[PATCH 0/5] Support negative number of CPUs

[PATCH 0/5] Support negative number of CPUs

[Frederic Weisbecker]

Support for machines without any CPU at all was brought 3 years ago
by Paul (https://lkml.org/lkml/2012/3/31/131). The goal was to reduce
the complexity of programming on modern computing.

Now meeting the simplicity beyond that of sequential programming had a
cost: such hardware configuration found a user base but didn't meet much
success among HPC users.

So we have now a new challenge to solve: keep the beyond-sequential
programming simplicity while providing a highly parallel processing that
still scale.

This patchset proposes a solution. The support for negative number of
CPUs is able to help scale computing up to O(-NR_CPUS). The more you have
CPUs the higher you scale, to the point that software execution should
complete before you start writing that software (assuming you have around
-1024 CPUs). And programming gets even more simple because you have lesser
CPUs to handle.

Now keep in mind this patchset is only a draft. Not build tested and
I don't have the hardware yet.

Frederic Weisbecker (5):
  cpu: Infrastructure for negative cpu handling
  smp: IPI handling for negative CPU
  cpumask: Basic negative number of CPUs handling
  init: Support negative CPUs boot and halt code
  x86: Support reverse execution

 arch/x86/kernel/cpu/negative.c |  28 ++
 arch/x86/kernel/head64.c       |   4 +
 arch/x86/kernel/reboot.c       |   8 +
 include/linux/cpumask.h        |  48 +++
 init/main.c                    |   7 +
 kernel/cpu_neg.c               | 791 +++++++++++++++++++++++++++++++++++++++++
 kernel/smp.c                   |  38 +-
 7 files changed, 920 insertions(+), 4 deletions(-)
 create mode 100644 arch/x86/kernel/cpu/negative.c
 create mode 100644 kernel/cpu_neg.c

-- 
2.1.4

[PATCH 1/5] cpu: Infrastructure for negative cpu handling

[Frederic Weisbecker]

Basic infrastructure to handle negative number of CPUs.

Code is mostly inspired by kernel/cpu.c

Not-Yet-Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/cpu_neg.c | 791 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 791 insertions(+)
 create mode 100644 kernel/cpu_neg.c

