Re: [PATCH v6 05/12] powerpc: reverse the soft_enable logic

On Mon,  9 Jan 2017 19:06:11 +0530
Madhavan Srinivasan [off-list ref] wrote:

"paca->soft_enabled" is used as a flag to mask some of interrupts.
Currently supported flags values and their details:

soft_enabled    MSR[EE]

0               0       Disabled (PMI and HMI not masked)
1               1       Enabled

"paca->soft_enabled" is initialized to 1 to make the interripts as
enabled. arch_local_irq_disable() will toggle the value when interrupts
needs to disbled. At this point, the interrupts are not actually disabled,
instead, interrupt vector has code to check for the flag and mask it when it occurs.
By "mask it", it update interrupt paca->irq_happened and return.
arch_local_irq_restore() is called to re-enable interrupts, which checks and
replays interrupts if any occured.

Now, as mentioned, current logic doesnot mask "performance monitoring interrupts"
and PMIs are implemented as NMI. But this patchset depends on local_irq_*
for a successful local_* update. Meaning, mask all possible interrupts during
local_* update and replay them after the update.

So the idea here is to reserve the "paca->soft_enabled" logic. New values and
details:

soft_enabled    MSR[EE]

1               0       Disabled  (PMI and HMI not masked)
0               1       Enabled

Reason for the this change is to create foundation for a third mask value "0x2"
for "soft_enabled" to add support to mask PMIs. When ->soft_enabled is
set to a value "3", PMI interrupts are mask and when set to a value
of "1", PMI are not mask. With this patch also extends soft_enabled
interrupt disable mask.

Signed-off-by: Madhavan Srinivasan <redacted>

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>