Re: [PATCH v3 08/10] x86/mtrr: let cache_aps_delayed_init replace mtrr_aps_delayed_init

From: Juergen Gross
Date: Wed Sep 28 2022 - 09:44:06 EST

On 28.09.22 13:22, Borislav Petkov wrote:
On Wed, Sep 28, 2022 at 01:14:11PM +0200, Juergen Gross wrote:
No, we don't.

Using basically your patch, but with

+ mtrr_online = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+ "x86/mtrr:online",
+ mtrr_ap_init, NULL);

moved to the end of mtrr_aps_init(), and:

+void mtrr_aps_thaw(void)
+{
+ cpuhp_remove_state_nocalls(mtrr_online);
+}

Yes, so you said. I'm not sure I like this toggling of notifier
registration like that.

Yeah, especially with having to remember the slot.

Would you feel better with adding a new enum member CPUHP_AP_CACHECTRL_ONLINE?

This would avoid a possible source of failure during resume in case no slot
for CPUHP_AP_ONLINE_DYN is found (quite improbable, but in theory possible).

Optimally, I'd like to be able to query the suspend code whether it is
in the process of resuming.

This here:


static int resume_target_kernel(bool platform_mode)
{

...

Enable_irqs:
system_state = SYSTEM_RUNNING;
local_irq_enable();
Enable_cpus:
pm_sleep_enable_secondary_cpus();


but being able to do:

pm_sleep_enable_secondary_cpus();
system_state = SYSTEM_RUNNING | SYSTEM_RUNNING_APS_UP;

which can't work, obviously. But something like that.


You wouldn't want to do that there, as there are multiple places where
pm_sleep_enable_secondary_cpus() is being called. Additionally not all
cases are coming in via pm_sleep_enable_secondary_cpus(), as there is
e.g. a call of suspend_enable_secondary_cpus() from kernel_kexec(),
which wants to have the same handling.

arch_thaw_secondary_cpus_begin() and arch_thaw_secondary_cpus_end() are
the functions to mark start and end of the special region where the
delayed MTRR setup should happen.


Juergen

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