On 14.03.2025 21:49, Andrew Cooper wrote:
> ... which is more consise than the opencoded form, and more efficient when
> compiled.
>
> For production VMs, ~100% of emulations are simple MOVs, so it is likely that
> there are no segments to write back.
>
> Furthermore, now that find_{first,next}_bit() are no longer in use, the
> seg_reg_{accessed,dirty} fields aren't forced to be unsigned long, although
> they do need to remain unsigned int because of __set_bit() elsewhere.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>
> I still can't persuade GCC to do the early exit prior to establishing the
> stack frame, and unlike do_livepatch_work(), it's not critical enough to
> require noinline games.
Then is ...
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -3022,18 +3022,16 @@ void hvm_emulate_init_per_insn(
> void hvm_emulate_writeback(
> struct hvm_emulate_ctxt *hvmemul_ctxt)
> {
> - enum x86_segment seg;
> + struct vcpu *curr;
> + unsigned int dirty = hvmemul_ctxt->seg_reg_dirty;
>
> - seg = find_first_bit(&hvmemul_ctxt->seg_reg_dirty,
> - ARRAY_SIZE(hvmemul_ctxt->seg_reg));
> + if ( likely(!dirty) )
> + return;
... this worthwhile at all? I'm surprised anyway that I see you use likely()
here, when generally you argue against its use.
Jan
