Re: [PATCH] x86: svm: make wbinvd faster

[Joel Schopp]

On 03/02/2015 10:03 AM, Radim KrÄmÃÅ wrote:
> 2015-03-02 10:25-0500, Bandan Das:
> > Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx> writes:
> > > 2015-03-01 21:29-0500, Bandan Das:
> > > > Joel Schopp <joel.schopp@xxxxxxx> writes:
> > > > > +static int wbinvd_interception(struct vcpu_svm *svm)
> > > > > +{
> > > > > +	kvm_emulate_wbinvd(&svm->vcpu);
> > > > > +	skip_emulated_instruction(&svm->vcpu);
> > > > > +	return 1;
> > > > > +}
> > > > Can't we merge this to kvm_emulate_wbinvd, and just call that function
> > > > directly for both vmx and svm ?
> > > kvm_emulate_wbinvd() lives in x86.c and skip_emulated_instruction() is
> > > from svm.c/vmx.c:  so we'd have to create a new x86 op and change the
> > > emulator code as well ... it's probably better like this.
> > There's already one - kvm_x86_ops->skip_emulated_instruction
> My bad, its usage is inconsistent and I only looked at two close
> interceptions where it was used ... kvm_emulate_cpuid() calls
> kvm_x86_ops->skip_emulated_instruction(), while kvm_emulate_halt() and
> kvm_emulate_hypercall() need an external skip.
>
> We do "skip" the instruction with kvm_emulate(), so automatically
> skipping the instruction on kvm_emulate_*() makes sense:
>   1. rename kvm_emulate_halt() and kvm_emulate_wbinvd() to accommodate
>      callers that don't want to skip
>   2. introduce kvm_emulate_{halt,wbinvd}() and move the skip to to
>      kvm_emulate_{halt,wbinvd,hypercall}()
>
> The alternative is to remove kvm_x86_ops->skip_emulated_instruction():
>   1. remove skip from kvm_emulate_cpuid() and modify callers
>   2. move kvm_complete_insn_gp to a header file and use
>      skip_emulated_instruction directly
>   3. remove unused kvm_x86_ops->skip_emulated_instruction()
>
> Which one do you prefer?
I prefer renaming them,  ie kvm_emulate_wbinvd_noskip(), and making the 
existing ones, ie kvm_emulate_wbinvd() call the noskip verion and add a 
skip similar to how wbinvd_interception above does.  I can send out a 
patch later today with that rework.
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