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

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Date:   Wed, 29 Apr 2020 08:56:12 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jim Mattson' <jmattson@...gle.com>,
        'Paolo Bonzini' <pbonzini@...hat.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

From: David Laight
> Sent: 29 April 2020 09:50
> From: Jim Mattson
> > Sent: 28 April 2020 01:29
> > On Mon, Apr 27, 2020 at 9:59 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
> > >
> > > KVM is not handling the case where EIP wraps around the 32-bit address
> > > space (that is, outside long mode).  This is needed both in vmx.c
> > > and in emulate.c.  SVM with NRIPS is okay, but it can still print
> > > an error to dmesg due to integer overflow.
> ...
> > > +               if (unlikely(((rip ^ orig_rip) >> 31) == 3) && !is_64_bit_mode(vcpu))
> 
> Isn't the more obvious:
> 	if (((rip ^ orig_rip) & 1ull << 32) ...
> equivalent?

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

	David

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