[LTP] [Kernel BUG?] SMSW operation get success on UMIP KVM guest

[Li Wang]

On Tue, Jul 2, 2019 at 12:04 AM Ricardo Neri <
ricardo.neri-calderon@linux.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@redhat.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
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