linux.git/arch/um/kernel/process.c, branch v7.0

um: Add initial SMP support

2025-10-27T15:41:15+00:00

Add initial symmetric multi-processing (SMP) support to UML. With
this support enabled, users can tell UML to start multiple virtual
processors, each represented as a separate host thread.

In UML, kthreads and normal threads (when running in kernel mode)
can be scheduled and executed simultaneously on different virtual
processors. However, the userspace code of normal threads still
runs within their respective single-threaded stubs.

That is, SMP support is currently available both within the kernel
and across different processes, but still remains limited within
threads of the same process in userspace.

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20251027001815.1666872-6-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg

um: Determine sleep based on need_resched()

2025-10-27T15:41:15+00:00

With SMP and NO_HZ enabled, the CPU may still need to sleep even
if the timer is disarmed. Switch to deciding whether to sleep based
on pending resched. Additionally, because disabling IRQs does not
block SIGALRM, it is also necessary to check for any pending timer
alarms. This is a preparation for adding SMP support.

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20251027001815.1666872-4-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg

um: Do not disable kmalloc in initial_thread_cb()

2025-10-27T15:41:14+00:00

Currently, initial_thread_cb() temporarily disables kmalloc when
it invokes the callback, allowing the callback to bypass kmalloc.
This is unnecessary for the current users of initial_thread_cb(),
and we should avoid memory allocations that are not under the
control of the UML kernel. Therefore, let's stop temporarily
disabling kmalloc in initial_thread_cb().

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20251027001815.1666872-2-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg

um: init cpu_tasks[] earlier

2025-10-27T14:05:50+00:00

This is currently done in uml_finishsetup(), but e.g. with
KCOV enabled we'll crash because some init code can call
into e.g. memparse(), which has coverage annotations, and
then the checks in check_kcov_mode() crash because current
is NULL.

Simply initialize the cpu_tasks[] array statically, which
fixes the crash. For the later SMP work, it seems to have
not really caused any problems yet, but initialize all of
the entries anyway.

Link: https://patch.msgid.link/20250924113214.c76cd74d0583.I974f691ebb1a2b47915bd2b04cc38e5263b9447f@changeid
Signed-off-by: Johannes Berg

arch: copy_thread: pass clone_flags as u64

2025-09-01T13:31:34+00:00

With the introduction of clone3 in commit 7f192e3cd316 ("fork: add
clone3") the effective bit width of clone_flags on all architectures was
increased from 32-bit to 64-bit, with a new type of u64 for the flags.
However, for most consumers of clone_flags the interface was not
changed from the previous type of unsigned long.

While this works fine as long as none of the new 64-bit flag bits
(CLONE_CLEAR_SIGHAND and CLONE_INTO_CGROUP) are evaluated, this is still
undesirable in terms of the principle of least surprise.

Thus, this commit fixes all relevant interfaces of the copy_thread
function that is called from copy_process to consistently pass
clone_flags as u64, so that no truncation to 32-bit integers occurs on
32-bit architectures.

Signed-off-by: Simon Schuster 
Link: https://lore.kernel.org/20250901-nios2-implement-clone3-v2-3-53fcf5577d57@siemens-energy.com
Fixes: c5febea0956fd387 ("fork: Pass struct kernel_clone_args into copy_thread")
Acked-by: Guo Ren (Alibaba Damo Academy) 
Acked-by: Andreas Larsson  # sparc
Acked-by: David Hildenbrand 
Acked-by: Geert Uytterhoeven  # m68k
Reviewed-by: Arnd Bergmann 
Signed-off-by: Christian Brauner

um: Re-evaluate thread flags repeatedly

2025-07-11T06:49:02+00:00

The thread flags may change during their processing.
For example a task_work can queue a new signal to be sent.
This signal should be delivered before returning to usespace again.

Evaluate the flags repeatedly similar to other architectures.

Signed-off-by: Thomas Weißschuh 
Reviewed-by: Nam Cao 
Link: https://patch.msgid.link/20250704-uml-thread_flags-v1-1-0e293fd8d627@linutronix.de
Signed-off-by: Johannes Berg

um: avoid copying FP state from init_task

2025-02-12T22:40:38+00:00

The init_task instance of struct task_struct is statically allocated and
does not contain the dynamic area for the userspace FP registers. As
such, limit the copy to the valid area of init_task and fill the rest
with zero.

Note that the FP state is only needed for userspace, and as such it is
entirely reasonable for init_task to not contain it.

Reported-by: Brian Norris 
Closes: https://lore.kernel.org/Z1ySXmjZm-xOqk90@google.com
Fixes: 3f17fed21491 ("um: switch to regset API and depend on XSTATE")
Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20241217202745.1402932-3-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg 
Signed-off-by: Richard Weinberger

um: Remove unused user_context function

2025-01-10T12:49:57+00:00

It's no longer used since commit 6aa802ce6acc ("uml: throw out
CHOOSE_MODE").

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20241128083137.2219830-10-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg

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: 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