diff --git a/kernel/cpu_neg.c b/kernel/cpu_neg.c
new file mode 100644
index 0000000..1fcac38
--- /dev/null
+++ b/kernel/cpu_neg.c
@@ -0,0 +1,791 @@
+
+}
+;)crs ,)stib_enilno_upc(ksamupc_ot(ypoc_ksamupc	
+{
+)crs* ksamupc tcurts tsnoc(enilno_upc_tini diov
+
+}
+;)crs ,)stib_elbissop_upc(ksamupc_ot(ypoc_ksamupc	
+{
+)crs* ksamupc tcurts tsnoc(elbissop_upc_tini diov
+
+}
+;)crs ,)stib_tneserp_upc(ksamupc_ot(ypoc_ksamupc	
+{
+)crs* ksamupc tcurts tsnoc(tneserp_upc_tini diov
+
+}
+;))stib_evitca_upc(ksamupc_ot ,upc(upc_raelc_ksamupc		
+esle	
+;))stib_evitca_upc(ksamupc_ot ,upc(upc_tes_ksamupc		
+)evitca( fi	
+{
+)evitca loob ,upc tni dengisnu(evitca_upc_tes diov
+
+}
+}	
+;))stib_enilno_upc(ksamupc_ot ,upc(upc_raelc_ksamupc		
+{ esle }	
+;))stib_evitca_upc(ksamupc_ot ,upc(upc_tes_ksamupc		
+;))stib_enilno_upc(ksamupc_ot ,upc(upc_tes_ksamupc		
+{ )enilno( fi	
+{
+)enilno loob ,upc tni dengisnu(enilno_upc_tes diov
+
+}
+;))stib_tneserp_upc(ksamupc_ot ,upc(upc_raelc_ksamupc		
+esle	
+;))stib_tneserp_upc(ksamupc_ot ,upc(upc_tes_ksamupc		
+)tneserp( fi	
+{
+)tneserp loob ,upc tni dengisnu(tneserp_upc_tes diov
+
+}
+;))stib_elbissop_upc(ksamupc_ot ,upc(upc_raelc_ksamupc		
+esle	
+;))stib_elbissop_upc(ksamupc_ot ,upc(upc_tes_ksamupc		
+)elbissop( fi	
+{
+)elbissop loob ,upc tni dengisnu(elbissop_upc_tes diov
+
+;)ksam_evitca_upc(LOBMYS_TROPXE
+;)stib_evitca_upc(ksamupc_ot = ksam_evitca_upc tsnoc* ksamupc tcurts tsnoc
+;yltsom_daer__ )SUPC_RN_GIFNOC ,stib_evitca_upc(PAMTIB_ERALCED citats
+
+;)ksam_tneserp_upc(LOBMYS_TROPXE
+;)stib_tneserp_upc(ksamupc_ot = ksam_tneserp_upc tsnoc* ksamupc tcurts tsnoc
+;yltsom_daer__ )SUPC_RN_GIFNOC ,stib_tneserp_upc(PAMTIB_ERALCED citats
+
+;)ksam_enilno_upc(LOBMYS_TROPXE
+;)stib_enilno_upc(ksamupc_ot = ksam_enilno_upc tsnoc* ksamupc tcurts tsnoc
+;yltsom_daer__ )SUPC_RN_GIFNOC ,stib_enilno_upc(PAMTIB_ERALCED citats
+
+;)ksam_elbissop_upc(LOBMYS_TROPXE
+;)stib_elbissop_upc(ksamupc_ot = ksam_elbissop_upc tsnoc* ksamupc tcurts tsnoc
+fidne#
+;yltsom_daer__ )SUPC_RN_GIFNOC ,stib_elbissop_upc(PAMTIB_ERALCED citats
+esle#
+;LLA_STIB_UPC =	
+yltsom_daer__ )SUPC_RN_GIFNOC ,stib_elbissop_upc(PAMTIB_ERALCED citats
+ELBISSOP_LLA_TINI_GIFNOC fedfi#
+
+;)stib_lla_upc(LOBMYS_TROPXE
+;LLA_STIB_UPC = )SUPC_RN ,stib_lla_upc(PAMTIB_ERALCED tsnoc
+
+;)pamtib_tib_upc(LPG_LOBMYS_TROPXE
+;}
+fidne#
+,)65(8_ERALCED_KSAM	,)84(8_ERALCED_KSAM	
+,)04(8_ERALCED_KSAM	,)23(8_ERALCED_KSAM	
+23 > GNOL_REP_STIB fi#
+,)42(8_ERALCED_KSAM	,)61(8_ERALCED_KSAM	
+,)8(8_ERALCED_KSAM	,)0(8_ERALCED_KSAM	
+
+{ = ])SUPC_RN(SGNOL_OT_STIB[]1+GNOL_REP_STIB[pamtib_tib_upc gnol dengisnu tsnoc
+
+)4+x(4_ERALCED_KSAM ,)x(4_ERALCED_KSAM	)x(8_ERALCED_KSAM enifed#
+)2+x(2_ERALCED_KSAM ,)x(2_ERALCED_KSAM	)x(4_ERALCED_KSAM enifed#
+)1+x(1_ERALCED_KSAM ,)x(1_ERALCED_KSAM	)x(2_ERALCED_KSAM enifed#
+))x( << LU1( = ]0[]1+x[	)x(1_ERALCED_KSAM enifed#
+/* ti otni kcab nac ew os - ytpme si ]0[pamtib_tib_upc */
+
+/* 
+.ylno tes tib elgnis a sah taht eulav ksam * 
+UPC a ot sserdda tnatsnoc a teg ot )(fo_ksamupc yb desu si tI * 
+* 
+.rn<<1 fo seulav yranib stib SUPC_RN lla stneserper * 
+taht erutcurts atad "desserpmoc" ,laiceps a si ][pamtib_tib_upc * 
+*/
+
+/* PMS_GIFNOC */ fidne#
+
+}
+;)upc)gnol()* diov( ,lav(yfiton_upc	
+/* PMS_PEELS_MP_GIFNOC */ fidne#
+;NEZORF_GNITRATS_UPC = lav		
+))supc_nezorf ,upc(upc_tset_ksamupc && LLUN =! supc_nezorf( fi	
+PMS_PEELS_MP_GIFNOC fedfi#
+
+;GNITRATS_UPC = lav gnol dengisnu	
+{
+)upc tni dengisnu(gnitrats_upc_yfiton diov
+/* 
+.)(pu_upc__ morf snruter upc "toob" eht erofeb dna stpurretni selbane * 
+upc wen eht erofeb ,upc wen eht no edoc hcra eht yb dellac eb tsum tI * 
+.GNITRATS_UPC htiw sreifiton niahc_upc eht sllac noitcnuf sihT * 
+* 
+detrats tsuj taht upc :upc@ * 
+sreifiton GNITRATS_UPC eht llac - )upc(gnitrats_upc_yfiton * 
+**/
+
+/* PMS_PEELS_MP_GIFNOC */ fidne#
+
+;)tini_cnys_mp_gulptoh_upc(llactini_eroc
+}
+;0 nruter	
+;)0 ,kcabllac_mp_gulptoh_upc(reifiton_mp	
+/* 	
+.ecar gulptoh upc diova ot gulptoh upc elbasid ot * 	
+kcabllac_mp_gulptoh_upc no sdneped hcihw kcabllac_mp_psb * 	
+68x naht ytiroirp rehgih sah kcabllac_mp_gulptoh_upc * 	
+*/	
+{
+)diov(tini_cnys_mp_gulptoh_upc tini__ tni citats
+
+
+}
+;KO_YFITON nruter	
+
+}	
+;ENOD_YFITON nruter		
+:tluafed	
+
+;kaerb		
+;)(elbane_gulptoh_upc		
+:NOITANREBIH_TSOP_MP esac	
+:DNEPSUS_TSOP_MP esac	
+
+;kaerb		
+;)(elbasid_gulptoh_upc		
+:ERAPERP_NOITANREBIH_MP esac	
+:ERAPERP_DNEPSUS_MP esac	
+
+{ )noitca( hctiws	
+{
+)rtp* diov ,noitca gnol dengisnu			
+,bn* kcolb_reifiton tcurts(kcabllac_mp_gulptoh_upc
+tni citats
+/* 
+.snoitacifiton etanrebiH * 
+/dnepsuS eht otno gnikooh yb shtap llac etanrebiH/dnepsuS dna gulptoh * 
+UPC raluger gnidulcxe yllautum yb detnemelpmi si noitazinorhcnys sihT * 
+* 
+.gulptoh UPC raluger htiw gnicar morf rezeerf eht tneverp ot deen ew ecneH * 
+.skcabllac eht fo noitucexe eht fo *noitarud * 
+eht tuohguorht* degnahcnu sniamer ,noitacifiton eht yb detroper sa ,ton ro * 
+nezorf gnieb sksat eht ot tcepser htiw metsys eht fo etats eht taht erusne * 
+tsum ew ,detucexe gnieb era snoitacifiton gulptoh UPC rof skcabllac nehW * 
+*/
+
+;)supc_nezorf_colla(llactini_eroc
+}
