BTW, some history coding here at kernel side:
-----------------------------------
commit ce5f68246bf2385d6174856708d0b746dc378f20
Author: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Date: Mon Sep 20 13:04:45 2010 -0700
x86, hotplug: In the MWAIT case of play_dead, CLFLUSH the cache line
When we're using MWAIT for play_dead, explicitly CLFLUSH the cache
line before executing MONITOR. This is a potential workaround for the
Xeon 7400 erratum AAI65 after having a spurious wakeup and returning
around the loop. "Potential" here because it is not certain that that
erratum could actually trigger; however, the CLFLUSH should be
harmless.
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Acked-by: Venkatesh Pallipadi <venki@xxxxxxxxxx>
Cc: Asit Mallick <asit.k.mallick@xxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
---------------------------------------
commit a68e5c94f7d3dd64fef34dd5d97e365cae4bb42a
Author: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Date: Fri Sep 17 17:06:46 2010 -0700
x86, hotplug: Move WBINVD back outside the play_dead loop
On processors with hyperthreading, when only one thread is offlined
the other thread can cause a spurious wakeup on the idled thread. We
do not want to re-WBINVD when that happens.
Ideally, we should simply skip WBINVD unless we're the last thread on
a particular core to shut down, but there might be similar issues
elsewhere in the system.
Thus, revert to previous behavior of only WBINVD outside the loop.
Partly as a result, remove the mb()'s around it: they are not
necessary since wbinvd() is a serializing instruction, but they were
intended to make sure the compiler didn't do any funny loop
optimizations.
Reported-by: Asit Mallick <asit.k.mallick@xxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Venkatesh Pallipadi <venki@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
--------------------------------------
commit ea53069231f9317062910d6e772cca4ce93de8c8
Author: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Date: Fri Sep 17 15:39:11 2010 -0700
x86, hotplug: Use mwait to offline a processor, fix the legacy case
The code in native_play_dead() has a number of problems:
1. We should use MWAIT when available, to put ourselves into a deeper
sleep state.
2. We use the existence of CLFLUSH to determine if WBINVD is safe, but
that is totally bogus -- WBINVD is 486+, whereas CLFLUSH is a much
later addition.
3. We should do WBINVD inside the loop, just in case of something like
setting an A bit on page tables. Pointed out by Arjan van de Ven.
This code is based in part of a previous patch by Venki Pallipadi, but
unlike that patch this one keeps all the detection code local instead
of pre-caching a bunch of information. We're shutting down the CPU;
there is absolutely no hurry.
This patch moves all the code to C and deletes the global
wbinvd_halt() which is broken anyway.
Originally-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Reviewed-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Venkatesh Pallipadi <venki@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---------------------------------------
Thanks,
Jinsong
Keir Fraser wrote:
> On 11/03/2011 14:34, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
>
>> Fix cache flush bug of cpu offline
>>
>> Current xen cpu offline logic flush cache too early, which
>> potentially break cache coherency. wbinvd should be the last ops
>> before cpu going into dead, otherwise cache may be dirty, i.e,
>> something like setting an A bit on page tables. Pointed out by Arjan
>> van de Ven.
>
> The position still seems a bit arbitrary. In the first hunk below,
> why is it safe to wbinvd() outside the for-loop and before reading
> cx->entry_method, but not before reading from processor_powers[]? It
> would be neater if we could put the wbinvd() in a wrapper function
> for calling *dead_idle.
>
> -- Keir
>
>> Signed-off-by: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
>>
>> diff -r 2dc3c1cc1bba xen/arch/x86/acpi/cpu_idle.c
>> --- a/xen/arch/x86/acpi/cpu_idle.c Mon Mar 07 05:31:46 2022 +0800
>> +++ b/xen/arch/x86/acpi/cpu_idle.c Thu Mar 10 23:40:51 2022 +0800
>> @@ -562,11 +562,14 @@ static void acpi_dead_idle(void)
>> if ( (cx = &power->states[power->count-1]) == NULL )
>> goto default_halt;
>>
>> + /*
>> + * cache must be flashed as the last ops before cpu going into
>> dead, + * otherwise, cpu may dead with dirty data breaking cache
>> coherency, + * leading to strange errors.
>> + */
>> + wbinvd();
>> for ( ; ; )
>> {
>> - if ( !power->flags.bm_check && cx->type == ACPI_STATE_C3 )
>> - ACPI_FLUSH_CPU_CACHE();
>> -
>> switch ( cx->entry_method )
>> {
>> case ACPI_CSTATE_EM_FFH:
>> @@ -584,6 +587,7 @@ static void acpi_dead_idle(void) }
>>
>> default_halt:
>> + wbinvd();
>> for ( ; ; )
>> halt();
>> }
>> diff -r 2dc3c1cc1bba xen/arch/x86/domain.c
>> --- a/xen/arch/x86/domain.c Mon Mar 07 05:31:46 2022 +0800
>> +++ b/xen/arch/x86/domain.c Thu Mar 10 23:40:51 2022 +0800
>> @@ -93,6 +93,12 @@ static void default_idle(void)
>>
>> static void default_dead_idle(void)
>> {
>> + /*
>> + * cache must be flashed as the last ops before cpu going into
>> dead, + * otherwise, cpu may dead with dirty data breaking cache
>> coherency, + * leading to strange errors.
>> + */
>> + wbinvd();
>> for ( ; ; )
>> halt();
>> }
>> @@ -100,7 +106,6 @@ static void play_dead(void)
>> static void play_dead(void)
>> {
>> local_irq_disable();
>> - wbinvd();
>>
>> /*
>> * NOTE: After cpu_exit_clear, per-cpu variables are no longer
>> accessible,
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