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[Qemu-devel] [PATCH 8/8] spapr: Clean up handling of LPCR power-saving exit bits

David Gibson posted 8 patches 7 years, 5 months ago
[Qemu-devel] [PATCH 8/8] spapr: Clean up handling of LPCR power-saving exit bits
Posted by David Gibson 7 years, 5 months ago 
To prevent spurious wakeups on cpus that are supposed to be disabled, we
need to clear the LPCR bits which control certain wakeup events.
spapr_cpu_reset() has separate cases here for boot and non-boot (initially
inactive) cpus.  rtas_start_cpu() then turns the LPCR bits on when the
non-boot cpus are activated.

But explicit checks against first_cpu are not how we usually do things:
instead spapr_cpu_reset() generally sets things up for non-boot (inactive)
cpus, then spapr_machine_reset() and/or rtas_start_cpu() override as
necessary.

So, do that instead.  Because the LPCR activation is identical for boot
cpus and non-boot cpus just activated with rtas_start_cpu() we can put the
code common in spapr_cpu_set_entry_state().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/ppc/spapr_cpu_core.c | 22 +++++++---------------
 hw/ppc/spapr_rtas.c     |  2 +-
 2 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
index a52ddade5e..f3e9b879b2 100644
--- a/hw/ppc/spapr_cpu_core.c
+++ b/hw/ppc/spapr_cpu_core.c
@@ -54,28 +54,17 @@ static void spapr_cpu_reset(void *opaque)
      * Clearing VPM0 will also cause us to use RMOR in mmu-hash64.c for
      * real mode accesses, which thankfully defaults to 0 and isn't
      * accessible in guest mode.
+     *
+     * Disable Power-saving mode Exit Cause exceptions for the CPU, so
+     * we don't get spurious wakups before an RTAS start-cpu call.
      */
-    lpcr &= ~(LPCR_VPM0 | LPCR_VPM1 | LPCR_ISL | LPCR_KBV);
+    lpcr &= ~(LPCR_VPM0 | LPCR_VPM1 | LPCR_ISL | LPCR_KBV | pcc->lpcr_pm);
     lpcr |= LPCR_LPES0 | LPCR_LPES1;
 
     /* Set RMLS to the max (ie, 16G) */
     lpcr &= ~LPCR_RMLS;
     lpcr |= 1ull << LPCR_RMLS_SHIFT;
 
-    /* Only enable Power-saving mode Exit Cause exceptions on the boot
-     * CPU. The RTAS command start-cpu will enable them on secondaries.
-     */
-    if (cs == first_cpu) {
-        lpcr |= pcc->lpcr_pm;
-    }
-
-    /* Disable Power-saving mode Exit Cause exceptions for the CPU.
-     * This can cause issues when rebooting the guest if a secondary
-     * is awaken */
-    if (cs != first_cpu) {
-        lpcr &= ~pcc->lpcr_pm;
-    }
-
     ppc_store_lpcr(cpu, lpcr);
 
     /* Set a full AMOR so guest can use the AMR as it sees fit */
@@ -84,11 +73,14 @@ static void spapr_cpu_reset(void *opaque)
 
 void spapr_cpu_set_entry_state(PowerPCCPU *cpu, target_ulong nip, target_ulong r3)
 {
+    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
     CPUPPCState *env = &cpu->env;
 
     env->nip = nip;
     env->gpr[3] = r3;
     CPU(cpu)->halted = 0;
+    /* Enable Power-saving mode Exit Cause exceptions */
+    ppc_store_lpcr(cpu, env->spr[SPR_LPCR] | pcc->lpcr_pm);
 }
 
 static void spapr_cpu_destroy(PowerPCCPU *cpu)
diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 652233bdf1..7f9738daed 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -162,7 +162,7 @@ static void rtas_start_cpu(PowerPCCPU *callcpu, sPAPRMachineState *spapr,
     env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
 
