linux-kernel - Re: [PATCH 01/61] KVM: x86: Return -E2BIG when KVM_GET_SUPPORTED

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Message-ID: <70f9ef36-b180-79d4-7d9a-8df8d6219122@redhat.com>
Date:   Tue, 25 Feb 2020 15:36:03 +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 01/61] KVM: x86: Return -E2BIG when
 KVM_GET_SUPPORTED_CPUID hits max entries

On 03/02/20 16:59, Sean Christopherson wrote:
> 
>> In particular, here the change is both the
>> return value and the fact that we don't do copy_to_user() anymore so I
>> think it's possible to meet a userspace which is going to get broken by
>> the change.
> Ugh, yeah, it would be possible.  Qemu (retries), CrosVM (hardcoded to
> 256 entries) and Firecracker (doesn't use the ioctl()) are all ok,
> hopefully all other VMMs used in production environments follow suit.
> 

Also: lkvm and selftests both hardcode the limit to 100.

Both would be broken by this change, but as long as the limit is < 100
now it is fine to change.

Paolo