Patchwork [RFC,09/11] kvm: simplify processor compat check

login
register
mail settings
Submitter Aneesh Kumar K.V
Date Sept. 27, 2013, 10:03 a.m.
Message ID <1380276233-17095-10-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/278519/
State Not Applicable
Headers show

Comments

Aneesh Kumar K.V - Sept. 27, 2013, 10:03 a.m.
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/arm/kvm/arm.c                 |  4 ++--
 arch/ia64/kvm/kvm-ia64.c           |  4 ++--
 arch/mips/kvm/kvm_mips.c           |  6 ++----
 arch/powerpc/include/asm/kvm_ppc.h |  2 +-
 arch/powerpc/kvm/44x.c             |  2 +-
 arch/powerpc/kvm/book3s.c          | 15 ++++++++++++---
 arch/powerpc/kvm/book3s_hv.c       |  9 ++++++---
 arch/powerpc/kvm/book3s_pr.c       |  5 +++--
 arch/powerpc/kvm/e500.c            |  2 +-
 arch/powerpc/kvm/e500mc.c          |  2 +-
 arch/powerpc/kvm/powerpc.c         |  5 -----
 arch/s390/kvm/kvm-s390.c           |  3 ++-
 arch/x86/kvm/x86.c                 | 13 +++++++++++--
 include/linux/kvm_host.h           |  2 +-
 virt/kvm/kvm_main.c                | 14 +++++---------
 15 files changed, 50 insertions(+), 38 deletions(-)
Alexander Graf - Sept. 27, 2013, 12:31 p.m.
On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:

> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

Missing patch description.

> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

I fail to see how this really simplifies things, but at the end of the day it's Gleb's and Paolo's call.

Which brings me to the next issue: You forgot to CC kvm@vger on your patch set. Gleb and Paolo don't read kvm-ppc@vger. And they shouldn't have to. Every kvm patch that you want review on or that should get applied needs to be sent to kvm@vger. If you want to tag it as PPC specific patch, do so by CC'ing kvm-ppc@vger.


