linux-kernel - Re: [patch] kvm: suppress KVM_SET_GSI

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Date:   Wed, 14 Feb 2018 12:14:45 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        David Rientjes <rientjes@...gle.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [patch] kvm: suppress KVM_SET_GSI_ROUTING allocation failure



On 02/14/2018 11:10 AM, Paolo Bonzini wrote:
> On 14/02/2018 02:03, David Rientjes wrote:
>> On Tue, 13 Feb 2018, Paolo Bonzini wrote:
>>
>>>>> The KVM_SET_GSI_ROUTING ioctl does a vmalloc() of
>>>>> sizeof(struct kvm_irq_routing_entry) multiplied by a user-supplied value.
>>>>> This can be up to 4096 entries on architectures such as arm64 and s390
>>>>> (and the upper bound may be increased on s390 eventually).
>>>>>
>>>>> This can produce a vmalloc allocation failure warning:
>>>>>
>>>> [...]
>>>>>  kvm_vm_ioctl+0x910/0x15e0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4153
>>>>
>>>>                                                                        ^^^^^
>>>>
>>>>> @@ -3063,7 +3063,8 @@ static long kvm_vm_ioctl(struct file *filp,
>>>>
>>>>       ^^^^^
>>>>
>>>>
>>>> Are you sure that you got the right vmalloc?
>>>
>>> Nice catch!  But well, it's the only one in the whole file. :)
>>>
>>> That seems very much like an old patch then.  I'm unqueuing it.
>>>
>>
>> It's not a catch at all, the fact that I saw this warning with an older 
>> kernel for KVM_SET_GSI_ROUTING doesn't mean that I can't patch it with an 
>> upstream kernel.  Would you prefer I remove the stack trace completely?
> 
> The upstream kernel doesn't warn.  It checks "if (routing.nr)" before
> calling vmalloc.

It will warn of the vmalloc space is really exhausted. But then I really ask
myself if we really want to suppress this warning. This should be a big
ALERT to the host admin.