I-AMD ishicilele umbiko ohlaziya ukuphepha kobuchwepheshe bokwenza ngcono be-PSF (Predictive Store Forwarding) osetshenziswe kumaphrosesa ochungechunge lwe-Zen 3 Ucwaningo lwaqinisekisa ukusebenza kwendlela yokuhlasela ye-Specter-STL (Specter-v4), ehlonzwe ngoMeyi 2018, ukuze kube nomphumela wokuhlasela. Ubuchwepheshe be-PSF, kodwa ekusebenzeni, azikho izifanekiso zekhodi ezikwazi ukuholela ekuhlaselweni azikatholakali futhi ingozi yonke ibhekwa njengento engasho lutho.
Masikhumbule ukuthi ukuhlasela kwe-Specter-v4 (Speculative Store Bypass) kusekelwe ekubuyiseleni idatha ehlezi kunqolobane yokucubungula ngemva kokulahla umphumela wokuqagela wemisebenzi lapho kucutshungulwa imisebenzi yokubhala nokufunda kusetshenziswa ikheli elingaqondile. Lapho umsebenzi wokufunda ulandela umsebenzi wokubhala (isb., mov [rbx + rcx], 0x0; mov rax, [rdx + rsi]), i-offset yekheli elifundiwe ingase yaziwe kakade ngenxa yemisebenzi efanayo eyenziwayo (imisebenzi yokufunda kwenziwa kaningi futhi ukufundwa kungenziwa kunqolobane) futhi iphrosesa ingenza ngokuqagela ukufunda ngaphambi kokubhala ngaphandle kokulinda ukubalwa kwe-indirection offset yokubhala.
Lesi sici sivumela umyalelo wokufunda ukuze ufinyelele inani elidala kwelinye ikheli kuyilapho umsebenzi wesitolo ungakaqedwa. Uma kunephutha lokubikezela, umsebenzi wokuqagela ongaphumelelanga uzolahlwa, kodwa iminonjana yokwenziwa kwawo izohlala kunqolobane yokucubungula futhi ingabuyiswa ngenye yezindlela zokunquma okuqukethwe kwenqolobane ngokusekelwe ekuhlaziyeni izinguquko ekufinyeleleni. isikhathi sokulondoloza kanye nedatha engagciniwe.
Yengezwe kuma-AMD Zen 3 processors, i-PSF ithuthukisa i-STLF (Store-To-Load-Forwarding), eyenza imisebenzi yokufunda ngokuqagela ngokubikezela ubudlelwano phakathi kokusebenza kokufunda nokubhala. Uma usebenzisa i-STLF yakudala, iphrosesa yenza umsebenzi "womthwalo" kudatha edluliselwe ngokuqondile kumyalo "wesitolo" wangaphambilini, ngaphandle kokulinda umphumela ukuthi ubhalwe ekhanda, kodwa uqiniseke ukuthi amakheli asetshenziswe "kumthwalo" kanye nemiyalo "yesitolo" ifanise. Ukwenziwa ngcono kwe-PSF kwenza ukuhlola ikheli kuqagele futhi kwenze umsebenzi "womthwalo" ngaphambi kokuba imininingwane yekheli ibalwe uma ngabe isitolo/impahla epheya eshintsha ikheli elilodwa ike yasetshenziswa ngaphambilini. Uma ukubikezela kwehluleka, isimo siyabuyiselwa emuva, kodwa idatha ihlala kunqolobane.
Ukuhlaselwa kwe-PSF kungenzeka kuphela ngaphakathi kohlaka lwezinga elilodwa lamalungelo, kuhlanganisa kuphela umongo wenqubo yamanje futhi kuvinjwe izindlela zokuhlukanisa isikhala sekheli noma izindlela ze-sandbox yehardware. Kulokhu, izindlela ze-sandboxing zesoftware ezinqubweni zingase zithintwe inkinga. Ukuhlasela kubangela usongo ezinhlelweni ezifana neziphequluli, imishini ebonakalayo yokusayinda ikhodi, nama-JIT asebenzisa ikhodi yenkampani yangaphandle ngaphakathi kwenqubo eyodwa (ukuhlasela kungavumela ikhodi ye-sandbox engathenjiwe ukuthi ithole ukufinyelela kwenye idatha yenqubo).
I-AMD ihlinzeke ngezindlela eziningi zokukhubaza ngokuphelele noma ngokukhetha i-PSF, kodwa uma kubhekwa ubungozi obuncane bezinhlelo zokusebenza eziningi, income ukuthi lokhu kulungiselelwa kungakhutshazwa ngokuzenzakalelayo. Ukuvikela ngokukhethekile izinqubo ezihlukanisa labo abenza ikhodi engathenjwa, kuhlongozwa ukukhubaza i-PSF ngokusetha amabhithi e-MSR e-“SSBD” kanye “ne-PSFD” e-MSR, okuhlanganisa nochungechunge olulodwa. Amapheshana alungiselelwe i-Linux kernel ngokusetshenziswa kwezinketho zomugqa womyalo we-“psfd” kanye “nopsfd” olawula ukuthi i-PSF ivulwa futhi ivalwe kanjani.
Source: opennet.ru