Hi Huacai,
sorry, I completely forgot to check the comments!
On Thu, Feb 27, 2025 at 12:56 PM Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
>
> Hi, Marco,
>
> On Thu, Feb 27, 2025 at 7:41 PM Marco Crivellari
> <marco.crivellari@xxxxxxxx> wrote:
> >
> > 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@xxxxxxxx>
> > ---
> > arch/mips/kernel/genex.S | 40 ++++++++++++++++++++++------------------
> > arch/mips/kernel/idle.c | 1 -
> > 2 files changed, 22 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
> > index a572ce36a24f..7b66ab239049 100644
> > --- a/arch/mips/kernel/genex.S
> > +++ b/arch/mips/kernel/genex.S
> > @@ -104,25 +104,28 @@ 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) */
> Now you add a _ehb in this version, so "(the region size must be power
> of two)" should be removed.
>
> > 1:
> > @@ -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
> > + /* 32 byte idle interrupt region */
> And now the region is 36 bytes. :)
>
> Huacai
>
> > + 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();
> > }
> > --
> > 2.48.1
> >
--
Marco Crivellari
L3 Support Engineer, Technology & Product
marco.crivellari@xxxxxxxx