Alex

> ---
> arch/arm/kvm/arm.c                 |  4 ++--
> arch/ia64/kvm/kvm-ia64.c           |  4 ++--
> arch/mips/kvm/kvm_mips.c           |  6 ++----
> arch/powerpc/include/asm/kvm_ppc.h |  2 +-
> arch/powerpc/kvm/44x.c             |  2 +-
> arch/powerpc/kvm/book3s.c          | 15 ++++++++++++---
> arch/powerpc/kvm/book3s_hv.c       |  9 ++++++---
> arch/powerpc/kvm/book3s_pr.c       |  5 +++--
> arch/powerpc/kvm/e500.c            |  2 +-
> arch/powerpc/kvm/e500mc.c          |  2 +-
> arch/powerpc/kvm/powerpc.c         |  5 -----
> arch/s390/kvm/kvm-s390.c           |  3 ++-
> arch/x86/kvm/x86.c                 | 13 +++++++++++--
> include/linux/kvm_host.h           |  2 +-
> virt/kvm/kvm_main.c                | 14 +++++---------
> 15 files changed, 50 insertions(+), 38 deletions(-)
> 
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 9c697db..cccb121 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -109,9 +109,9 @@ void kvm_arch_hardware_unsetup(void)
> {
> }
> 
> -void kvm_arch_check_processor_compat(void *rtn)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> -	*(int *)rtn = 0;
> +	return 0;
> }
> 
> void kvm_arch_sync_events(struct kvm *kvm)
> diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
> index bdfd878..065942c 100644
> --- a/arch/ia64/kvm/kvm-ia64.c
> +++ b/arch/ia64/kvm/kvm-ia64.c
> @@ -185,9 +185,9 @@ void kvm_arch_hardware_disable(void *garbage)
> 	ia64_ptr_entry(0x3, slot);
> }
> 
> -void kvm_arch_check_processor_compat(void *rtn)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> -	*(int *)rtn = 0;
> +	return 0;
> }
> 
> int kvm_dev_ioctl_check_extension(long ext)
> diff --git a/arch/mips/kvm/kvm_mips.c b/arch/mips/kvm/kvm_mips.c
> index a7b0445..4512739 100644
> --- a/arch/mips/kvm/kvm_mips.c
> +++ b/arch/mips/kvm/kvm_mips.c
> @@ -97,11 +97,9 @@ void kvm_arch_hardware_unsetup(void)
> {
> }
> 
> -void kvm_arch_check_processor_compat(void *rtn)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> -	int *r = (int *)rtn;
> -	*r = 0;
> -	return;
> +	return 0;
> }
> 
> static void kvm_mips_init_tlbs(struct kvm *kvm)
> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index 58e732f..592501b 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -204,7 +204,7 @@ struct kvmppc_ops {
> 			      unsigned long npages);
> 	int (*init_vm)(struct kvm *kvm);
> 	void (*destroy_vm)(struct kvm *kvm);
> -	int (*check_processor_compat)(void);
> +	void (*check_processor_compat)(void *r);
> 	int (*get_smmu_info)(struct kvm *kvm, struct kvm_ppc_smmu_info *info);
> 	int (*emulate_op)(struct kvm_run *run, struct kvm_vcpu *vcpu,
> 			  unsigned int inst, int *advance);
> diff --git a/arch/powerpc/kvm/44x.c b/arch/powerpc/kvm/44x.c
> index 2f5c6b6..a1f4e60 100644
> --- a/arch/powerpc/kvm/44x.c
> +++ b/arch/powerpc/kvm/44x.c
> @@ -43,7 +43,7 @@ void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
> 	kvmppc_booke_vcpu_put(vcpu);
> }
> 
> -int kvmppc_core_check_processor_compat(void)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> 	int r;
> 
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index ca617e1..485a6ff 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -827,9 +827,18 @@ void kvmppc_core_destroy_vm(struct kvm *kvm)
> #endif
> }
> 
> -int kvmppc_core_check_processor_compat(void)
> -{
> -	return kvmppc_ops->check_processor_compat();
> +int kvm_arch_check_processor_compat(void *opaque)
> +{
> +	int r,cpu;
> +	struct kvmppc_ops *kvm_ops = (struct kvmppc_ops *)opaque;
> +	for_each_online_cpu(cpu) {
> +		smp_call_function_single(cpu,
> +					 kvm_ops->check_processor_compat,
> +					 &r, 1);
> +		if (r < 0)
> +			break;
> +	}
> +	return r;
> }
> 
> EXPORT_SYMBOL_GPL(kvm_get_dirty_log);
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index ff57be8..4322db4 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1980,11 +1980,14 @@ static int kvmppc_core_emulate_mfspr_hv(struct kvm_vcpu *vcpu, int sprn,
> 	return EMULATE_FAIL;
> }
> 
> -static int kvmppc_core_check_processor_compat_hv(void)
> +
> +static void kvmppc_core_check_processor_compat_hv(void *r)
> {
> 	if (!cpu_has_feature(CPU_FTR_HVMODE))
> -		return -EIO;
> -	return 0;
> +		*(int *)r = -EIO;
> +	else
> +		*(int *)r = 0;
> +	return;
> }
> 
> static long kvm_arch_vm_ioctl_hv(struct file *filp,
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index df48d89..127b961 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -1490,10 +1490,11 @@ static void kvmppc_core_destroy_vm_pr(struct kvm *kvm)
> 	enable_relon_interrupts(kvm);
> }
> 
> -static int kvmppc_core_check_processor_compat_pr(void)
> +static void kvmppc_core_check_processor_compat_pr(void *r)
> {
> 	/* we are always compatible */
> -	return 0;
> +	*(int *)r = 0;
> +	return;
> }
> 
> static long kvm_arch_vm_ioctl_pr(struct file *filp,
> diff --git a/arch/powerpc/kvm/e500.c b/arch/powerpc/kvm/e500.c
> index ce6b73c..0681cb1 100644
> --- a/arch/powerpc/kvm/e500.c
> +++ b/arch/powerpc/kvm/e500.c
> @@ -323,7 +323,7 @@ void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
> 	kvmppc_booke_vcpu_put(vcpu);
> }
> 
> -int kvmppc_core_check_processor_compat(void)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> 	int r;
> 
> diff --git a/arch/powerpc/kvm/e500mc.c b/arch/powerpc/kvm/e500mc.c
> index 19c8379..48b3ba5 100644
> --- a/arch/powerpc/kvm/e500mc.c
> +++ b/arch/powerpc/kvm/e500mc.c
> @@ -169,7 +169,7 @@ void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
> 	kvmppc_booke_vcpu_put(vcpu);
> }
> 
> -int kvmppc_core_check_processor_compat(void)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> 	int r;
> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 3019edc..1404f4d 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -264,11 +264,6 @@ void kvm_arch_hardware_unsetup(void)
> {
> }
> 
> -void kvm_arch_check_processor_compat(void *rtn)
> -{
> -	*(int *)rtn = kvmppc_core_check_processor_compat();
> -}
> -
> int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> {
> 	if (type)
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 776dafe..01d4000 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -119,8 +119,9 @@ void kvm_arch_hardware_unsetup(void)
> 	gmap_unregister_ipte_notifier(&gmap_notifier);
> }
> 
> -void kvm_arch_check_processor_compat(void *rtn)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> +	return 0;
> }
> 
> int kvm_arch_init(void *opaque)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e5ca72a..53c8308 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6873,9 +6873,18 @@ void kvm_arch_hardware_unsetup(void)
> 	kvm_x86_ops->hardware_unsetup();
> }
> 
> -void kvm_arch_check_processor_compat(void *rtn)
> +int kvm_arch_check_processor_compat(void *opaque)
> {
> -	kvm_x86_ops->check_processor_compatibility(rtn);
> +	int r,cpu;
> +
> +	for_each_online_cpu(cpu) {
> +		smp_call_function_single(cpu,
> +			 kvm_x86_ops->check_processor_compatibility,
> +			 &r, 1);
> +		if (r < 0)
> +			break;
> +	}
> +	return r;
> }
> 
> bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index ca645a0..459b359 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -649,7 +649,7 @@ int kvm_arch_hardware_enable(void *garbage);
> void kvm_arch_hardware_disable(void *garbage);
> int kvm_arch_hardware_setup(void);
> void kvm_arch_hardware_unsetup(void);
> -void kvm_arch_check_processor_compat(void *rtn);
> +int kvm_arch_check_processor_compat(void *opaque);
> int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 66df1d2..0594b22 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3166,10 +3166,9 @@ static void kvm_sched_out(struct preempt_notifier *pn,
> }
> 
> int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
> -		  struct module *module)
> +	     struct module *module)
> {
> 	int r;
> -	int cpu;
> 
> 	r = kvm_arch_init(opaque);
> 	if (r)
> @@ -3195,13 +3194,10 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
> 	if (r < 0)
> 		goto out_free_0a;
> 
> -	for_each_online_cpu(cpu) {
> -		smp_call_function_single(cpu,
> -				kvm_arch_check_processor_compat,
> -				&r, 1);
> -		if (r < 0)
> -			goto out_free_1;
> -	}
> +
> +	r = kvm_arch_check_processor_compat(opaque);
> +	if (r < 0)
> +		goto out_free_1;
> 
> 	r = register_cpu_notifier(&kvm_cpu_notifier);
> 	if (r)
> -- 
> 1.8.1.2
>
Aneesh Kumar K.V - Sept. 27, 2013, 1:13 p.m.
Alexander Graf <agraf@suse.de> writes:

> On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:
>
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>
> Missing patch description.
>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>
> I fail to see how this really simplifies things, but at the end of the
> day it's Gleb's and Paolo's call.

will do. It avoid calling 

	for_each_online_cpu(cpu) {
		smp_call_function_single() 

on multiple architecture.

We also want to make the smp call function a callback of opaque. Hence
this should be made arch specific. 

int kvm_arch_check_processor_compat(void *opaque)
{
	int r,cpu;
	struct kvmppc_ops *kvm_ops = (struct kvmppc_ops *)opaque;
	for_each_online_cpu(cpu) {
		smp_call_function_single(cpu,
					 kvm_ops->check_processor_compat,
					 &r, 1);
		if (r < 0)
			break;
	}
	return r;
}

against

-	for_each_online_cpu(cpu) {
-		smp_call_function_single(cpu,
-				kvm_arch_check_processor_compat,
-				&r, 1);
-		if (r < 0)
-			goto out_free_1;
-	}
+
+	r = kvm_arch_check_processor_compat(opaque);
+	if (r < 0)
+		goto out_free_1;



>
> Which brings me to the next issue: You forgot to CC kvm@vger on your
> patch set. Gleb and Paolo don't read kvm-ppc@vger. And they shouldn't
> have to. Every kvm patch that you want review on or that should get
> applied needs to be sent to kvm@vger. If you want to tag it as PPC
> specific patch, do so by CC'ing kvm-ppc@vger.

