On Thu, Jul 19, 2012 at 01:32:59PM +0300, Avi Kivity wrote:
> On 07/19/2012 10:40 AM, Gleb Natapov wrote:
> > The function will be used outside of the emulator.
> >
> > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
> > ---
> > arch/x86/include/asm/kvm_emulate.h | 16 +++++
> > arch/x86/kvm/emulate.c | 114 ++++++++++++++++++++----------------
> > 2 files changed, 79 insertions(+), 51 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> > index 7c276ca..9ce651b 100644
> > --- a/arch/x86/include/asm/kvm_emulate.h
> > +++ b/arch/x86/include/asm/kvm_emulate.h
> > @@ -374,6 +374,21 @@ enum x86_intercept {
> > nr_x86_intercepts
> > };
> >
> > +struct x86_linearize_params
> > +{
> > + enum x86emul_mode mode;
> > + ulong ea;
> > + unsigned size;
> > + unsigned seg;
> > + struct desc_struct desc;
> > + u16 sel;
> > + bool usable;
> > + bool write;
> > + bool fetch;
> > + u8 ad_bytes;
> > + unsigned cpl;
> > +};
> > +
> > @@ -470,14 +470,6 @@ static void set_seg_override(struct x86_emulate_ctxt *ctxt, int seg)
> > ctxt->seg_override = seg;
> > }
> >
> > -static unsigned long seg_base(struct x86_emulate_ctxt *ctxt, int seg)
> > -{
> > - if (ctxt->mode == X86EMUL_MODE_PROT64 && seg < VCPU_SREG_FS)
> > - return 0;
> > -
> > - return ctxt->ops->get_cached_segment_base(ctxt, seg);
> > -}
> > -
>
> > +int x86_linearize(struct x86_linearize_params *p, ulong *linear)
> > {
> > - struct desc_struct desc;
> > - bool usable;
> > ulong la;
> > u32 lim;
> > - u16 sel;
> > unsigned cpl, rpl;
> >
> > - la = seg_base(ctxt, addr.seg) + addr.ea;
> > - switch (ctxt->mode) {
> > + la = get_desc_base(&p->desc) + p->ea;
>
> This makes 64-bit mode slower, since before the patch it avoided reading
> the segment base for non-fs/gs segments, and only read the segment base
> for fs/gs. After the patch we always execute 4 VMREADs (and decode the
> results).
>
That's easy to fix by making caller prepare fake desc if mode is 64-bit
and segment is non-fs/gs. The question is if this even measurable?
--
Gleb.
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