     /* Enable Power-saving mode Exit Cause exceptions for the new CPU */
-    lpcr = env->spr[SPR_LPCR] | pcc->lpcr_pm;
+    lpcr = env->spr[SPR_LPCR];
     if (!pcc->interrupts_big_endian(callcpu)) {
         lpcr |= LPCR_ILE;
     }
-- 
2.17.0
Re: [Qemu-devel] [PATCH 8/8] spapr: Clean up handling of LPCR power-saving exit bits
Posted by Cédric Le Goater 7 years, 5 months ago 
On 05/03/2018 08:21 AM, David Gibson wrote:
> To prevent spurious wakeups on cpus that are supposed to be disabled, we
> need to clear the LPCR bits which control certain wakeup events.
> spapr_cpu_reset() has separate cases here for boot and non-boot (initially
> inactive) cpus.  rtas_start_cpu() then turns the LPCR bits on when the
> non-boot cpus are activated.
> 
> But explicit checks against first_cpu are not how we usually do things:
> instead spapr_cpu_reset() generally sets things up for non-boot (inactive)
> cpus, then spapr_machine_reset() and/or rtas_start_cpu() override as
> necessary.
> 
> So, do that instead.  Because the LPCR activation is identical for boot
> cpus and non-boot cpus just activated with rtas_start_cpu() we can put the
> code common in spapr_cpu_set_entry_state().

This is much nicer.

> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Reviewed-by: Cédric Le Goater <clg@kaod.org>

and for the patchset :

Tested-by: Cédric Le Goater <clg@kaod.org>

under KVM & TCG with cpu hotplug and unplug.


There is still a spapr_cpu_reset() call under spapr_cpu_init().
Is that on purpose ? 

Thanks,

C.

> ---
>  hw/ppc/spapr_cpu_core.c | 22 +++++++---------------
>  hw/ppc/spapr_rtas.c     |  2 +-
>  2 files changed, 8 insertions(+), 16 deletions(-)
> 
> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> index a52ddade5e..f3e9b879b2 100644
> --- a/hw/ppc/spapr_cpu_core.c
> +++ b/hw/ppc/spapr_cpu_core.c
> @@ -54,28 +54,17 @@ static void spapr_cpu_reset(void *opaque)
>       * Clearing VPM0 will also cause us to use RMOR in mmu-hash64.c for
>       * real mode accesses, which thankfully defaults to 0 and isn't
>       * accessible in guest mode.
> +     *
> +     * Disable Power-saving mode Exit Cause exceptions for the CPU, so
> +     * we don't get spurious wakups before an RTAS start-cpu call.
>       */
> -    lpcr &= ~(LPCR_VPM0 | LPCR_VPM1 | LPCR_ISL | LPCR_KBV);
> +    lpcr &= ~(LPCR_VPM0 | LPCR_VPM1 | LPCR_ISL | LPCR_KBV | pcc->lpcr_pm);
>      lpcr |= LPCR_LPES0 | LPCR_LPES1;
>  
>      /* Set RMLS to the max (ie, 16G) */
>      lpcr &= ~LPCR_RMLS;
>      lpcr |= 1ull << LPCR_RMLS_SHIFT;
>  
> -    /* Only enable Power-saving mode Exit Cause exceptions on the boot
> -     * CPU. The RTAS command start-cpu will enable them on secondaries.
> -     */
> -    if (cs == first_cpu) {
> -        lpcr |= pcc->lpcr_pm;
> -    }
> -
> -    /* Disable Power-saving mode Exit Cause exceptions for the CPU.
> -     * This can cause issues when rebooting the guest if a secondary
> -     * is awaken */
> -    if (cs != first_cpu) {
> -        lpcr &= ~pcc->lpcr_pm;
> -    }
> -
>      ppc_store_lpcr(cpu, lpcr);
>  
>      /* Set a full AMOR so guest can use the AMR as it sees fit */
> @@ -84,11 +73,14 @@ static void spapr_cpu_reset(void *opaque)
>  
>  void spapr_cpu_set_entry_state(PowerPCCPU *cpu, target_ulong nip, target_ulong r3)
>  {
> +    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
>      CPUPPCState *env = &cpu->env;
>  
>      env->nip = nip;
>      env->gpr[3] = r3;
>      CPU(cpu)->halted = 0;
> +    /* Enable Power-saving mode Exit Cause exceptions */
> +    ppc_store_lpcr(cpu, env->spr[SPR_LPCR] | pcc->lpcr_pm);
>  }
>  
>  static void spapr_cpu_destroy(PowerPCCPU *cpu)
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 652233bdf1..7f9738daed 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -162,7 +162,7 @@ static void rtas_start_cpu(PowerPCCPU *callcpu, sPAPRMachineState *spapr,
>      env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
>  
>      /* Enable Power-saving mode Exit Cause exceptions for the new CPU */
> -    lpcr = env->spr[SPR_LPCR] | pcc->lpcr_pm;
> +    lpcr = env->spr[SPR_LPCR];
>      if (!pcc->interrupts_big_endian(callcpu)) {
>          lpcr |= LPCR_ILE;
>      }
>
Re: [Qemu-devel] [PATCH 8/8] spapr: Clean up handling of LPCR power-saving exit bits
Posted by David Gibson 7 years, 5 months ago 
On Thu, May 03, 2018 at 09:47:18AM +0200, Cédric Le Goater wrote:
> On 05/03/2018 08:21 AM, David Gibson wrote:
> > To prevent spurious wakeups on cpus that are supposed to be disabled, we
> > need to clear the LPCR bits which control certain wakeup events.
> > spapr_cpu_reset() has separate cases here for boot and non-boot (initially
> > inactive) cpus.  rtas_start_cpu() then turns the LPCR bits on when the
> > non-boot cpus are activated.
> > 
> > But explicit checks against first_cpu are not how we usually do things:
> > instead spapr_cpu_reset() generally sets things up for non-boot (inactive)
> > cpus, then spapr_machine_reset() and/or rtas_start_cpu() override as
> > necessary.
> > 
> > So, do that instead.  Because the LPCR activation is identical for boot
> > cpus and non-boot cpus just activated with rtas_start_cpu() we can put the
> > code common in spapr_cpu_set_entry_state().
> 
> This is much nicer.
> 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> 
> Reviewed-by: Cédric Le Goater <clg@kaod.org>
> 
> and for the patchset :
> 
> Tested-by: Cédric Le Goater <clg@kaod.org>
> 
> under KVM & TCG with cpu hotplug and unplug.

