linux-kernel - Re: [Kernel BUG?] SMSW operation get success on UMIP KVM guest

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Date:   Mon, 1 Jul 2019 19:30:50 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Li Wang <liwang@...hat.com>, tglx@...utronix.de,
        kernellwp@...il.com, ricardo.neri@...el.com, pengfei.xu@...el.com,
        LTP List <ltp@...ts.linux.it>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ping Fang <pifang@...hat.com>
Subject: Re: [Kernel BUG?] SMSW operation get success on UMIP KVM guest

On 01/07/19 16:53, Ricardo Neri wrote:
>>
>> (*) before the x86 people jump at me, this won't happen unless you
>> explicitly pass an option to QEMU, such as "-cpu host,+umip". :)  The
>> incorrect emulation of SMSW when CR4.UMIP=1 is why.
> Paolo, what do you mean by the incorrect emulation of SMSW?

When KVM tries to emulate UMIP on a system that doesn't have it, SMSW
won't cause a #GP.  The processor is simply not able to trap to the
hypervisor on SMSW (unlike SGDT/SIDT/SLDT/STR), so it's impossible to do
better.

Paolo