Re: [PATCH v3] KVM: x86 emulator: access GPRs on demand

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Aug 23, 2012 at 05:14:27AM -0300, Marcelo Tosatti wrote:
> On Sun, Aug 19, 2012 at 12:32:36PM +0300, Avi Kivity wrote:
> > On 08/17/2012 08:29 PM, Marcelo Tosatti wrote:
> > > On Thu, Aug 16, 2012 at 05:54:49PM +0300, Avi Kivity wrote:
> > >> Instead of populating the the entire register file, read in registers
> > >> as they are accessed, and write back only the modified ones.  This
> > >> saves a VMREAD and VMWRITE on Intel (for rsp, since it is not usually
> > >> used during emulation), and a two 128-byte copies for the registers.
> > >> 
> > > 
> > >> @@ -2715,14 +2764,17 @@ int emulator_task_switch(struct x86_emulate_ctxt *ctxt,
> > >>  {
> > >>  	int rc;
> > >>  
> > >> +	invalidate_registers(ctxt);
> > >>  	ctxt->_eip = ctxt->eip;
> > >>  	ctxt->dst.type = OP_NONE;
> > >>  
> > >>  	rc = emulator_do_task_switch(ctxt, tss_selector, idt_index, reason,
> > >>  				     has_error_code, error_code);
> > >>  
> > >> -	if (rc == X86EMUL_CONTINUE)
> > >> +	if (rc == X86EMUL_CONTINUE) {
> > >>  		ctxt->eip = ctxt->_eip;
> > >> +		writeback_registers(ctxt);
> > >> +	}
> > >>  
> > >>  	return (rc == X86EMUL_UNHANDLEABLE) ? EMULATION_FAILED : EMULATION_OK;
> > >>  }
> > > 
> > > 
> > > No clear point when emulator register cache is active, when it is
> > > not (AFAICS this patch does not invalidate registers on emulation start
> > > (the above being one of the exceptions) does not clear valid bit on
> > > writeback-to-vcpu-cache on emulation exit).
> > 
> > It is cleared when emulation starts.  For the non-insn-emulation entry
> > points, there is an explicit invalidate.  For the emulation entry point,
> > there is a memset() that clears everything up to _regs, which includes
> > the cache.  This discrepancy isn't nice, but it preexists.  I don't know
> > whether we should decompose the memset() or not, it is rather efficient.
> > 
> > > 
> > > Concern is that emulator can start with cached registers marked as valid 
> > > but in fact are invalid from previous emulation round.
> > > 
> > > Maybe move invalidate() to init_emulate_ctxt?
> > > 
> > 
> > See the memset() in init_decode_cache().
> 
> Right. Applied, thanks.

Actually, had to revert because autotest was failing. 

Now it rejects:

4 out of 49 hunks FAILED -- saving rejects to file
arch/x86/kvm/emulate.c.rej

Please regenerate.