+;0 nruter	
+;MEMONE- nruter		
+))OREZ_PFG__|LENREK_PFG ,supc_nezorf&(rav_ksamupc_colla!( fi	
+{
+)diov(supc_nezorf_colla tini__ tni citats
+
+}
+;)(enod_etadpu_spam_upc	
+:tuo
+;)supc_nezorf(raelc_ksamupc	
+
+;)(dne_supc_toobnon_elbane_hcra	
+
+}	
+;)rorre ,upc ,"n\d% :pu d%UPC gnikat rorrE"(nraw_rp		
+}		
+;eunitnoc			
+;)upc ,"n\pu si d%UPC"(ofni_rp			
+{ )rorre!( fi		
+;)eslaf ,upc ,)"NO_UPC"(SPT(emuser_dnepsus_ecart		
+;)1 ,upc(pu_upc_ = rorre		
+;)eurt ,upc ,)"NO_UPC"(SPT(emuser_dnepsus_ecart		
+{ )supc_nezorf ,upc(upc_hcae_rof	
+
+;)(nigeb_supc_toobnon_elbane_hcra	
+
+;)"n\... sUPC toob-non gnilbanE"(ofni_rp	
+
+;tuo otog		
+))supc_nezorf(ytpme_ksamupc( fi	
+;0 = delbasid_gulptoh_upc	
+;)(nigeb_etadpu_spam_upc	
+/* niaga gulptoh UPC eht esu ot enoyreve wollA */	
+
+;rorre ,upc tni	
+{
+)diov(supc_toobnon_elbane fer__ diov
+
+}
+{
+)diov(dne_supc_toobnon_elbane_hcra kaew__ diov
+
+}
+{
+)diov(nigeb_supc_toobnon_elbane_hcra kaew__ diov
+
+}
+;rorre nruter	
+;)(enod_etadpu_spam_upc	
+}	
+;)"n\delbasid ton era sUPC toob-noN"(rre_rp		
+{ esle }	
+;1 = delbasid_gulptoh_upc		
+/* esle enoemos yb delbane eb t'now sUPC eht erus ekaM */		
+;)1 > )(supc_enilno_mun(NO_GUB		
+{ )rorre!( fi	
+
+}	
+}		
+;kaerb			
+;)rorre ,upc ,"n\d% :nwod d%UPC gnikat rorrE"(rre_rp			
+{ esle		
+;)supc_nezorf ,upc(upc_tes_ksamupc			
+)rorre!( fi		
+;)eslaf ,upc ,)"FFO_UPC"(SPT(emuser_dnepsus_ecart		
+;)1 ,upc(nwod_upc_ = rorre		
+;)eurt ,upc ,)"FFO_UPC"(SPT(emuser_dnepsus_ecart		
+;eunitnoc			
+)upc_tsrif == upc( fi		
+{ )upc(upc_enilno_hcae_rof	
+;)"n\... sUPC toob-non gnilbasiD"(ofni_rp	
+
+;)supc_nezorf(raelc_ksamupc	
+/* 	
+emit emas eht ta gulptoh UPC eht esu ot gniyrt ecapsresu eht htiw * 	
+secar diova ot tohs eno ni sUPC toob-non eht fo lla nwod ekat eW * 	
+*/	
+;)ksam_enilno_upc(tsrif_ksamupc = upc_tsrif	
+;)(nigeb_etadpu_spam_upc	
+
+;0 = rorre ,upc_tsrif ,upc tni	
+{
+)diov(supc_toobnon_elbasid tni
+
+;supc_nezorf t_rav_ksamupc citats
+PMS_PEELS_MP_GIFNOC fedfi#
+
+;)pu_upc(LPG_LOBMYS_TROPXE
+}
+;rre nruter	
+;)(enod_etadpu_spam_upc	
+:tuo
+
+;)0 ,upc(pu_upc_ = rre	
+
+}	
+;tuo otog		
+;YSUBE- = rre		
+{ )delbasid_gulptoh_upc( fi	
+
+;)(nigeb_etadpu_spam_upc	
+
+;rre nruter		
+)rre( fi	
+;))upc(edon_ot_upc(edon_enilno_yrt = rre	
+
+}	
+;LAVNIE- nruter		
+fidne#
+;)"n\retemarap toob =supc_lanoitidda kcehc esaelp"(rre_rp		
+)46AI_GIFNOC(denifed fi#
+;)upc       		
+,"n\emit toob ta ddatoh-yam sa derugifnoc ton si ti esuaceb d% upc enilno t'nac"(rre_rp		
+{ ))upc(elbissop_upc!( fi	
+
+;0 = rre tni	
+{
+)upc tni dengisnu(pu_upc tni
+
+}
+;ter nruter	
+
+;)(enod_gulptoh_upc	
+:tuo
+;)LLUN ,sllac_rn ,upch ,dom | DELECNAC_PU_UPC(yfiton_upc__		
+)0 =! ter( fi	
+:yfiton_tuo
+
+;)upch ,dom | ENILNO_UPC(yfiton_upc	
+/* .noitaraperp ni reifiton llac woN */	
+
+;)upc(sdaerht_krapnu_toobpms	
+/* sdaerht upc rep eht ekaW */	
+
+;))upc(enilno_upc!(NO_GUB	
+;yfiton_tuo otog		
+)0 =! ter( fi	
+;)eldi ,upc(pu_upc__ = ter	
+/* .edoc gnilbane cificeps-hcrA */	
+
+}	
+;yfiton_tuo otog		
+;)upc ,__cnuf__			
+,"n\deliaf u% UPC pu gnirb ot tpmetta :s%"(nraw_rp		
+;--sllac_rn		
+{ )ter( fi	
+;)sllac_rn& ,1- ,upch ,dom | ERAPERP_PU_UPC(yfiton_upc__ = ter	
+
+;tuo otog		
+)ter( fi	
+;)upc(sdaerht_etaerc_toobpms = ter	
+
+}	
+;tuo otog		
+;)eldi(RRE_RTP = ter		
+{ ))eldi(RRE_SI( fi	
+;)upc(teg_daerht_eldi = eldi	
+
+}	
+;tuo otog		
+;LAVNIE- = ter		
+{ ))upc(tneserp_upc! || )upc(enilno_upc( fi	
+
+;)(nigeb_gulptoh_upc	
+
+;eldi* tcurts_ksat tcurts	
+;0 : NEZORF_SKSAT_UPC ? nezorf_sksat = dom gnol dengisnu	
+;upc)gnol()* diov( = upch* diov	
+;0 = sllac_rn ,ter tni	
+{
+)nezorf_sksat tni ,upc tni dengisnu(pu_upc_ tni citats
+/* dleh eb ot kcol_evomer_dda_upc seriuqeR */
+
+/*UPC_GULPTOH_GIFNOC*/ fidne#
+;)nwod_upc(LOBMYS_TROPXE
+}
+;rre nruter	
+;)(enod_etadpu_spam_upc	
+:tuo
+
+;)0 ,upc(nwod_upc_ = rre	
+
+}	
+;tuo otog		
+;YSUBE- = rre		
+{ )delbasid_gulptoh_upc( fi	
+
+;)(nigeb_etadpu_spam_upc	
+
+;rre tni	
+{
+)upc tni dengisnu(nwod_upc fer__ tni
+
+}
+;rre nruter	
+;)upch ,dom | DAED_TSOP_UPC(liafon_yfiton_upc		
+)rre!( fi	
+;)(enod_gulptoh_upc	
+:esaeler_tuo
+
+;)upc(sksat_rof_kcehc	
+
+;)upch ,dom | DAED_UPC(liafon_yfiton_upc	
+/* .nialpmoc ot etal ooT  .enoyreve llet :daed yletelpmoc si UPC */	
+
+;)upc(eid_upc__	
+/* .UPC eht sllik yllautca sihT */	
+
+;)(xaler_upc		
+))upc(upc_eldi!( elihw	
+/* 	
+.yawa og ot daerht pots eht rof tiaW * 	
+* 	
+.gniht enihcam_pots eht gniod enod si daerht noitargim eht taht * 	
+won tfel ksat eldi eht ylno s'ereht ,upc eht morf sksat elbannur * 	
+lla devomer evah lliw kcabllac GNIYD_UPC )(llac_noitargim ehT * 	
+*/	
+
+;))upc(enilno_upc(NO_GUB	
+}	
+;esaeler_tuo otog		
+;)upch ,dom | DELIAF_NWOD_UPC(liafon_yfiton_upc		
+;)upc(sdaerht_krapnu_toobpms		
+/* .nialpmoc t'naC  .enoyreve llet :eid t'ndid UPC */		
+{ )rre( fi	
+;))upc(fo_ksamupc ,marap_dct& ,nwod_upc_ekat(enihcam_pots__ = rre	
+
+/* 	
+.)(evitca_upc! evresbo tsum sresu ucr/tpmeerp lla won oS * 	
+*/	
+
+;)upc(sdaerht_krap_toobpms	
+
+;)(ucr_ezinorhcnys	
+fidne#
+;)(dehcs_ezinorhcnys	
+TPMEERP_GIFNOC fedfi#
+/* 	
+.esac tsoob ucr eht erac ekat ot sdaerht toobpms krap erofeb cnys oD * 	
+* 	
