Re: [RFC PATCH 11/36] arm64: interrupts: introduce interrupt masking helpers for entry code

[Vladimir Murzin <vladimir.murzin@arm.com>]

On 7/10/26 10:44, Jinjie Ruan wrote:
>> +static __always_inline
>> +void arm64_update_exc_hwstate(arm64_exc_hwstate_t hwstate, bool update_pmr)
>> +{
>> +	if (system_uses_irq_prio_masking() &&
>> +	    update_pmr &&
>> +	    hwstate.pmr == GIC_PRIO_IRQOFF) {
>> +		/*
>> +		 * There has been concern that the write to daif
>> +		 * might be reordered before this write to PMR.
>> +		 * From the ARM ARM DDI 0487D.a, section D1.7.1
>> +		 * "Accessing PSTATE fields":
>> +		 *   Writes to the PSTATE fields have side-effects on
>> +		 *   various aspects of the PE operation. All of these
>> +		 *   side-effects are guaranteed:
>> +		 *     - Not to be visible to earlier instructions in
>> +		 *       the execution stream.
>> +		 *     - To be visible to later instructions in the
>> +		 *       execution stream
>> +		 *
>> +		 * Also, writes to PMR are self-synchronizing, so no
>> +		 * interrupts with a lower priority than PMR is signaled
>> +		 * to the PE after the write.
>> +		 *
>> +		 * So we don't need additional synchronization here.
>> +		 */
>> +		write_sysreg_s(hwstate.pmr, SYS_ICC_PMR_EL1);
>> +		pmr_sync();
>> +	}
>> +
>> +	write_sysreg(hwstate.daif, daif);
>> +
>> +	if (system_uses_irq_prio_masking() &&
>> +	    update_pmr &&
>> +	    hwstate.pmr == GIC_PRIO_IRQON) {
>> +		write_sysreg_s(hwstate.pmr, SYS_ICC_PMR_EL1);
>> +		pmr_sync();
> In the original local_daif_restore, pmr_sync is only required when
> interrupts are enabled. Is there any performance issue?
> 
> If all are using pmr_sync, why not merge it with the previous pmr
> operations?

IIUC, pmr_sync is not required for IRQOFF case. Please see my other
reply on this patch for the rationale behind structuring this function
this way.

Cheers
Vladimir