From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] kvm: don't take vcpu mutex for obviously invalid vcpu
 ioctls
Date: Mon, 22 Sep 2014 12:50:06 +0200
Message-ID: <541FFEDE.9030800@redhat.com>
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To: David Matlack <dmatlack@google.com>,
	Gleb Natapov <gleb@kernel.org>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
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Il 20/09/2014 01:03, David Matlack ha scritto:
> vcpu ioctls can hang the calling thread if issued while a vcpu is
> running. If we know ioctl is going to be rejected as invalid anyway,
> we can fail before trying to take the vcpu mutex.
> 
> This patch does not change functionality, it just makes invalid ioctls
> fail faster.
> 
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>  virt/kvm/kvm_main.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 96ec622..f9234e5 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -52,6 +52,7 @@
>  
>  #include <asm/processor.h>
>  #include <asm/io.h>
> +#include <asm/ioctl.h>
>  #include <asm/uaccess.h>
>  #include <asm/pgtable.h>
>  
> @@ -1975,6 +1976,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
>  	if (vcpu->kvm->mm != current->mm)
>  		return -EIO;
>  
> +	if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
> +		return -EINVAL;
> +
>  #if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
>  	/*
>  	 * Special cases: vcpu ioctls that are asynchronous to vcpu execution,
> 

Thanks, applying this patch.

Paolo