linux-kernel - Re: [PATCH 02/61] KVM: x86: Refactor loop around do_cpuid

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Date:   Tue, 25 Feb 2020 15:37:56 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/61] KVM: x86: Refactor loop around do_cpuid_func() to
 separate helper

On 07/02/20 20:53, Sean Christopherson wrote:
> 
>> 2) Return -EINVAL instead.
> I agree that it _should_ be -EINVAL, but I just don't think it's worth
> the possibility of breaking (stupid) userspace that was doing something
> like:
> 
> 	for (i = 0; i < max_cpuid_size; i++) {
> 		cpuid.nent = i;
> 
> 		r = ioctl(fd, KVM_GET_SUPPORTED_CPUID, &cpuid);
> 		if (!r || r != -E2BIG)
> 			break;
> 	}
> 

Apart from the stupidity of the above case, why would it be EINVAL?

I can do the change to drop the initializer when applying.

Paolo