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

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Date:   Wed, 14 Feb 2018 11:10:22 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        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 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.

Paolo