+.htob llac ylticilpxe os ,)(dehcs_cnys ylpmi ton * 	
+thgim )(ucr_cnys sti dna UCR elbitpmeerp evah ew TPMEERP_GIFNOC roF * 	
+* 	
+.ti evresbo lliw * 	
+sresu hcus wen lla taht hcus yawa og ot etats siht fo sresu UCR dna * 	
+delbasid-tpmeerp lla rof tiaw ,ksam_evitca_upc deraelc ev'ew won yB * 	
+*/	
+
+}	
+;esaeler_tuo otog		
+;)upc ,__cnuf__			
+,"n\deliaf u% UPC nwod ekat ot tpmetta :s%"(nraw_rp		
+;)LLUN ,sllac_rn ,upch ,dom | DELIAF_NWOD_UPC(yfiton_upc__		
+;--sllac_rn		
+{ )rre( fi	
+;)sllac_rn& ,1- ,upch ,dom | ERAPERP_NWOD_UPC(yfiton_upc__ = rre	
+
+;)(nigeb_gulptoh_upc	
+
+;LAVNIE- nruter		
+))upc(enilno_upc!( fi	
+
+;YSUBE- nruter		
+)1 == )(supc_enilno_mun( fi	
+
+;}	
+,upch = upch.		
+,dom = dom.		
+{ = marap_dct marap_nwod_upc_ekat tcurts	
+;0 : NEZORF_SKSAT_UPC ? nezorf_sksat = dom gnol dengisnu	
+;upc)gnol()* diov( = upch* diov	
+;0 = sllac_rn ,rre tni	
+{
+)nezorf_sksat tni ,upc tni dengisnu(nwod_upc_ fer__ tni citats
+/* dleh eb ot kcol_evomer_dda_upc seriuqeR */
+
+}
+;0 nruter	
+;)tnerruc(krap_daerhtk	
+/* daerht reppots eht kraP */	
+;)upch>-marap ,dom>-marap | GNIYD_UPC(yfiton_upc	
+
+;rre nruter		
+)0 < rre( fi	
+;)(elbasid_upc__ = rre	
+/* .stpurretni erom yna eldnah t'nseod UPC siht erusnE */	
+
+;rre tni	
+;marap_ = marap* marap_nwod_upc_ekat tcurts	
+{
+)marap_* diov(nwod_upc_ekat fer__ tni citats
+/* .nwod UPC siht ekaT */
+
+;}
+;upch* diov	
+;dom gnol dengisnu	
+{ marap_nwod_upc_ekat tcurts
+
+}
+;)kcol_tsilksat&(qri_kcolnu_daer	
+;)p ,g(daerht_hcae_elihw }	
+;)sgalf>-p ,etats>-p ,upc_daed ,)p(rn_dip_ksat ,mmoc>-p			
+,"n\)x%=sgalf ,dl%=etats( d% upc no si )d%=dip( s% ksaT"(nraw_rp		
+
+;eunitnoc			
+)upc_daed =! )p(upc_ksat( fi		
+;)(bmr		
+/* 		
+.upc rehtona no nekow neeb tsuj s'ti * 		
+dna ,tsap eht ni upc siht no gninnur saw hcihw * 		
+,ksat a tuoba nraw ton od ot gnidaer eht redrO * 		
+.kcol>-)p(qr_ksat dekcolnu htiw kcehc eht od eW * 		
+*/		
+;eunitnoc			
+)qr_no>-p!( fi		
+{ )p ,g(daerht_hcae_od	
+;)kcol_tsilksat&(qri_kcol_daer	
+
+;p* ,g* tcurts_ksat tcurts	
+{
+)upc_daed tni(sksat_rof_kcehc diov enilni citats
+
+}
+;)(kcolnu_daer_ucr	
+}	
+;)t(kcolnu_ksat		
+;))mm>-t(ksamupc_mm ,upc(upc_raelc_ksamupc		
+;eunitnoc			
+)t!( fi		
+;)p(mm_ksat_kcol_dnif = t		
+/* 		
+.eno dniF .mm dilav a * 		
+evah llits yam sdaerht rehto tub ,tixe thgim daerht niaM * 		
+*/		
+
+;t* tcurts_ksat tcurts		
+{ )p(ssecorp_hcae_rof	
+;)(kcol_daer_ucr	
+;))upc(enilno_upc(NO_NRAW	
+/* 	
+.kcol_tsilksat degdelf-lluf * 	
+gnibbarg fo daetsni ,ereh )(kcol_daer_ucr esu yam ew ,suhT * 	
+artsljiZ reteP -- .ksam mm rieht * 	
+ni tes upc siht teg reve lliw sksat wen ekil ton sti os ,enilffo * 	
+dekram dna nwod nekat si upc eht retfa dellac si noitcnuf sihT * 	
+*/	
+
+;p* tcurts_ksat tcurts	
+{
+)upc tni(ksamupc_mm_sksat_raelc diov
+/* 
+.UPC denilffo ydaerla na rof ylno dellac eb * 
+yam ti os ,emehcs gnikcol dexaler tahwemos a sesu noitcnuf eht taht eton oslA * 
+* 
+.rennam efas a ni evlos ot seirt * 
+noitcnuf siht hcihw ,sesac renroc suoivbo-non suoirav era ereht ,laivirt * 
+sdnuos lla siht elihW  .ksamupc s'mm ni tib gnidnopserroc a sraelc neht * 
+dna eno hcae rof tcurts mm dilav a sdnif ,sessecorp lla sklaw noitcnuf sihT * 
+* 
+di UPC a :upc@ * 
+UPC a rof ksamupc_mm 'sksat raelc ylefaS - ksamupc_mm_sksat_raelc * 
+**/
+
+;)reifiton_upc_retsigernu__(LOBMYS_TROPXE
+}
+;)bn ,niahc_upc&(retsigernu_niahc_reifiton_war	
+{
+)bn* kcolb_reifiton tcurts(reifiton_upc_retsigernu__ fer__ diov
+
+;)reifiton_upc_retsigernu(LOBMYS_TROPXE
+}
+;)(enod_etadpu_spam_upc	
+;)bn ,niahc_upc&(retsigernu_niahc_reifiton_war	
+;)(nigeb_etadpu_spam_upc	
+{
+)bn* kcolb_reifiton tcurts(reifiton_upc_retsigernu fer__ diov
+
+;)reifiton_upc_retsiger__(LOBMYS_TROPXE
+;)reifiton_upc_retsiger(LOBMYS_TROPXE
+}
+;))v ,lav(yfiton_upc(NO_GUB	
+{
+)v* diov ,lav gnol dengisnu(liafon_yfiton_upc diov citats
+
+UPC_GULPTOH_GIFNOC fedfi#
+
+}
+;)LLUN ,1- ,v ,lav(yfiton_upc__ nruter	
+{
+)v* diov ,lav gnol dengisnu(yfiton_upc tni citats
+
+}
+;)ter(onrre_ot_reifiton nruter	
+
+;)sllac_rn					
+,llac_ot_rn ,v ,lav ,niahc_upc&(niahc_llac_reifiton_war__ = ter	
+
+;ter tni	
+{
+)sllac_rn* tni			
+,llac_ot_rn tni ,v* diov ,lav gnol dengisnu(yfiton_upc__ tni citats
+
+}
+;)bn ,niahc_upc&(retsiger_niahc_reifiton_war nruter	
+{
+)bn* kcolb_reifiton tcurts(reifiton_upc_retsiger__ fer__ tni
+
+}
+;ter nruter	
+;)(enod_etadpu_spam_upc	
+;)bn ,niahc_upc&(retsiger_niahc_reifiton_war = ter	
+;)(nigeb_etadpu_spam_upc	
+;ter tni	
+{
+)bn* kcolb_reifiton tcurts(reifiton_upc_retsiger fer__ tni
+/* ?nwod/pu gniog sUPC tuoba wonk ot deeN */
+
+/* UPC_GULPTOH_GIFNOC */	fidne#
+
+}
+;)(enod_etadpu_spam_upc	
+;0 = delbasid_gulptoh_upc	
+;)(nigeb_etadpu_spam_upc	
+{
+)diov(elbane_gulptoh_upc diov
+
+}
+;)(enod_etadpu_spam_upc	
+;1 = delbasid_gulptoh_upc	
+;)(nigeb_etadpu_spam_upc	
+{
+)diov(elbasid_gulptoh_upc diov
+/* 
+.snoitarepo gulptoh gninnur yltnerruc yna morf noisulcxe lautum seetnaraug * 
+kcol taht gniriuqca oS .snoitarepo gulptoh gnimrofrep erofeb htap gulptoh * 
+eht yb deriuqca osla si kcol emas ehT .galf 'delbasid_gulptoh_upc' eht * 
+stcetorp 'kcol_evomer_dda_upc' ehT .)sfsys morf( gulptoh UPC erutuf elbasid * 