Thanks.  I've folded the series into ppc-for-2.13.

> There is still a spapr_cpu_reset() call under spapr_cpu_init().
> Is that on purpose ?

Sort of.  I'd still like to remove it, but figuring out how to do so
safely is going to take a bit longer.  Well, probably quite a lot
longer, since I doubt I'll get it done before I go away.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
Re: [Qemu-devel] [PATCH 8/8] spapr: Clean up handling of LPCR power-saving exit bits
Posted by Cédric Le Goater 7 years, 5 months ago 
On 05/03/2018 01:59 PM, David Gibson wrote:
> On Thu, May 03, 2018 at 09:47:18AM +0200, Cédric Le Goater wrote:
>> On 05/03/2018 08:21 AM, David Gibson wrote:
>>> To prevent spurious wakeups on cpus that are supposed to be disabled, we
>>> need to clear the LPCR bits which control certain wakeup events.
>>> spapr_cpu_reset() has separate cases here for boot and non-boot (initially
>>> inactive) cpus.  rtas_start_cpu() then turns the LPCR bits on when the
>>> non-boot cpus are activated.
>>>
>>> But explicit checks against first_cpu are not how we usually do things:
>>> instead spapr_cpu_reset() generally sets things up for non-boot (inactive)
>>> cpus, then spapr_machine_reset() and/or rtas_start_cpu() override as
>>> necessary.
>>>
>>> So, do that instead.  Because the LPCR activation is identical for boot
>>> cpus and non-boot cpus just activated with rtas_start_cpu() we can put the
>>> code common in spapr_cpu_set_entry_state().
>>
>> This is much nicer.
>>
>>> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
>>
>> Reviewed-by: Cédric Le Goater <clg@kaod.org>
>>
>> and for the patchset :
>>
>> Tested-by: Cédric Le Goater <clg@kaod.org>
>>
>> under KVM & TCG with cpu hotplug and unplug.
> 
> Thanks.  I've folded the series into ppc-for-2.13.

We still need that patch for unplug to work :

	http://patchwork.ozlabs.org/patch/904229/

C.

>> There is still a spapr_cpu_reset() call under spapr_cpu_init().
>> Is that on purpose ?
> 
> Sort of.  I'd still like to remove it, but figuring out how to do so
> safely is going to take a bit longer.  Well, probably quite a lot
> longer, since I doubt I'll get it done before I go away.
>

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