linux-kernel - Re: [PATCH] KVM: fix sil/dil/bpl/spl in the mod/rm fields

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Date:	Mon, 3 Jun 2013 13:25:30 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: fix sil/dil/bpl/spl in the mod/rm fields

On Thu, May 30, 2013 at 05:34:21PM +0200, Paolo Bonzini wrote:
> Il 30/05/2013 16:35, Paolo Bonzini ha scritto:
> > The x86-64 extended low-byte registers were fetched correctly from reg,
> > but not from mod/rm.
> > 
> > This fixes another bug in the boot of RHEL5.9 64-bit, but it is still
> > not enough.
> 
> Well, it is enough but it takes 2 minutes to reach the point where
> hardware virtualization is used.  It is doing a lot of stuff in
> emulation mode because FS and GS have leftovers from the A20 test:
> 
> FS =0000 0000000000000000 0000ffff 00009300 DPL=0 DS16 [-WA]
> GS =ffff 00000000000ffff0 0000ffff 00009300 DPL=0 DS16 [-WA]
> 
> 0x00000000000113be:  in     $0x92,%al
> 0x00000000000113c0:  or     $0x2,%al
> 0x00000000000113c2:  out    %al,$0x92
> 0x00000000000113c4:  xor    %ax,%ax
> 0x00000000000113c6:  mov    %ax,%fs
> 0x00000000000113c8:  dec    %ax
> 0x00000000000113c9:  mov    %ax,%gs
> 0x00000000000113cb:  inc    %ax
> 0x00000000000113cc:  mov    %ax,%fs:0x200
> 0x00000000000113d0:  cmp    %gs:0x210,%ax
> 0x00000000000113d5:  je     0x113cb
> 
This is 16 bit code that sets them up. So 32bit transition code does not
reload them?

> The DPL < RPL test fails.  Any ideas?  Should we introduce a new
> intermediate value for emulate_invalid_guest_state (0=none, 1=some, 2=full)?
> 
> Paolo
> 
> > Cc: gnatapov@...hat.com
> > Cc: kvm@...r.kernel.org
> > Cc: <stable@...r.kernel.org> # 3.9
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> >  arch/x86/kvm/emulate.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> > index aa68106..028b34f 100644
> > --- a/arch/x86/kvm/emulate.c
> > +++ b/arch/x86/kvm/emulate.c
> > @@ -1239,9 +1239,12 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
> >  	ctxt->modrm_seg = VCPU_SREG_DS;
> >  
> >  	if (ctxt->modrm_mod == 3) {
> > +		int highbyte_regs = ctxt->rex_prefix == 0;
> > +
> >  		op->type = OP_REG;
> >  		op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
> > -		op->addr.reg = decode_register(ctxt, ctxt->modrm_rm, ctxt->d & ByteOp);
> > +		op->addr.reg = decode_register(ctxt, ctxt->modrm_rm,
> > +					       highbyte_regs && (ctxt->d & ByteOp));
> >  		if (ctxt->d & Sse) {
> >  			op->type = OP_XMM;
> >  			op->bytes = 16;
> > 

--
			Gleb.
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