Re: [PATCH 2/2] Provide fast path for "rep ins" emulation if possible.

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jun 05, 2012 at 07:07:39PM +0300, Avi Kivity wrote:
> > +
> > +	count = (PAGE_SIZE - offset_in_page(linear_addr))/size;
> > +
> > +	if (count == 0) /* 'in' crosses page boundry */
> > +		return EMULATE_FAIL;
> > +
> > +	count = min(count, rcx);
> > +
> > +	r = __kvm_fast_string_pio_in(vcpu, size, port, linear_addr, count);
> > +
> > +	if (r != EMULATE_DO_MMIO)
> > +		return r;
> > +
> > +	vcpu->arch.fast_string_pio_ctxt.linear_addr = linear_addr;
> > +	vcpu->arch.complete_userspace_io = complete_fast_string_pio;
> > +	return EMULATE_DO_MMIO;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_fast_string_pio_in);
> 
> Perhaps a better way to do it is to move the code into the emulator,
> which already handles all the checks and masks, and just avoid
> x86_decode_insn()/x86_emulate_insn().
> 
I do not see how it would be better. Emulator works on different data
structures that should be prepared and the only functions that we can
reuse (as far as I see) are register_address_increment() and ad_mask()
anyway.

--
			Gleb.