[PATCH RFC] x86: avoid one cpu limit for kvm

[PATCH RFC] x86: avoid one cpu limit for kvm

[Jinyu Tang]

I run kernel by kvmtool but only one cpu can start in guset now, 
because kvm use virt-ioapic and kvmtool set noapic cmdline for 
x86 to disable ioapic route in kernel, and the latest cpu topo 
code below makes cpu limitted just to one.

For x86 kvm, noapic cmdline is reasonable, virt-ioapic don't
need to init hardware ioapic, so change it for x86 kvm guest to
avoid one num limit.

Signed-off-by: Jinyu Tang <tjytimi@163.com>
---
 arch/x86/kernel/cpu/topology.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index 621a151ccf7d..a73847b1a841 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -429,7 +429,9 @@ void __init topology_apply_cmdline_limits_early(void)
 	unsigned int possible = nr_cpu_ids;
 
 	/* 'maxcpus=0' 'nosmp' 'nolapic' 'disableapic' 'noapic' */
-	if (!setup_max_cpus || ioapic_is_disabled || apic_is_disabled)
+	if (!setup_max_cpus ||
+		(ioapic_is_disabled && (x86_hyper_type != X86_HYPER_KVM)) ||
+		apic_is_disabled)
 		possible = 1;
 
 	/* 'possible_cpus=N' */
@@ -443,8 +445,10 @@ void __init topology_apply_cmdline_limits_early(void)
 
 static __init bool restrict_to_up(void)
 {
-	if (!smp_found_config || ioapic_is_disabled)
+	if (!smp_found_config ||
+		(ioapic_is_disabled && (x86_hyper_type != X86_HYPER_KVM)))
 		return true;
+
 	/*
 	 * XEN PV is special as it does not advertise the local APIC
 	 * properly, but provides a fake topology for it so that the
-- 
2.43.0

Re: [PATCH RFC] x86: avoid one cpu limit for kvm

[Ingo Molnar]

* Jinyu Tang <tjytimi@163.com> wrote:

> I run kernel by kvmtool but only one cpu can start in guset now, 
> because kvm use virt-ioapic and kvmtool set noapic cmdline for 
> x86 to disable ioapic route in kernel, and the latest cpu topo 
> code below makes cpu limitted just to one.
> 
> For x86 kvm, noapic cmdline is reasonable, virt-ioapic don't
> need to init hardware ioapic, so change it for x86 kvm guest to
> avoid one num limit.
> 
> Signed-off-by: Jinyu Tang <tjytimi@163.com>
> ---
>  arch/x86/kernel/cpu/topology.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
> index 621a151ccf7d..a73847b1a841 100644
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -429,7 +429,9 @@ void __init topology_apply_cmdline_limits_early(void)
>  	unsigned int possible = nr_cpu_ids;
>  
>  	/* 'maxcpus=0' 'nosmp' 'nolapic' 'disableapic' 'noapic' */
> -	if (!setup_max_cpus || ioapic_is_disabled || apic_is_disabled)
> +	if (!setup_max_cpus ||
> +		(ioapic_is_disabled && (x86_hyper_type != X86_HYPER_KVM)) ||
> +		apic_is_disabled)
>  		possible = 1;
>  
>  	/* 'possible_cpus=N' */
> @@ -443,8 +445,10 @@ void __init topology_apply_cmdline_limits_early(void)
>  
>  static __init bool restrict_to_up(void)
>  {
> -	if (!smp_found_config || ioapic_is_disabled)
> +	if (!smp_found_config ||
> +		(ioapic_is_disabled && (x86_hyper_type != X86_HYPER_KVM)))
>  		return true;
> +
>  	/*
>  	 * XEN PV is special as it does not advertise the local APIC
>  	 * properly, but provides a fake topology for it so that the

Just to confirm that this bug got fixed, current kvmtool boots fine 
with multiple CPUs, correct?

Thanks,

	Ingo