Will do in the next update

-aneesh
Paolo Bonzini - Sept. 27, 2013, 3:14 p.m.
Il 27/09/2013 15:13, Aneesh Kumar K.V ha scritto:
> Alexander Graf <agraf@suse.de> writes:
> 
>> On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:
>>
>>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>>
>> Missing patch description.
>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>>
>> I fail to see how this really simplifies things, but at the end of the
>> day it's Gleb's and Paolo's call.
> 
> will do. It avoid calling 
> 
> 	for_each_online_cpu(cpu) {
> 		smp_call_function_single() 
> 
> on multiple architecture.

I agree with Alex.

The current code is not specially awesome; having
kvm_arch_check_processor_compat take an int* disguised as a void* is a
bit ugly indeed.

However, the API makes sense and tells you that it is being passed as a
callback (to smp_call_function_single in this case).

You are making the API more complicated to use on the arch layer
(because arch maintainers now have to think "do I need to check this on
all online CPUs?") and making the "leaf" POWER code less legible because
it still has the weird void()(void *) calling convention.

If anything, you could change kvm_arch_check_processor_compat to return
an int and accept no argument, and introduce a wrapper that kvm_init
passes to smp_call_function_single.

Paolo

> We also want to make the smp call function a callback of opaque. Hence
> this should be made arch specific. 
> 
> int kvm_arch_check_processor_compat(void *opaque)
> {
> 	int r,cpu;
> 	struct kvmppc_ops *kvm_ops = (struct kvmppc_ops *)opaque;
> 	for_each_online_cpu(cpu) {
> 		smp_call_function_single(cpu,
> 					 kvm_ops->check_processor_compat,
> 					 &r, 1);
> 		if (r < 0)
> 			break;
> 	}
> 	return r;
> }
> 
> against
> 
> -	for_each_online_cpu(cpu) {
> -		smp_call_function_single(cpu,
> -				kvm_arch_check_processor_compat,
> -				&r, 1);
> -		if (r < 0)
> -			goto out_free_1;
> -	}
> +
> +	r = kvm_arch_check_processor_compat(opaque);
> +	if (r < 0)
> +		goto out_free_1;
> 
> 
> 
>>
>> Which brings me to the next issue: You forgot to CC kvm@vger on your
>> patch set. Gleb and Paolo don't read kvm-ppc@vger. And they shouldn't
>> have to. Every kvm patch that you want review on or that should get
>> applied needs to be sent to kvm@vger. If you want to tag it as PPC
>> specific patch, do so by CC'ing kvm-ppc@vger.
> 
> Will do in the next update
> 
> -aneesh
>
Aneesh Kumar K.V - Sept. 28, 2013, 3:36 p.m.
Paolo Bonzini <pbonzini@redhat.com> writes:

> Il 27/09/2013 15:13, Aneesh Kumar K.V ha scritto:
>> Alexander Graf <agraf@suse.de> writes:
>> 
>>> On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:
>>>
>>>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>>>
>>> Missing patch description.
>>>
>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>>>
>>> I fail to see how this really simplifies things, but at the end of the
>>> day it's Gleb's and Paolo's call.
>> 
>> will do. It avoid calling 
>> 
>> 	for_each_online_cpu(cpu) {
>> 		smp_call_function_single() 
>> 
>> on multiple architecture.
>
> I agree with Alex.
>
> The current code is not specially awesome; having
> kvm_arch_check_processor_compat take an int* disguised as a void* is a
> bit ugly indeed.
>
> However, the API makes sense and tells you that it is being passed as a
> callback (to smp_call_function_single in this case).

But whether to check on all cpus or not is arch dependent right?.
IIUC only x86 and ppc64 need to do that. Also on ppc64 it really
depends on whether HV or PR. We need to check on all cpus only if it is
HV. 

>
> You are making the API more complicated to use on the arch layer
> (because arch maintainers now have to think "do I need to check this on
> all online CPUs?") and making the "leaf" POWER code less legible because
> it still has the weird void()(void *) calling convention.
>

IIUC what we wanted to check is to find out whether kvm can run on this
system. That is really an arch specific check. So for core kvm the call
should be a simple 

if (kvm_arch_check_process_compat() < 0)
        error;

Now how each arch figure out whether kvm can run on this system should
be arch specific. For x86 we do need to check all the cpus. On ppc64 for
HV we need to. For other archs we always allow kvm. 


> If anything, you could change kvm_arch_check_processor_compat to return
> an int and accept no argument, and introduce a wrapper that kvm_init
> passes to smp_call_function_single.

What i am suggesting in the patch is to avoid calling
smp_call_function_single from kvm_init and let arch decide whether to
check on all cpus or not.

-aneesh
Gleb Natapov - Sept. 29, 2013, 8:58 a.m.
On Sat, Sep 28, 2013 at 09:06:47PM +0530, Aneesh Kumar K.V wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
> > Il 27/09/2013 15:13, Aneesh Kumar K.V ha scritto:
> >> Alexander Graf <agraf@suse.de> writes:
> >> 
> >>> On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:
> >>>
> >>>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> >>>
> >>> Missing patch description.
> >>>
> >>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> >>>
> >>> I fail to see how this really simplifies things, but at the end of the
> >>> day it's Gleb's and Paolo's call.
> >> 
> >> will do. It avoid calling 
> >> 
> >> 	for_each_online_cpu(cpu) {
> >> 		smp_call_function_single() 
> >> 
> >> on multiple architecture.
> >
> > I agree with Alex.
> >
> > The current code is not specially awesome; having
> > kvm_arch_check_processor_compat take an int* disguised as a void* is a
> > bit ugly indeed.
> >
> > However, the API makes sense and tells you that it is being passed as a
> > callback (to smp_call_function_single in this case).
> 
> But whether to check on all cpus or not is arch dependent right?.
> IIUC only x86 and ppc64 need to do that. Also on ppc64 it really
> depends on whether HV or PR. We need to check on all cpus only if it is
> HV. 
> 
> >
> > You are making the API more complicated to use on the arch layer
> > (because arch maintainers now have to think "do I need to check this on
> > all online CPUs?") and making the "leaf" POWER code less legible because
> > it still has the weird void()(void *) calling convention.
> >
> 
> IIUC what we wanted to check is to find out whether kvm can run on this
> system. That is really an arch specific check. So for core kvm the call
> should be a simple 
> 
> if (kvm_arch_check_process_compat() < 0)
>         error;
We have that already, just return error from kvm_arch_hardware_setup. This
is specific processor compatibility check and you are arguing that the
processor check should be part of kvm_arch_hardware_setup().

> 
> Now how each arch figure out whether kvm can run on this system should
> be arch specific. For x86 we do need to check all the cpus. On ppc64 for
> HV we need to. For other archs we always allow kvm. 
> 
This is really a sanity check. Theoretically on x86 we also should
not need to check all cpus since SMP configuration with different cpu
models is not supported by the architecture (AFAIK), but bugs happen
(BIOS bugs may cause difference in capabilities for instance). So some
arches opted out from this sanity check for now and this is their choice,
but the code makes it explicit what are we checking here.

> 
> > If anything, you could change kvm_arch_check_processor_compat to return
> > an int and accept no argument, and introduce a wrapper that kvm_init
> > passes to smp_call_function_single.
> 
> What i am suggesting in the patch is to avoid calling
> smp_call_function_single from kvm_init and let arch decide whether to
> check on all cpus or not.
> 
> -aneesh

--
			Gleb.
Aneesh Kumar K.V - Sept. 29, 2013, 3:05 p.m.
Gleb Natapov <gleb@redhat.com> writes:

> On Sat, Sep 28, 2013 at 09:06:47PM +0530, Aneesh Kumar K.V wrote:
>> Paolo Bonzini <pbonzini@redhat.com> writes:
>> 
>> > Il 27/09/2013 15:13, Aneesh Kumar K.V ha scritto:
>> >> Alexander Graf <agraf@suse.de> writes:
>> >> 
>> >>> On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:
>> >>>
>> >>>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>> >>>
>> >>> Missing patch description.
>> >>>
>> >>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> >>>
>> >>> I fail to see how this really simplifies things, but at the end of the
>> >>> day it's Gleb's and Paolo's call.
>> >> 
>> >> will do. It avoid calling 
>> >> 
>> >> 	for_each_online_cpu(cpu) {
>> >> 		smp_call_function_single() 
>> >> 
>> >> on multiple architecture.
>> >
>> > I agree with Alex.
>> >
>> > The current code is not specially awesome; having
>> > kvm_arch_check_processor_compat take an int* disguised as a void* is a
>> > bit ugly indeed.
>> >
>> > However, the API makes sense and tells you that it is being passed as a
>> > callback (to smp_call_function_single in this case).
>> 
>> But whether to check on all cpus or not is arch dependent right?.
>> IIUC only x86 and ppc64 need to do that. Also on ppc64 it really
>> depends on whether HV or PR. We need to check on all cpus only if it is
>> HV. 
>> 
>> >
>> > You are making the API more complicated to use on the arch layer
>> > (because arch maintainers now have to think "do I need to check this on
>> > all online CPUs?") and making the "leaf" POWER code less legible because
>> > it still has the weird void()(void *) calling convention.
>> >
>> 
>> IIUC what we wanted to check is to find out whether kvm can run on this
>> system. That is really an arch specific check. So for core kvm the call
>> should be a simple 
>> 
>> if (kvm_arch_check_process_compat() < 0)
>>         error;
> We have that already, just return error from kvm_arch_hardware_setup. This
> is specific processor compatibility check and you are arguing that the
> processor check should be part of kvm_arch_hardware_setup().


What about the success case ?. ie, on arch like arm we do

void kvm_arch_check_processor_compat(void *rtn)
{
	*(int *)rtn = 0;
}

for_each_online_cpu(cpu) {
	smp_call_function_single(cpu,
			kvm_arch_check_processor_compat,
			&r, 1);
	if (r < 0)
		goto out_free_1;
}

There is no need to do that for loop for arm. 

The only reason I wanted this patch in the series is to make
kvm_arch_check_processor_compat take additional argument opaque. 
I am dropping that requirement in the last patch. Considering
that we have objection to this one, I will drop this patch in
the next posting by rearranging the patches.

-aneesh
Gleb Natapov - Sept. 29, 2013, 3:11 p.m.
On Sun, Sep 29, 2013 at 08:35:16PM +0530, Aneesh Kumar K.V wrote:
> Gleb Natapov <gleb@redhat.com> writes:
> 
> > On Sat, Sep 28, 2013 at 09:06:47PM +0530, Aneesh Kumar K.V wrote:
> >> Paolo Bonzini <pbonzini@redhat.com> writes:
> >> 
> >> > Il 27/09/2013 15:13, Aneesh Kumar K.V ha scritto:
> >> >> Alexander Graf <agraf@suse.de> writes:
> >> >> 
> >> >>> On 27.09.2013, at 12:03, Aneesh Kumar K.V wrote:
> >> >>>
> >> >>>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> >> >>>
> >> >>> Missing patch description.
> >> >>>
> >> >>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> >> >>>
> >> >>> I fail to see how this really simplifies things, but at the end of the
> >> >>> day it's Gleb's and Paolo's call.
> >> >> 
> >> >> will do. It avoid calling 
> >> >> 
> >> >> 	for_each_online_cpu(cpu) {
> >> >> 		smp_call_function_single() 
> >> >> 
> >> >> on multiple architecture.
> >> >
> >> > I agree with Alex.
> >> >
> >> > The current code is not specially awesome; having
> >> > kvm_arch_check_processor_compat take an int* disguised as a void* is a
> >> > bit ugly indeed.
> >> >
> >> > However, the API makes sense and tells you that it is being passed as a
> >> > callback (to smp_call_function_single in this case).
> >> 
> >> But whether to check on all cpus or not is arch dependent right?.
> >> IIUC only x86 and ppc64 need to do that. Also on ppc64 it really
> >> depends on whether HV or PR. We need to check on all cpus only if it is
> >> HV. 
> >> 
> >> >
> >> > You are making the API more complicated to use on the arch layer
> >> > (because arch maintainers now have to think "do I need to check this on
> >> > all online CPUs?") and making the "leaf" POWER code less legible because
> >> > it still has the weird void()(void *) calling convention.
> >> >
> >> 
> >> IIUC what we wanted to check is to find out whether kvm can run on this
> >> system. That is really an arch specific check. So for core kvm the call
> >> should be a simple 
> >> 
> >> if (kvm_arch_check_process_compat() < 0)
> >>         error;
> > We have that already, just return error from kvm_arch_hardware_setup. This
> > is specific processor compatibility check and you are arguing that the
> > processor check should be part of kvm_arch_hardware_setup().
> 
> 
> What about the success case ?. ie, on arch like arm we do
> 
> void kvm_arch_check_processor_compat(void *rtn)
> {
> 	*(int *)rtn = 0;
> }
> 
> for_each_online_cpu(cpu) {
As I said they opted out from doing the check. They may reconsider after
first bad HW will be discovered.

> 	smp_call_function_single(cpu,
> 			kvm_arch_check_processor_compat,
> 			&r, 1);
> 	if (r < 0)
> 		goto out_free_1;
> }
> 
> There is no need to do that for loop for arm. 
It's done once during module initialisation. Why is this a big deal?

--
			Gleb.

Patch

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 9c697db..cccb121 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -109,9 +109,9 @@  void kvm_arch_hardware_unsetup(void)
 {
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void *opaque)
 {
-	*(int *)rtn = 0;
+	return 0;
 }
 
 void kvm_arch_sync_events(struct kvm *kvm)
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index bdfd878..065942c 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -185,9 +185,9 @@  void kvm_arch_hardware_disable(void *garbage)
 	ia64_ptr_entry(0x3, slot);
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void *opaque)
 {
-	*(int *)rtn = 0;
+	return 0;
 }
 
 int kvm_dev_ioctl_check_extension(long ext)
diff --git a/arch/mips/kvm/kvm_mips.c b/arch/mips/kvm/kvm_mips.c
index a7b0445..4512739 100644
--- a/arch/mips/kvm/kvm_mips.c
+++ b/arch/mips/kvm/kvm_mips.c
@@ -97,11 +97,9 @@  void kvm_arch_hardware_unsetup(void)
 {
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void *opaque)
 {
-	int *r = (int *)rtn;
-	*r = 0;
-	return;
+	return 0;
 }
 
 static void kvm_mips_init_tlbs(struct kvm *kvm)
diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
index 58e732f..592501b 100644
--- a/arch/powerpc/include/asm/kvm_ppc.h
+++ b/arch/powerpc/include/asm/kvm_ppc.h
@@ -204,7 +204,7 @@  struct kvmppc_ops {
 			      unsigned long npages);
 	int (*init_vm)(struct kvm *kvm);
 	void (*destroy_vm)(struct kvm *kvm);
-	int (*check_processor_compat)(void);
+	void (*check_processor_compat)(void *r);
 	int (*get_smmu_info)(struct kvm *kvm, struct kvm_ppc_smmu_info *info);
 	int (*emulate_op)(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			  unsigned int inst, int *advance);
diff --git a/arch/powerpc/kvm/44x.c b/arch/powerpc/kvm/44x.c
index 2f5c6b6..a1f4e60 100644
--- a/arch/powerpc/kvm/44x.c
+++ b/arch/powerpc/kvm/44x.c
@@ -43,7 +43,7 @@  void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
 	kvmppc_booke_vcpu_put(vcpu);
 }
 
-int kvmppc_core_check_processor_compat(void)
+int kvm_arch_check_processor_compat(void *opaque)
 {
 	int r;
 
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index ca617e1..485a6ff 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -827,9 +827,18 @@  void kvmppc_core_destroy_vm(struct kvm *kvm)
 #endif
 }
 
-int kvmppc_core_check_processor_compat(void)
-{
-	return kvmppc_ops->check_processor_compat();
+int kvm_arch_check_processor_compat(void *opaque)
+{
+	int r,cpu;
+	struct kvmppc_ops *kvm_ops = (struct kvmppc_ops *)opaque;
+	for_each_online_cpu(cpu) {
+		smp_call_function_single(cpu,
+					 kvm_ops->check_processor_compat,
+					 &r, 1);
+		if (r < 0)
+			break;
+	}
+	return r;
 }
 
 EXPORT_SYMBOL_GPL(kvm_get_dirty_log);
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index ff57be8..4322db4 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1980,11 +1980,14 @@  static int kvmppc_core_emulate_mfspr_hv(struct kvm_vcpu *vcpu, int sprn,
 	return EMULATE_FAIL;
 }
 
-static int kvmppc_core_check_processor_compat_hv(void)
+
+static void kvmppc_core_check_processor_compat_hv(void *r)
 {
 	if (!cpu_has_feature(CPU_FTR_HVMODE))
-		return -EIO;
-	return 0;
+		*(int *)r = -EIO;
+	else
+		*(int *)r = 0;
+	return;
 }
 
 static long kvm_arch_vm_ioctl_hv(struct file *filp,
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index df48d89..127b961 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -1490,10 +1490,11 @@  static void kvmppc_core_destroy_vm_pr(struct kvm *kvm)
 	enable_relon_interrupts(kvm);
 }
 
-static int kvmppc_core_check_processor_compat_pr(void)
+static void kvmppc_core_check_processor_compat_pr(void *r)
 {
 	/* we are always compatible */
-	return 0;
+	*(int *)r = 0;
+	return;
 }
 
 static long kvm_arch_vm_ioctl_pr(struct file *filp,
diff --git a/arch/powerpc/kvm/e500.c b/arch/powerpc/kvm/e500.c
index ce6b73c..0681cb1 100644
--- a/arch/powerpc/kvm/e500.c
+++ b/arch/powerpc/kvm/e500.c
@@ -323,7 +323,7 @@  void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
 	kvmppc_booke_vcpu_put(vcpu);
 }
 
-int kvmppc_core_check_processor_compat(void)
+int kvm_arch_check_processor_compat(void *opaque)
 {
 	int r;
 
diff --git a/arch/powerpc/kvm/e500mc.c b/arch/powerpc/kvm/e500mc.c
index 19c8379..48b3ba5 100644
--- a/arch/powerpc/kvm/e500mc.c
+++ b/arch/powerpc/kvm/e500mc.c
@@ -169,7 +169,7 @@  void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
 	kvmppc_booke_vcpu_put(vcpu);
 }
 
-int kvmppc_core_check_processor_compat(void)
+int kvm_arch_check_processor_compat(void *opaque)
 {
 	int r;
 
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 3019edc..1404f4d 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -264,11 +264,6 @@  void kvm_arch_hardware_unsetup(void)
 {
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
-{
-	*(int *)rtn = kvmppc_core_check_processor_compat();
-}
-
 int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 {
 	if (type)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 776dafe..01d4000 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -119,8 +119,9 @@  void kvm_arch_hardware_unsetup(void)
 	gmap_unregister_ipte_notifier(&gmap_notifier);
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void *opaque)
 {
+	return 0;
 }
 
 int kvm_arch_init(void *opaque)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e5ca72a..53c8308 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6873,9 +6873,18 @@  void kvm_arch_hardware_unsetup(void)
 	kvm_x86_ops->hardware_unsetup();
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void *opaque)
 {
-	kvm_x86_ops->check_processor_compatibility(rtn);
+	int r,cpu;
+
+	for_each_online_cpu(cpu) {
+		smp_call_function_single(cpu,
+			 kvm_x86_ops->check_processor_compatibility,
+			 &r, 1);
+		if (r < 0)
+			break;
+	}
+	return r;
 }
 
 bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ca645a0..459b359 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -649,7 +649,7 @@  int kvm_arch_hardware_enable(void *garbage);
 void kvm_arch_hardware_disable(void *garbage);
 int kvm_arch_hardware_setup(void);
 void kvm_arch_hardware_unsetup(void);
-void kvm_arch_check_processor_compat(void *rtn);
+int kvm_arch_check_processor_compat(void *opaque);
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
 int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 66df1d2..0594b22 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3166,10 +3166,9 @@  static void kvm_sched_out(struct preempt_notifier *pn,
 }
 
 int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
-		  struct module *module)
+	     struct module *module)
 {
 	int r;
-	int cpu;
 
 	r = kvm_arch_init(opaque);
 	if (r)
@@ -3195,13 +3194,10 @@  int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 	if (r < 0)
 		goto out_free_0a;
 
-	for_each_online_cpu(cpu) {
-		smp_call_function_single(cpu,
-				kvm_arch_check_processor_compat,
-				&r, 1);
-		if (r < 0)
-			goto out_free_1;
-	}
+
+	r = kvm_arch_check_processor_compat(opaque);
+	if (r < 0)
+		goto out_free_1;
 
 	r = register_cpu_notifier(&kvm_cpu_notifier);
 	if (r)