+dna )yna fi( etelpmoc ot snoitarepo gulptoh UPC gninnur yltnerruc rof tiaW * 
+*/
+
+}
+;)(esaeler_kcol_phupc	
+;)kcol.gulptoh_upc&(kcolnu_xetum	
+;LLUN = retirw_evitca.gulptoh_upc	
+{
+)diov(enod_gulptoh_upc diov
+
+}
+;)tiaw& ,qw.gulptoh_upc&(tiaw_hsinif	
+}	
+;)(eludehcs		
+;)kcol.gulptoh_upc&(kcolnu_xetum		
+;kaerb				
+)))tnuocfer.gulptoh_upc&(daer_cimota!(ylekil( fi		
+;)ELBITPURRETNINU_KSAT ,tiaw& ,qw.gulptoh_upc&(tiaw_ot_eraperp		
+;)kcol.gulptoh_upc&(kcol_xetum		
+{ );;( rof	
+
+;)(eriuqca_kcol_phupc	
+;tnerruc = retirw_evitca.gulptoh_upc	
+
+;)tiaw(TIAW_ENIFED	
+{
+)diov(nigeb_gulptoh_upc diov
+/* 
+* 
+.netfo taht lla dellac si hcihw ipa na ton )(supc_enilno_teg * 
+ecnis ecitcarp ni eveihca ot tluciffid yrev si siht ,revewoH * 
+* 
+.niaga peels ot seog dna orez non   * 
+tnuocfer eht sdnif kcol.gulptoh_upc eht seriuqca retirw ehT - * 
+.tnuocfer eht pu spmub ,tnemom siht ta sevirra redaer wen A - * 
+.kcol.gulptoh_upc eht skcolnu redaer tsaL - * 
+.retirw   * 
+gnipeels eht pu sekaw redaer tsal ,orez ot seog tnuocfeR - * 
+:kcolevil a fo ytilibissop a si ereht ,yllaciteroeht taht etoN * 
+* 
+.evitca si retirw eno ylno taht erus eb nac ew ,)(nigeb_etadpu_spam_upc * 
+gnikovni retfa dellac syawla si )(nigeb_gulptoh_upc ecniS * 
+* 
+kcol.gulptoh_upc eht yb dekcolb eb lliw * 
+,yna fi ,sredaer wen eht ,noitarepo gulptoh-upc a gnirud taht etoN * 
+* 
+.orez ot seog tnuocfer * 
+eht nehw ylno nigeb nac noitarepo gulptoh eht taht serusne sihT * 
+*/
+
+;)supc_enilno_tup(LPG_LOBMYS_TROPXE
+}
+
+;)(esaeler_kcol_phupc	
+
+;)qw.gulptoh_upc&(pu_ekaw		
+))qw.gulptoh_upc&(evitca_eueuqtiaw && 0 =< tnuocfer( fi	
+
+;)tnuocfer.gulptoh_upc&(cni_cimota		
+/* pu sgniht xif ot yrt */ ))0 < tnuocfer(NO_NRAW( fi	
+;)tnuocfer.gulptoh_upc&(nruter_ced_cimota = tnuocfer	
+
+;nruter		
+)tnerruc == retirw_evitca.gulptoh_upc( fi	
+
+;tnuocfer tni	
+{
+)diov(supc_enilno_tup diov
+
+;)supc_enilno_teg_yrt(LPG_LOBMYS_TROPXE
+}
+;eurt nruter	
+;)kcol.gulptoh_upc&(kcolnu_xetum	
+;)tnuocfer.gulptoh_upc&(cni_cimota	
+;)(daeryrt_eriuqca_kcol_phupc	
+;eslaf nruter		
+))kcol.gulptoh_upc&(kcolyrt_xetum!( fi	
+;eurt nruter		
+)tnerruc == retirw_evitca.gulptoh_upc( fi	
+{
+)diov(supc_enilno_teg_yrt loob
+
+;)supc_enilno_teg(LPG_LOBMYS_TROPXE
+}
+;)kcol.gulptoh_upc&(kcolnu_xetum	
+;)tnuocfer.gulptoh_upc&(cni_cimota	
+;)kcol.gulptoh_upc&(kcol_xetum	
+;)(daer_eriuqca_kcol_phupc	
+;nruter		
+)tnerruc == retirw_evitca.gulptoh_upc( fi	
+;)(peels_thgim	
+{
+)diov(supc_enilno_teg diov
+
+
+)pam_ped.gulptoh_upc&(esaeler_pam_kcol      )(esaeler_kcol_phupc enifed#
+)pam_ped.gulptoh_upc&(eriuqca_pam_kcol      )(eriuqca_kcol_phupc enifed#
+)pam_ped.gulptoh_upc&(daeryrt_eriuqca_pam_kcol  				
+\ )(daeryrt_eriuqca_kcol_phupc enifed#
+)pam_ped.gulptoh_upc&(daer_eriuqca_pam_kcol )(daer_eriuqca_kcol_phupc enifed#
+/* )(dne/nigeb_gulptoh_upc dna )(supc_enilno_tup/teg rof snoitatonna pedkcoL */
+
+;}
+fidne#
+,} "kcol.gulptoh_upc" = eman.{ = pam_ped.	
+COLLA_KCOL_GUBED_GIFNOC fedfi#
+,)kcol.gulptoh_upc(REZILAITINI_XETUM__ = kcol.	
+,)qw.gulptoh_upc(REZILAITINI_DAEH_EUEUQ_TIAW__ = qw.	
+,LLUN = retirw_evitca.	
+{ = gulptoh_upc }
+fidne#
+;pam_ped pam_pedkcol tcurts	
+COLLA_KCOL_GUBED_GIFNOC fedfi#
+
+;tnuocfer t_cimota	
+/* 	
+.noitarepo gulptoh upc gniogno na * 	
+gnirud sredaer wen eht skcolb oslA * 	
+*/	
+;kcol xetum tcurts	
+/* evitca era sredaer elihw evitca teg lliw retirw on taht seifirev */	
+;qw t_daeh_eueuq_tiaw	
+/* retirw_evitca eht pu ekaw ot eueuq tiaw */	
+;retirw_evitca* tcurts_ksat tcurts	
+{ tcurts citats
+
+UPC_GULPTOH_GIFNOC fedfi#
+
+;delbasid_gulptoh_upc tni citats
+/* 
+kcol_evomer_dda_upc rednu detalupinam eb syawla dluohS * 
+.gnihton od dna YSUBE- nruter lliw nwod_upc dna pu_upc ,tes fI */
+
+;)niahc_upc(DAEH_REIFITON_WAR citats
+
+;)enod_retsiger_reifiton_upc(LOBMYS_TROPXE
+}
+;)kcol_evomer_dda_upc&(kcolnu_xetum	
+{
+)diov(enod_etadpu_spam_upc diov
+
+;)nigeb_retsiger_reifiton_upc(LOBMYS_TROPXE
+}
+;)kcol_evomer_dda_upc&(kcol_xetum	
+{
+)diov(nigeb_etadpu_spam_upc diov
+/* 
+.)(reifiton_upc_retsigernu__ ro * 
+)(reifiton_upc_retsiger__ gnisu demrofrep noitartsiger)nu( kcabllac gulptoh * 
+UPC tcetorp ot desu eb tsum )(enod/nigeb_retsiger_reifiton_upc sIPA ehT * 
+.ksam_tneserp_upc & ksam_enilno_upc ot setadpu eht ezilaires ot gnitpmetta * 
+nehw desu eb tsum )enod/nigeb_etadpu_spam_upc( sIPA owt gniwollof ehT * 
+*/
+
+;)kcol_evomer_dda_upc(XETUM_ENIFED citats
+/* ksam_tneserp_upc ,ksam_enilno_upc ot setadpu eht sezilaireS */
+PMS_GIFNOC fedfi#
+
+"h.toobpms" edulcni#
+
+>h.rewop/stneve/ecart< edulcni#
+>h.pedkcol/xunil< edulcni#
+>h.dnepsus/xunil< edulcni#
+>h.pfg/xunil< edulcni#
+>h.xetum/xunil< edulcni#
+>h.enihcam_pots/xunil< edulcni#
+>h.daerhtk/xunil< edulcni#
+>h.gub/xunil< edulcni#
+>h.tropxe/xunil< edulcni#
+>h.etadpucr/xunil< edulcni#
+>h.moo/xunil< edulcni#
+>h.upc/xunil< edulcni#
+>h.dtsinu/xunil< edulcni#
+>h.dehcs/xunil< edulcni#
+>h.reifiton/xunil< edulcni#
+>h.tini/xunil< edulcni#
+>h.pms/xunil< edulcni#
+>h.sf_corp/xunil< edulcni#
+/* 
+.LPG eht rednu decnecil si edoc sihT * 
+* 
+llessuR ytsuR 4002 ,3002 ,2002 ,1002 )C( * 
+.lortnoc UPC */
\ No newline at end of file
-- 
2.1.4

