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

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Date:   Tue, 2 Jul 2019 16:40:18 +0800
From:   Pengfei Xu <pengfei.xu@...el.com>
To:     Li Wang <liwang@...hat.com>
Cc:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tglx@...utronix.de,
        kernellwp@...il.com, ricardo.neri@...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

Seems no issue now.

Thanks all.

On 2019-07-02 at 09:52:39 +0800, Li Wang wrote:
> On Tue, Jul 2, 2019 at 12:04 AM Ricardo Neri <
> ricardo.neri-calderon@...ux.intel.com> wrote:
> 
> > On Mon, Jul 01, 2019 at 08:57:28PM +0800, Li Wang wrote:
> > > On Mon, Jul 1, 2019 at 8:02 PM Paolo Bonzini <pbonzini@...hat.com>
> > wrote:
> > >
> > > > 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.
> > > >
> > >
> > > Right, I checked the host system, and confirmed that CPU doesn't support
> > > UMIP.
> > >
> > > >
> > > > 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.
> > > >
> > > Good to know this, is there any document for that declaration? It seems
> > > neither LTP issue nor kernel bug here. But anyway we'd better do
> > something
> > > to avoid the error in the test.
> >
> > The test case already checks for umip in /proc/cpuinfo, right? And in
> > long mode it always expects a SIGSEGV signal. If you did not add -cpu
> > host,+umip,
> > how come umip was present in /proc/cpuinfo?
> >
> 
> Yes, right.
> 
> But the KVM guest is not customized in manual, I reserved that system for
> automation test and did not aware of the '-cpu host,+umip,' parameter until
> Paolo points it out. In the last email, I was hoping to find a way to
> recognize this situation for the LTP test intelligently.
> 
> Thank you all for a reply to this.
> 
> -- 
> Regards,
> Li Wang