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

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Date:   Tue, 25 Feb 2020 16:09:48 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.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

Paolo Bonzini <pbonzini@...hat.com> writes:

> 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 suggested -EINVAL because issuing KVM_GET_SUPPORTED_CPUID with nent=0
looks more like a completely invalid input and not 'too many
entries'(-E2BIG) to me (but -E2BIG is already there, let's keep it, it's
not a big deal).

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

We're agreed with Sean on a few cosmetic changes in other patches of
this series, wait for v2)

-- 
Vitaly