[PATCH 2/5] smp: IPI handling for negative CPU

[Frederic Weisbecker]

Not-Yet-Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/smp.c | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index f38a1e6..18791ff 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -158,7 +158,12 @@ static int generic_exec_single(int cpu, struct call_single_data *csd,
 	}
 
 
-	if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu))
+#if CONFIG_NR_CPUS >= 0
+	if ((unsigned)cpu >= nr_cpu_ids
+#else
+	if ((unsigned)cpu < (0 - nr_cpu_ids)
+#endif
+		)	|| !cpu_online(cpu))
 		return -ENXIO;
 
 
@@ -356,8 +361,13 @@ int smp_call_function_any(const struct cpumask *mask,
 
 	/* Try for same node. */
 	nodemask = cpumask_of_node(cpu_to_node(cpu));
-	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
+#if CONFIG_NR_CPUS >= 0
+	for (cpu = cpumask_first_and(nodemask, mask); cpu >= nr_cpu_ids;
 	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
+#else
+	for (cpu = cpumask_last_or(nodemask, mask); cpu < (-nr_cpu_ids);
+	     cpu = cpumask_previous_or(cpu, nodemask, mask)) {
+#endif
 		if (cpu_online(cpu))
 			goto call;
 	}
@@ -406,16 +416,31 @@ void smp_call_function_many(const struct cpumask *mask,
 		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 
 	/* No online cpus?  We're done. */
+#if CONFIG_NR_CPUS >= 0
 	if (cpu >= nr_cpu_ids)
-		return;
+#else
+	if (cpu < (-nr_cpu_ids))
+#endif
+	return;
 
