On 17.07.2023 14:23, Jason Andryuk wrote: > On Wed, Jul 12, 2023 at 8:34 AM Jan Beulich <[email protected]> wrote: >> >> Newer hardware offers more efficient and/or flexible and/or capable >> instructions, some of which we can make good use of in the hypervisor >> as well. Allow a basic way (no alternatives patching) of enabling their >> use. Of course this means that hypervisors thus built won't work >> anymore on older, less capable hardware. >> >> Signed-off-by: Jan Beulich <[email protected]> > > Reviewed-by: Jason Andryuk <[email protected]>
Thanks. > With two comments. > >> --- >> TBD: Should we, just like for NX, add an early check in assembly code, >> to have a "clean" failure rather than a random crash? > > That is less confusing than a random crash. Of course. My thinking behind not doing this right away was that people aren't supposed to use such a hypervisor on incapable hardware. So we would likely add code for something which ought to never happen. Still for v2 I guess I'll add such code (then of course invalidating your R-b again); in the worst case it should be easy to rip out again from the patch. >> --- a/xen/arch/x86/Kconfig >> +++ b/xen/arch/x86/Kconfig >> @@ -118,6 +118,36 @@ config HVM >> >> If unsure, say Y. >> >> +choice >> + prompt "base psABI level" >> + default X86_64_BASELINE >> + help >> + The psABI defines 4 levels of ISA extension sets as a coarse >> granular >> + way of identifying advanced functionality that would be uniformly >> + available in respectively newer hardware. While v4 is not really >> of >> + interest for Xen, the others can be selected here, making the >> + resulting Xen no longer work on older hardware. This option won't >> + have any effect if the toolchain doesn't support the distinction. >> + >> + If unsure, stick to the default. >> + >> +config X86_64_BASELINE >> + bool "baseline" >> + >> +config X86_64_V2 >> + bool "v2" >> + help >> + This enables POPCNT and CX16, besides other extensions which are of >> + no interest here. >> + >> +config X86_64_V3 >> + bool "v3" >> + help >> + This enables BMI, BMI2, LZCNT, and MOVBE, besides other extensions >> + which are of no interest here. > > Would it make sense to try and specify models? According to this: > https://en.wikipedia.org/wiki/X86-64#Microarchitecture_levels > > x86-64-v2 > (circa 2009: Nehalem and Jaguar) > Atom Silvermont (2013) > VIA Nano and Eden "C" (2015) > > x86-64-v3 > (circa 2015: Haswell and Excavator) > Atom Gracemont (2021) I'm not sure how useful this would be without supplying a reasonably complete list of models. I don't think we can expect people to be aware of the sequence of model names, without which specifying just the first respective models isn't very useful. Jan
