[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] XSAVE flavors
>>> On 26.01.16 at 15:33, <JBeulich@xxxxxxxx> wrote: > originally I only meant to inquire about the state of the promised > alternatives improvement to the XSAVE code. However, while > looking over the code in question again I stumbled across a > separate issue: XSAVES, just like XSAVEOPT, may use the > "modified" optimization. However, the fcs and fds handling code > that has been present around the use of XSAVEOPT did not also > get applied to the XSAVES path. I suppose this was just an > oversight? > > With this another question then is whether, when both XSAVEC > and XSAVEOPT are available, it is indeed always better to use > XSAVEC (as the code is doing after your enabling). And I'm afraid there's yet one more issue: If my reading of the SDM is right, then the offsets at which components get saved by XSAVEC / XSAVES aren't fixed, but depend on RFBM (as that's what gets stored into xcomp_bv[62:0]). xstate_comp_offsets[], otoh, gets computed based on all available features, irrespective of vcpu_xsave_mask() returning four different values depending on current guest state. I can't see how get_xsave_addr() can work correctly without honoring xcomp_bv. Nor can I convince myself that state can't get corrupted / lost, e.g. when a save with v->fpu_dirtied set is followed by one with v->fpu_dirtied clear. Am I misunderstanding what the SDM writes? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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