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MIPS: Fix idle VS timer enqueue

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MIPS re-enables interrupts on its idle routine and performs
a TIF_NEED_RESCHED check afterwards before putting the CPU to sleep.

The IRQs firing between the check and the 'wait' instruction may set the
TIF_NEED_RESCHED flag. In order to deal with this possible race, IRQs
interrupting __r4k_wait() rollback their return address to the
beginning of __r4k_wait() so that TIF_NEED_RESCHED is checked
again before going back to sleep.

However idle IRQs can also queue timers that may require a tick
reprogramming through a new generic idle loop iteration but those timers
would go unnoticed here because __r4k_wait() only checks
TIF_NEED_RESCHED. It doesn't check for pending timers.

Fix this with fast-forwarding idle IRQs return address to the end of the
idle routine instead of the beginning, so that the generic idle loop
handles both TIF_NEED_RESCHED and pending timers.

CONFIG_CPU_MICROMIPS has been removed along with the nop instructions.
There, NOPs are 2 byte in size, so change the code with 3 _ssnop which are
always 4 byte and remove the ifdef. Added ehb to make sure the hazard
is always cleared.

Fixes: c65a5480ff ("[MIPS] Fix potential latency problem due to non-atomic cpu_wait.")
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
This commit is contained in:
Marco Crivellari 2025-04-03 18:11:42 +02:00 committed by Thomas Bogendoerfer
parent 0af2f6be1b
commit 56651128e2
3 changed files with 37 additions and 35 deletions
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3
arch/mips/include/asm/idle.h
View File

@ -6,8 +6,7 @@
#include <linux/linkage.h> #include <linux/linkage.h>
extern void (*cpu_wait)(void); extern void (*cpu_wait)(void);
extern void r4k_wait(void); extern asmlinkage void r4k_wait(void);
extern asmlinkage void __r4k_wait(void);
extern void r4k_wait_irqoff(void); extern void r4k_wait_irqoff(void);
static inline int using_rollback_handler(void) static inline int using_rollback_handler(void)

62
arch/mips/kernel/genex.S
View File

@ -104,42 +104,52 @@ handle_vcei:
__FINIT __FINIT
.align 5 /* 32 byte rollback region */ /* Align to 32 bytes for the maximum idle interrupt region size. */
LEAF(__r4k_wait) .align 5
.set push LEAF(r4k_wait)
.set noreorder /* Keep the ISA bit clear for calculations on local labels here. */
/* start of rollback region */ 0: .fill 0
LONG_L t0, TI_FLAGS($28) /* Start of idle interrupt region. */
nop local_irq_enable
andi t0, _TIF_NEED_RESCHED /*
bnez t0, 1f * If an interrupt lands here, before going idle on the next
nop * instruction, we must *NOT* go idle since the interrupt could
nop * have set TIF_NEED_RESCHED or caused a timer to need resched.
nop * Fall through -- see rollback_handler below -- and have the
#ifdef CONFIG_CPU_MICROMIPS * idle loop take care of things.
nop */
nop 1: .fill 0
nop /* The R2 EI/EHB sequence takes 8 bytes, otherwise pad up. */
nop .if 1b - 0b > 32
#endif .error "overlong idle interrupt region"
.elseif 1b - 0b > 8
.align 4
.endif
2: .fill 0
.equ r4k_wait_idle_size, 2b - 0b
/* End of idle interrupt region; size has to be a power of 2. */
.set MIPS_ISA_ARCH_LEVEL_RAW .set MIPS_ISA_ARCH_LEVEL_RAW
r4k_wait_insn:
wait wait
/* end of rollback region (the region size must be power of two) */ r4k_wait_exit:
1: .set mips0
local_irq_disable
jr ra jr ra
nop END(r4k_wait)
.set pop .previous
END(__r4k_wait)
.macro BUILD_ROLLBACK_PROLOGUE handler .macro BUILD_ROLLBACK_PROLOGUE handler
FEXPORT(rollback_\handler) FEXPORT(rollback_\handler)
.set push .set push
.set noat .set noat
MFC0 k0, CP0_EPC MFC0 k0, CP0_EPC
PTR_LA k1, __r4k_wait /* Subtract/add 2 to let the ISA bit propagate through the mask. */
ori k0, 0x1f /* 32 byte rollback region */ PTR_LA k1, r4k_wait_insn - 2
xori k0, 0x1f ori k0, r4k_wait_idle_size - 2
.set noreorder
bne k0, k1, \handler bne k0, k1, \handler
PTR_ADDIU k0, r4k_wait_exit - r4k_wait_insn + 2
.set reorder
MTC0 k0, CP0_EPC MTC0 k0, CP0_EPC
.set pop .set pop
.endm .endm

7
arch/mips/kernel/idle.c
View File

@ -35,13 +35,6 @@ static void __cpuidle r3081_wait(void)
write_c0_conf(cfg | R30XX_CONF_HALT); write_c0_conf(cfg | R30XX_CONF_HALT);
} }
void __cpuidle r4k_wait(void)
{
raw_local_irq_enable();
__r4k_wait();
raw_local_irq_disable();
}
/* /*
* This variant is preferable as it allows testing need_resched and going to * This variant is preferable as it allows testing need_resched and going to
* sleep depending on the outcome atomically. Unfortunately the "It is * sleep depending on the outcome atomically. Unfortunately the "It is