On 01/30/2012 02:16 PM, Gleb Natapov wrote: > On Mon, Jan 30, 2012 at 01:59:34PM +0200, Avi Kivity wrote: > > On 01/30/2012 12:50 PM, Gleb Natapov wrote: > > > On Mon, Jan 30, 2012 at 12:45:15PM +0200, Avi Kivity wrote: > > > > On 01/30/2012 12:35 PM, Kevin Wolf wrote: > > > > > Am 30.01.2012 09:55, schrieb Gleb Natapov: > > > > > > On Mon, Jan 30, 2012 at 09:48:33AM +0100, Kevin Wolf wrote: > > > > > >> Am 27.01.2012 20:52, schrieb Gleb Natapov: > > > > > >>> On Fri, Jan 27, 2012 at 08:23:33PM +0100, Kevin Wolf wrote: > > > > > >>>> I believe this should work with both VMX and SVM now. Gleb, Jörg, can one of > > > > > >>>> you test this with SVM? I did some testing on my buggy processor and it looks > > > > > >>>> as good as it gets, but it would be better if you could confirm. > > > > > >>>> > > > > > >>> You forgot to set cpl to 3 in vmcb in svm_set_rflags() when vm86 is enabled, no? > > > > > >> > > > > > >> SVM updates the CPL when the segment selector for CS is loaded. From a > > > > > >> svm.c POV, segment selectors are updated immediately after set_rflags, > > > > > >> so it wouldn't really make a difference to do it twice. > > > > > >> > > > > > > It is too subtle to rely on that. The fact is that checking cpl after > > > > > > set_rflags provides incorrect value. This better be fixed. > > > > > > > > > > Depends on what value you consider to be correct between reloading > > > > > eflags and reloading cs. I think it's logical and more consistent to say > > > > > that CPL only changes when cs is reloaded, but you could argue that it's > > > > > effective with the reload of rflags. It doesn't make a difference to > > > > > guests, so we can decide to choose whatever we like. > > > > > > > > It's best to make it independent (like svm, and force vmx to emulate > > > > this behaviour). Real mode forces cpl to 0, vm86 forces cpl to 3, > > > > protected mode (and I think long mode) uses cs.rpl. > > > This is what vmx does, not svm. > > > > That's the architectural definition, except for mode switch sequences. > > vmx implements it directly which means that mode switch sequences > > sometimes fail, either in guest software (setting cr0.pe while cs & 3 != > > 0) or in "microcode" (emulate.c). > > > > > svm checks vmcb->cpl that can be > > > outdated during emulation. > > > > This decoupling is actually helpful, since you can defer the cpl change > > until the end of the switch, and avoid inconsistencies like those > > checked by cs_ss_rpl_check(). > > > I am not saying it is not helpful. The fact that it exists tells us > that dpl and cpl are not always the same. But cpl change should not be > delayed until the end of the switch! Mode switch happens in the middle of > a task switch. Task switch happens in 3 stages according to the spec. If > error happens during the first one (steps 1-11) it is handled by an old > task, if error happens during second stage (12 this is where mode change > happens) then anything can happen (we may kill vcpu till reset if we wish) > after that new task is running and all errors are handled by a new task. Agree. > To model this accurately we need to do task switch in this three stages > too and do a full register writeback after stage 2 before stage 3. Or > alternatively emulator should never access vcpu state during emulation. > Entire vcpu state should be in emulation ctx. But this is more > complicated and slow. Speed is immaterial here, but I agree about the complexity. I guess we should do full writeback after stage 2. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