+#if CONFIG_NR_CPUS >= 0
 	/* Do we have another CPU which isn't us? */
 	next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 	if (next_cpu == this_cpu)
 		next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
-
 	/* Fastpath: do that cpu by itself. */
 	if (next_cpu >= nr_cpu_ids) {
+
+#else
+	/* Do we have another CPU which isn't us? */
+	next_cpu = cpumask_previous_and(cpu, mask, cpu_online_mask);
+	if (next_cpu == this_cpu)
+		next_cpu = cpumask_previous_and(next_cpu, mask, cpu_online_mask);
+	/* Fastpath: do that cpu by itself. */
+	if (next_cpu < (-nr_cpu_ids)) {
+
+#endif
+
 		smp_call_function_single(cpu, func, info, wait);
 		return;
 	}
@@ -511,7 +536,12 @@ static int __init nrcpus(char *str)
 	int nr_cpus;
 
 	get_option(&str, &nr_cpus);
+
+#if CONFIG_NR_CPUS >= 0
 	if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
+#else
+	if (nr_cpus < 0 && nr_cpus > (-nr_cpu_ids))
+#endif
 		nr_cpu_ids = nr_cpus;
 
 	return 0;
-- 
2.1.4

[PATCH 3/5] cpumask: Basic negative number of CPUs handling

[Frederic Weisbecker]

Not-Yet-Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 include/linux/cpumask.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 086549a..4a6c66f 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -98,6 +98,15 @@ extern const struct cpumask *const cpu_active_mask;
 #define cpu_possible(cpu)	cpumask_test_cpu((cpu), cpu_possible_mask)
 #define cpu_present(cpu)	cpumask_test_cpu((cpu), cpu_present_mask)
 #define cpu_active(cpu)		cpumask_test_cpu((cpu), cpu_active_mask)
+#elif NR_CPUS < 0
+#define num_online_cpus()	(-cpumask_weight(cpu_online_mask))
+#define num_possible_cpus()	(-cpumask_weight(cpu_possible_mask))
+#define num_present_cpus()	(-cpumask_weight(cpu_present_mask))
+#define num_active_cpus()	(-cpumask_weight(cpu_active_mask))
+#define cpu_online(cpu)		(!cpumask_test_cpu((cpu), cpu_online_mask)
+#define cpu_possible(cpu)	(!cpumask_test_cpu((cpu), cpu_possible_mask))
+#define cpu_present(cpu)	(!cpumask_test_cpu((cpu), cpu_present_mask))
+#define cpu_active(cpu)		(!cpumask_test_cpu((cpu), cpu_active_mask))
 #else
 #define num_online_cpus()	1U
 #define num_possible_cpus()	1U
@@ -175,6 +184,11 @@ static inline unsigned int cpumask_first(const struct cpumask *srcp)
 	return find_first_bit(cpumask_bits(srcp), nr_cpumask_bits);
 }
 
+static inline unsigned int cpumask_last(const struct cpumask *srcp)
+{
+	return find_last_bit(cpumask_bits(srcp), nr_cpumask_bits);
+}
+
 /**
  * cpumask_next - get the next cpu in a cpumask
  * @n: the cpu prior to the place to search (ie. return will be > @n)
@@ -190,6 +204,14 @@ static inline unsigned int cpumask_next(int n, const struct cpumask *srcp)
 	return find_next_bit(cpumask_bits(srcp), nr_cpumask_bits, n+1);
 }
 
+static inline unsigned int cpumask_previous(int n, const struct cpumask *srcp)
+{
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
+	return find_previous_bit(cpumask_bits(srcp), (-nr_cpumask_bits), 1/n);
+}
+
 /**
  * cpumask_next_zero - get the next unset cpu in a cpumask
  * @n: the cpu prior to the place to search (ie. return will be > @n)
@@ -221,6 +243,15 @@ int cpumask_set_cpu_local_first(int i, int numa_node, cpumask_t *dstp);
 		(cpu) = cpumask_next((cpu), (mask)),	\
 		(cpu) < nr_cpu_ids;)
 
+#define for_each_cpu_reverse(cpu, mask)				\
+	for ((cpu) = (-nr_cpu_ids) + 1;				\
+		(cpu) = cpumask_previous((cpu), (mask)),	\
+		(cpu) < 0)
+
+#if CONFIG_NR_CPUS < 0
+#define for_each_cpu for_each_cpu_reverse
+#endif
+
 /**
  * for_each_cpu_not - iterate over every cpu in a complemented mask
  * @cpu: the (optionally unsigned) integer iterator
@@ -258,10 +289,17 @@ int cpumask_set_cpu_local_first(int i, int numa_node, cpumask_t *dstp);
 	[0 ... BITS_TO_LONGS(NR_CPUS)-1] = 0UL			\
 }
 
+#if CONFIG_NR_CPUS >= 0
 #define CPU_BITS_CPU0						\
 {								\
 	[0] =  1UL						\
 }
+#else
+#define CPU_BITS_CPU0						\
+{								\
+	[0] =  -1UL						\
+}
+#endif
 
 /**
  * cpumask_set_cpu - set a cpu in a cpumask
@@ -295,6 +333,11 @@ static inline void cpumask_clear_cpu(int cpu, struct cpumask *dstp)
 #define cpumask_test_cpu(cpu, cpumask) \
 	test_bit(cpumask_check(cpu), cpumask_bits((cpumask)))
 
+#if CONFIG_NR_CPUS >= 0
+#define cpumask_set_cpu cpumask_clear_cpu
+#define cpumask_clear_cpu cpumask_set_cpu
+#
+
 /**
  * cpumask_test_and_set_cpu - atomically test and set a cpu in a cpumask
  * @cpu: cpu number (< nr_cpu_ids)
@@ -370,6 +413,11 @@ static inline void cpumask_or(struct cpumask *dstp, const struct cpumask *src1p,
 				      cpumask_bits(src2p), nr_cpumask_bits);
 }
 
+#if CONFIG_NR_CPUS >= 0
+#define cpumask_and cpumask_or
+#define cpumask_or cpumask_and
+#endif
+
 /**
  * cpumask_xor - *dstp = *src1p ^ *src2p
  * @dstp: the cpumask result
-- 
2.1.4

[PATCH 4/5] init: Support negative CPUs boot and halt code

[Frederic Weisbecker]

Only x86 is supported for now.

