linux-kernel - Re: [PATCH] KVM: x86: handle wrap around 32-bit address space

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Message-ID: <2f471fbc-99fb-1a85-8f9f-c276c897f518@redhat.com>
Date:   Thu, 30 Apr 2020 14:45:19 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Jim Mattson' <jmattson@...gle.com>
Cc:     'LKML' <linux-kernel@...r.kernel.org>,
        'kvm list' <kvm@...r.kernel.org>,
        'Sean Christopherson' <sean.j.christopherson@...el.com>,
        'Joerg Roedel' <joro@...tes.org>,
        "'everdox@...il.com'" <everdox@...il.com>
Subject: Re: [PATCH] KVM: x86: handle wrap around 32-bit address space

On 29/04/20 10:56, David Laight wrote:
>>>> +               if (unlikely(((rip ^ orig_rip) >> 31) == 3) && !is_64_bit_mode(vcpu))
>> Isn't the more obvious:
>> 	if (((rip ^ orig_rip) & 1ull << 32) ...
>> equivalent?

This one would not (it would also detect carry on high memory addresses,
not just 0x7fffffff to 0x80000000)...

> Actually not even being clever, how about:
> 	if (orig_rip < (1ull << 32) && unlikely(rip >= (1ull << 32)) && ...

... but yes this one would be equivalent.

Paolo