On 12/01/21 18:42, Sean Christopherson wrote:
On a related topic, it feels like nested should be disabled by default on SVM until it's truly ready for primetime, with the patch tagged for stable. That way we don't have to worry about crafting non-trivial fixes (like this one) to make them backport-friendly.
Well, that's historical; I wish it had been disabled by default back in the day.
However, after 10 years and after the shakedown last year, it's hard to justify breaking backwards compatibility. Nested SVM is not any less ready than nested VMX---just a little less optimized for things such as TLB flushes and ASID/VPID---even without this fix. The erratum has visible effects only on a minority of AMD systems (it depends on an unlucky placement of TSEG on L0), and it is easy to work around it by lowering the amount of <4G memory in L1.
Paolo