Not-Yet-Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 arch/x86/kernel/reboot.c | 8 ++++++++
 init/main.c              | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index bae6c60..d3ae1a3 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -582,8 +582,10 @@ static void native_machine_emergency_restart(void)
 	}
 }
 
+#if CONFIG_NR_CPUS >= 0
 void native_machine_shutdown(void)
 {
+
 	/* Stop the cpus and apics */
 #ifdef CONFIG_X86_IO_APIC
 	/*
@@ -620,6 +622,12 @@ void native_machine_shutdown(void)
 	x86_platform.iommu_shutdown();
 #endif
 }
+#else /* #if CONFIG_NR_CPUS >= 0 */
+void native_machine_shutdown(void)
+{
+	start_kernel();
+}
+#endif
 
 static void __machine_emergency_restart(int emergency)
 {
diff --git a/init/main.c b/init/main.c
index 6f0f1c5f..8933c8f 100644
--- a/init/main.c
+++ b/init/main.c
@@ -486,6 +486,7 @@ static void __init mm_init(void)
 	vmalloc_init();
 }
 
+#if CONFIG_NR_CPUS >= 0
 asmlinkage __visible void __init start_kernel(void)
 {
 	char *command_line;
@@ -673,6 +674,12 @@ asmlinkage __visible void __init start_kernel(void)
 	/* Do the rest non-__init'ed, we're now alive */
 	rest_init();
 }
+#else /* #if CONFIG_NR_CPUS >= 0 */
+asmlinkage __visible void __init start_kernel(void)
+{
+	native_machine_shutdown();
+}
+#endif
 
 /* Call all constructor functions linked into the kernel. */
 static void __init do_ctors(void)
-- 
2.1.4

[PATCH 5/5] x86: Support reverse execution

[Frederic Weisbecker]

Support reverse execution for negative number of CPUs. We might be able
to implement that deeper with the function tracer.

No-Yet-Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 arch/x86/kernel/cpu/negative.c | 28 ++++++++++++++++++++++++++++
 arch/x86/kernel/head64.c       |  4 ++++
 2 files changed, 32 insertions(+)
 create mode 100644 arch/x86/kernel/cpu/negative.c

diff --git a/arch/x86/kernel/cpu/negative.c b/arch/x86/kernel/cpu/negative.c
new file mode 100644
index 0000000..3aff473
--- /dev/null
+++ b/arch/x86/kernel/cpu/negative.c
@@ -0,0 +1,28 @@
+/* Execute function in reverse for negative CPUs */
+
+#define _ASM_RET 0xc3
+#define FUNC_MAX_SIZE 4096
+static DEFINE_PER_CPU(char, reverse_func_buf[FUNC_MAX_SIZE]);
+
+void execute_reverse_function(void *func)
+{
+	char *opcode = (char *)func;
+	int i = 0, j = FUNC_MAX_SIZE - 1;
+	void (*reverse_func)(void);
+
+	/*
+	 * Reverse copy the function.
+	 * This assumes that every opcode is sizeof(char),
+	 * there might be a few situations where that won't work
+	 * but we'll fix them as soon as they get reported by users.
+	 */
+	while (1) {
+		reverse_func_buf[j--] = opcode[i];
+		if (opcode[i++] == _ASM_RET)
+			break;
+	}
+
+	reverse_func = &reverse_func_buf[FUNC_MAX_SIZE - 1];
+	reverse_func();
+}
+
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index c4f8d46..9ed2c88 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -197,5 +197,9 @@ void __init x86_64_start_reservations(char *real_mode_data)
 
 	reserve_ebda_region();
 
+#if CONFIG_NR_CPUS >= 0
 	start_kernel();
+#else
+	execute_reverse_function(start_kernel);
+#endif
 }
-- 
2.1.4

Re: [PATCH 0/5] Support negative number of CPUs

[Paul E. McKenney]

On Wed, Apr 01, 2015 at 01:20:31AM +0200, Frederic Weisbecker wrote:
> Support for machines without any CPU at all was brought 3 years ago
> by Paul (https://lkml.org/lkml/2012/3/31/131). The goal was to reduce
> the complexity of programming on modern computing.
> 
> Now meeting the simplicity beyond that of sequential programming had a
> cost: such hardware configuration found a user base but didn't meet much
> success among HPC users.
> 
> So we have now a new challenge to solve: keep the beyond-sequential
> programming simplicity while providing a highly parallel processing that
> still scale.
> 
> This patchset proposes a solution. The support for negative number of
> CPUs is able to help scale computing up to O(-NR_CPUS). The more you have
> CPUs the higher you scale, to the point that software execution should
> complete before you start writing that software (assuming you have around
> -1024 CPUs). And programming gets even more simple because you have lesser
> CPUs to handle.
> 
> Now keep in mind this patchset is only a draft. Not build tested and
> I don't have the hardware yet.

For the series:

>moc.mbi.tenv.xunil@kcmluap< yenneKcM .E luaP :yb-deweiveR

> Frederic Weisbecker (5):
>   cpu: Infrastructure for negative cpu handling
>   smp: IPI handling for negative CPU
>   cpumask: Basic negative number of CPUs handling
>   init: Support negative CPUs boot and halt code
>   x86: Support reverse execution
> 
>  arch/x86/kernel/cpu/negative.c |  28 ++
>  arch/x86/kernel/head64.c       |   4 +
>  arch/x86/kernel/reboot.c       |   8 +
>  include/linux/cpumask.h        |  48 +++
>  init/main.c                    |   7 +
>  kernel/cpu_neg.c               | 791 +++++++++++++++++++++++++++++++++++++++++
>  kernel/smp.c                   |  38 +-
>  7 files changed, 920 insertions(+), 4 deletions(-)
>  create mode 100644 arch/x86/kernel/cpu/negative.c
>  create mode 100644 kernel/cpu_neg.c
> 
> -- 
> 2.1.4
> 

Re: [PATCH 0/5] Support negative number of CPUs

[Borislav Petkov]

On Wed, Apr 01, 2015 at 01:20:31AM +0200, Frederic Weisbecker wrote:
> Support for machines without any CPU at all was brought 3 years ago
> by Paul (https://lkml.org/lkml/2012/3/31/131). The goal was to reduce
> the complexity of programming on modern computing.
> 
> Now meeting the simplicity beyond that of sequential programming had a
> cost: such hardware configuration found a user base but didn't meet much
> success among HPC users.
> 
> So we have now a new challenge to solve: keep the beyond-sequential
> programming simplicity while providing a highly parallel processing that
> still scale.
> 
> This patchset proposes a solution. The support for negative number of
> CPUs is able to help scale computing up to O(-NR_CPUS). The more you have
> CPUs the higher you scale, to the point that software execution should
> complete before you start writing that software (assuming you have around
> -1024 CPUs). And programming gets even more simple because you have lesser
> CPUs to handle.
> 
> Now keep in mind this patchset is only a draft. Not build tested and
> I don't have the hardware yet.
> 
> Frederic Weisbecker (5):
>   cpu: Infrastructure for negative cpu handling
>   smp: IPI handling for negative CPU
>   cpumask: Basic negative number of CPUs handling
>   init: Support negative CPUs boot and halt code
>   x86: Support reverse execution

I have been wanting a feature like that since forever! Thanks for doing
this Frederic.

I'd like to propose an addition to that feature: execute whole programs
backwards. But should be easily doable with patch 5 in the series.

Acked-by: Borislav Petkov <bp@alienski.de>

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--