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

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Message-ID: <5622c0ac-236f-4e3e-a132-c8d3bd8fadc4@redhat.com>
Date:   Mon, 1 Jul 2019 14:02:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Li Wang <liwang@...hat.com>, ricardo.neri-calderon@...ux.intel.com,
        tglx@...utronix.de, kernellwp@...il.com, ricardo.neri@...el.com,
        pengfei.xu@...el.com
Cc:     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 09:50, Li Wang wrote:
> Hello there,
> 
> LTP/umip_basic_test get failed on KVM UMIP
> system(kernel-v5.2-rc4.x86_64). The test is only trying to do
>      asm volatile("smsw %0\n" : "=m" (val));
> and expect to get SIGSEGV in this SMSW operation, but it exits with 0
> unexpectedly.

In addition to what Thomas said, perhaps you are using a host that does
*not* have UMIP, and configuring KVM to emulate it(*).  In that case, it
is not possible to intercept SMSW, and therefore it will incorrectly
succeed.

Paolo

(*) 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.