
bookkeeping to run.

As sched_clock is used for tracing, it is useful to keep it in sync
between the different VMs. As such, try to remove added ticks again when
the actual clock ticks.

Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241010142537.1134685-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg