linux-kernel - Re: [PATCH v2] kvm: x86: Limit the number of "kvm: disabled by bios" messages

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Date:   Fri, 28 Feb 2020 11:37:34 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Erwan Velu <erwanaliasr1@...il.com>
Cc:     Erwan Velu <e.velu@...teo.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)" 
        <kvm@...r.kernel.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kvm: x86: Limit the number of "kvm: disabled by bios"
 messages

On 27/02/20 19:00, Erwan Velu wrote:
> In older version of systemd(219), at boot time, udevadm is called with :
> 	/usr/bin/udevadm trigger --type=devices --action=add"
> 
> This program generates an echo "add" in /sys/devices/system/cpu/cpu<x>/uevent,
> leading to the "kvm: disabled by bios" message in case of your Bios disabled
> the virtualization extensions.
> 
> On a modern system running up to 256 CPU threads, this pollutes the Kernel logs.
> 
> This patch offers to ratelimit this message to avoid any userspace program triggering
> this uevent printing this message too often.
> 
> This patch is only a workaround but greatly reduce the pollution without
> breaking the current behavior of printing a message if some try to instantiate
> KVM on a system that doesn't support it.
> 
> Note that recent versions of systemd (>239) do not have trigger this behavior.
> 
> This patch will be useful at least for some using older systemd with recent Kernels.
> 
> Signed-off-by: Erwan Velu <e.velu@...teo.com>
> ---
>  arch/x86/kvm/x86.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 359fcd395132..c8a90231befe 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7308,12 +7308,12 @@ int kvm_arch_init(void *opaque)
>  	}
>  
>  	if (!ops->cpu_has_kvm_support()) {
> -		printk(KERN_ERR "kvm: no hardware support\n");
> +		pr_err_ratelimited("kvm: no hardware support\n");
>  		r = -EOPNOTSUPP;
>  		goto out;
>  	}
>  	if (ops->disabled_by_bios()) {
> -		printk(KERN_ERR "kvm: disabled by bios\n");
> +		pr_err_ratelimited("kvm: disabled by bios\n");
>  		r = -EOPNOTSUPP;
>  		goto out;
>  	}
> 

Queued, thanks.

Paolo