Re: [PATCH v2 2/3] powerpc/kvm/book3s_hv: Enable CPUs to run guest after waking up from fast-sleep

From: Benjamin Herrenschmidt
Date: Tue Oct 07 2014 - 01:11:45 EST


On Wed, 2014-10-01 at 13:15 +0530, Shreyas B. Prabhu wrote:
> When guests have to be launched, the secondary threads which are offline
> are woken up to run the guests. Today these threads wake up from nap
> and check if they have to run guests. Now that the offline secondary
> threads can go to fastsleep or going ahead a deeper idle state such as winkle,
> add this check in the wakeup from any of the deep idle states path as well.
>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Suggested-by: "Srivatsa S. Bhat" <srivatsa@xxxxxxx>
> Signed-off-by: Shreyas B. Prabhu <shreyas@xxxxxxxxxxxxxxxxxx>
> [ Changelog added by <preeti@xxxxxxxxxxxxxxxxxx> ]
> Signed-off-by: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/kernel/exceptions-64s.S | 35 ++++++++++++++++-------------------
> 1 file changed, 16 insertions(+), 19 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 050f79a..c64f3cc0 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -100,25 +100,8 @@ system_reset_pSeries:
> SET_SCRATCH0(r13)
> #ifdef CONFIG_PPC_P7_NAP
> BEGIN_FTR_SECTION
> - /* Running native on arch 2.06 or later, check if we are
> - * waking up from nap. We only handle no state loss and
> - * supervisor state loss. We do -not- handle hypervisor
> - * state loss at this time.
> - */
> - mfspr r13,SPRN_SRR1
> - rlwinm. r13,r13,47-31,30,31
> - beq 9f
>
> - /* waking up from powersave (nap) state */
> - cmpwi cr1,r13,2
> - /* Total loss of HV state is fatal, we could try to use the
> - * PIR to locate a PACA, then use an emergency stack etc...
> - * OPAL v3 based powernv platforms have new idle states
> - * which fall in this catagory.
> - */
> - bgt cr1,8f
> GET_PACA(r13)
> -
> #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> li r0,KVM_HWTHREAD_IN_KERNEL
> stb r0,HSTATE_HWTHREAD_STATE(r13)
> @@ -131,13 +114,27 @@ BEGIN_FTR_SECTION
> 1:
> #endif

So you moved the state loss check to after the KVM check ? Was this
reviewed by Paul ? Is that ok ? (Does this match what we have in
PowerKVM ?). Is it possible that we end up calling kvm_start_guest
after a HV state loss or do we know for sure that this won't happen
for a reason or another ? If that's the case, then that reason needs
to be clearly documented here in a comment.

> + /* Running native on arch 2.06 or later, check if we are
> + * waking up from nap. We only handle no state loss and
> + * supervisor state loss. We do -not- handle hypervisor
> + * state loss at this time.
> + */
> + mfspr r13,SPRN_SRR1
> + rlwinm. r13,r13,47-31,30,31
> + beq 9f
> +
> + /* waking up from powersave (nap) state */
> + cmpwi cr1,r13,2
> + GET_PACA(r13)
> +
> + bgt cr1,8f
> +
> beq cr1,2f
> b power7_wakeup_noloss
> 2: b power7_wakeup_loss
>
> /* Fast Sleep wakeup on PowerNV */
> -8: GET_PACA(r13)
> - b power7_wakeup_tb_loss
> +8: b power7_wakeup_tb_loss
>
> 9:
> END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)


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