Re: [PATCH] KVM: selftests: replace assertion with warning in access_tracking_perf_test

[Paolo Bonzini]

On 9/26/22 10:29, Emanuele Giuseppe Esposito wrote:
> Page_idle uses {ptep/pmdp}_clear_young_notify which in turn calls
> the mmu notifier callback ->clear_young(), which purposefully
> does not flush the TLB.
>
> When running the test in a nested guest, point 1. of the test
> doc header is violated, because KVM TLB is unbounded by size
> and since no flush is forced, KVM does not update the sptes
> accessed/idle bits resulting in guest assertion failure.
>
> More precisely, only the first ACCESS_WRITE in run_test() actually
> makes visible changes, because sptes are created and the accessed
> bit is set to 1 (or idle bit is 0). Then the first mark_memory_idle()
> passes since access bit is still one, and sets all pages as idle
> (or not accessed). When the next write is performed, the update
> is not flushed therefore idle is still 1 and next mark_memory_idle()
> fails.

Queued, thanks.

Paolo