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Date:   Thu, 11 Apr 2019 06:44:51 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Nadav Amit <nadav.amit@gmail.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org
Subject: Re: [kvm-unit-tests PATCH] x86: Fix wrong test for 5-level page-table
Message-ID: <20190411134451.GB29427@linux.intel.com>
References: <20190410211334.13391-1-nadav.amit@gmail.com>
 <20190411134104.GA29427@linux.intel.com>
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On Thu, Apr 11, 2019 at 06:41:05AM -0700, Sean Christopherson wrote:
> On Wed, Apr 10, 2019 at 02:13:34PM -0700, Nadav Amit wrote:
> > Untested, but clearly bit 12 is the one that needs to be tested.
> > 
> > Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
> > ---
> >  x86/cstart64.S | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/x86/cstart64.S b/x86/cstart64.S
> > index 21db10f..8626f02 100644
> > --- a/x86/cstart64.S
> > +++ b/x86/cstart64.S
> > @@ -243,7 +243,7 @@ start64:
> >  setup_5level_page_table:
> >  	/* Check if 5-level paging has already enabled */
> >  	mov %cr4, %rax
> > -	test $12, %eax
> > +	bt $12, %eax
> >  	jnz lvl5
> 
> Unfortunately BT doesn't affect RFLAGS.ZF, so 'jnz' needs to be changed
> to 'jc'.  Or alternatively, do 'test $1000, %eax'.

And of course that should be $0x1000...