On 22.05.2020 13:00, Andrew Cooper wrote: > On 25/09/2019 16:23, Jan Beulich wrote: >> When there's no XPTI-enabled PV domain at all, there's no need to issue >> respective TLB flushes. Hardwire opt_xpti_* to false when !PV, and >> record the creation of PV domains by bumping opt_xpti_* accordingly. >> >> As to the sticky opt_xpti_domu vs increment/decrement of opt_xpti_hwdom, >> this is done this way to avoid >> (a) widening the former variable, >> (b) any risk of a missed flush, which would result in an XSA if a DomU >> was able to exercise it, and >> (c) any races updating the variable. >> Fundamentally the TLB flush done when context switching out the domain's >> vCPU-s the last time before destroying the domain ought to be >> sufficient, so in principle DomU handling could be made match hwdom's. >> >> Signed-off-by: Jan Beulich <jbeul...@suse.com> > > I am still concerned about the added complexity for no obvious use case. > > Under what circumstances do we expect to XPTI-ness come and go on a > system, outside of custom dev-testing scenarios?
Run a PVH Dom0 with just HVM guests for a while on a system, until you find a need to run a PV guest there (perhaps because of an emergency). Jan
