linux-kernel - Re: Silence compiler warning in arch/x86/kvm/emulate.c

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Date:	Fri, 19 Feb 2016 18:56:05 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Valdis.Kletnieks@...edu, Aurelien Jarno <aurelien@...el32.net>
Cc:	Gleb Natapov <gleb@...nel.org>, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Aruna Hewapathirane <aruna.hewapathirane@...il.com>
Subject: Re: Silence compiler warning in arch/x86/kvm/emulate.c

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On 19/02/2016 18:54, Valdis.Kletnieks@...edu wrote:
> la can get changed here - but there's 2 cases to consider.  If it's
> in a 32-bit kernel, anding with -1 is a no-op.
> 
> Now if we're on a 64-bit kernel, the 'and' clears the high 32
> bits.
> 
> But under what conditions is 'la' a 64-bit quantity that has any
> bits set in the high 32 bits (meaning it's a pointer to something 
> over the 4G line) - but it's still valid to smash those bits?

That can happen for example if there is a non-zero segment base.  Then
the linear address wraps at 4G.

Paolo
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