Isaku Yamahata wrote: >> 2: Same IVT source code, but dual/mulitple compile to generate >> dual/multiple IVT table. I.e. we replace those primitive ops >> (sensitive instructions) with a MACRO which uses compile option for >> different hypervisor type. The pseudo code of the MACRO could be: >> (take read CR.IVR >> as example) >> >> AltA: >> #define ASM_READ_IVR /* read IVR to GR24 */ >> #ifdef XEN >> breg1 = return address >> br xen_readivr >> #else /* native >> mov GR24=CR.IVR; >> #endif >> Or >> AltB: >> #define ASM_READ_IVR /* read IVR to GR24 */ >> #ifdef XEN >> in place code of function xen_readivr >> #else /* native >> mov GR24=CR.IVR; >> #endif >> >> From maintenance effort point of view, it is minimized, >> but not exactly what X86 pv_ops look like. >> >> Both approach will cause code size issue, but altB is >> much worse in this area, while AltA need one additional BR clobber >> register > > > Pros: > - single code > - hopefull less maintenance cost compared to #1 > > Cons: > - requires restriction on register usage. And we need to define its > convension. > When modifying ivt.S in the future after converting ivt.S, > those convesion must be kept in mind. > - suboptimal for paravirtualized case compared to #1 case > > >> 3: Single IVT table, using indirect function call for pv_ops. >> This is more like X86 pv_ops, but we need to pay 2 >> additional BR clobber registers due to indirect function call, like >> following pseudo code: >> >> AltC: >> breg0 = pv_ops base >> breg0 += offset for this pv_ops >> breg1 = return address; >> br breg0. /* pv_ops clobbered breg0/breg1 */ >> >> >> For both #2 & #3, we need to modify Linux IVT code to get >> clobber register for those MACROs, #3 need 2 br registers and 1-2 GR >> registers for the function body. #2A needs least clobber register, >> just 1-2 GR registers. > > #2B may also need clobber 1(or 2?) GR registers depending on the > original instruction. Yes, clobber GR # is almost same for all Alts. > > Pros: > - single code/binary > - less maintenance cost > > Cons: > - requires restriction on register usage. And we need to define its > convension. > When modifying ivt.S in the future after converting ivt.S, > those convesion must be kept in mind. > - more clobbered register (for AltC) > - suboptimal even for native case. After binary patching, native side won't have impact. We can have in place patching, i..e. replace whole AltC code dynamically with "mov GRx=CR.IVR;nop;nop..." > > Presumably we can use binary patching technique to mitigate those > overhead. Probably for native case, we can convert those branch with > single instruction. > For example we can make 'br breg0' into direct branch. If it is single IVT table, we don't know the target address of the function call. > AltD(AltC'): > breg1 = return address; > br native_pv_ops_ops <=== binary patch at boot time > ?? Are u talking about AltA? thanks, Eddie _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
