bybrooklyn/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-04-18 06:44:00 -04:00
Code Issues Packages Projects Releases Wiki Activity

ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems

Browse Source 
On UP systems, only a single task can be 'current' at the same time,
which means we can use a global variable to track it. This means we can
also enable THREAD_INFO_IN_TASK for those systems, as in that case,
thread_info is accessed via current rather than the other way around,
removing the need to store thread_info at the base of the task stack.
This, in turn, permits us to enable IRQ stacks and vmap'ed stacks on UP
systems as well.

To partially mitigate the performance overhead of this arrangement, use
a ADD/ADD/LDR sequence with the appropriate PC-relative group
relocations to load the value of current when needed. This means that
accessing current will still only require a single load as before,
avoiding the need for a literal to carry the address of the global
variable in each function. However, accessing thread_info will now
require this load as well.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
This commit is contained in:
Ard Biesheuvel
2021-11-24 14:08:11 +01:00
parent c275591037
commit 9c46929e79
12 changed files with 116 additions and 92 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
arch/arm/kernel/smp.c
View File

@@ -403,6 +403,17 @@ static void smp_store_cpu_info(unsigned int cpuid)
check_cpu_icache_size(cpuid);
}
static void set_current(struct task_struct *cur)
{
if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO) && !is_smp()) {
__current = cur;
return;
}
/* Set TPIDRURO */
asm("mcr p15, 0, %0, c13, c0, 3" :: "r"(cur) : "memory");
}
/*
* This is the secondary CPU boot entry. We're using this CPUs
* idle thread stack, but a set of temporary page tables.