| Message ID | 20250228100509.91121-2-marco.crivellari@suse.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | MIPS: Fix idle VS timer enqueue | expand |
Le Fri, Feb 28, 2025 at 11:05:09AM +0100, Marco Crivellari a écrit : > 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. > > Signed-off-by: Marco Crivellari <marco.crivellari@suse.com> Acked-by: Frederic Weisbecker <frederic@kernel.org>
diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S index a572ce36a24f..474738d9124e 100644 --- a/arch/mips/kernel/genex.S +++ b/arch/mips/kernel/genex.S @@ -104,27 +104,30 @@ handle_vcei: __FINIT - .align 5 /* 32 byte rollback region */ + .align 5 LEAF(__r4k_wait) .set push .set noreorder - /* start of rollback region */ - LONG_L t0, TI_FLAGS($28) - nop - andi t0, _TIF_NEED_RESCHED - bnez t0, 1f - nop - nop - nop -#ifdef CONFIG_CPU_MICROMIPS - nop - nop - nop - nop -#endif + /* start of idle interrupt region */ + MFC0 t0, CP0_STATUS + /* Enable Interrput */ + ori t0, 0x1f + xori t0, 0x1e + MTC0 t0, CP0_STATUS + _ssnop + _ssnop + _ssnop + _ehb .set MIPS_ISA_ARCH_LEVEL_RAW + /* + * If an interrupt lands here, between enabling interrupts above and + * going idle on the next instruction, we must *NOT* go idle since the + * interrupt could have set TIF_NEED_RESCHED or caused a timer to need + * resched. Fall through -- see rollback_handler below -- and have + * the idle loop take care of things. + */ wait - /* end of rollback region (the region size must be power of two) */ + /* end of idle interrupt region */ 1: jr ra nop @@ -136,9 +139,10 @@ LEAF(__r4k_wait) .set push .set noat MFC0 k0, CP0_EPC - PTR_LA k1, __r4k_wait - ori k0, 0x1f /* 32 byte rollback region */ - xori k0, 0x1f + PTR_LA k1, 1b + /* 36 byte idle interrupt region */ + ori k0, 0x1f + PTR_ADDIU k0, 5 bne k0, k1, \handler MTC0 k0, CP0_EPC .set pop diff --git a/arch/mips/kernel/idle.c b/arch/mips/kernel/idle.c index 5abc8b7340f8..1f74c0589f7e 100644 --- a/arch/mips/kernel/idle.c +++ b/arch/mips/kernel/idle.c @@ -37,7 +37,6 @@ static void __cpuidle r3081_wait(void) void __cpuidle r4k_wait(void) { - raw_local_irq_enable(); __r4k_wait(); raw_local_irq_disable(); }
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. Signed-off-by: Marco Crivellari <marco.crivellari@suse.com> --- arch/mips/kernel/genex.S | 42 ++++++++++++++++++++++------------------ arch/mips/kernel/idle.c | 1 - 2 files changed, 23 insertions(+), 20 deletions(-)