On Tuesday 24 Nov 2020 at 15:50:32 (+0000), Will Deacon wrote: > Asymmetric systems may not offer the same level of userspace ISA support > across all CPUs, meaning that some applications cannot be executed by > some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do > not feature support for 32-bit applications on both clusters. > > Although userspace can carefully manage the affinity masks for such > tasks, one place where it is particularly problematic is execve() > because the CPU on which the execve() is occurring may be incompatible > with the new application image. In such a situation, it is desirable to > restrict the affinity mask of the task and ensure that the new image is > entered on a compatible CPU. From userspace's point of view, this looks > the same as if the incompatible CPUs have been hotplugged off in its > affinity mask. > > In preparation for restricting the affinity mask for compat tasks on > arm64 systems without uniform support for 32-bit applications, introduce > a restrict_cpus_allowed_ptr(), which allows the current affinity mask > for a task to be shrunk to the intersection of a parameter mask. > > Signed-off-by: Will Deacon <will@xxxxxxxxxx> Reviewed-by: Quentin Perret <qperret@xxxxxxxxxx> Thanks, Quentin
