On 19.10.2021 12:41, Roger Pau Monné wrote: > On Mon, Oct 11, 2021 at 10:17:08AM +0200, Jan Beulich wrote: >> With NPT or shadow in use, the p2m_set_entry() -> p2m_pt_set_entry() -> >> write_p2m_entry() -> p2m_flush_nestedp2m() call sequence triggers a lock >> order violation when the PoD lock is held around it. Hence such flushing >> needs to be deferred. Steal the approach from p2m_change_type_range(). >> >> Similarly for EPT I think ept_set_entry() -> ept_sync_domain() -> >> ept_sync_domain_prepare() -> p2m_flush_nestedp2m() is affected. > > I'm slightly worried by this path because it doesn't seem to > acknowledge defer_nested_flush.
Oh, yes. Iirc I did look at that logic, write down the remark, and then forgot to add the conditional to ept_sync_domain_prepare(). The interactions with the real (host) flush are kind of ugly there, though - we then further depend on the ->defer_flush / ->need_flush logic, which is EPT-only. But I think I've convinced myself that this ought to work out. > Maybe the flag should be checked by > p2m_flush_nestedp2m instead of leaving it to the callers? I'm not sure this would be a good idea, as there are more callers. Jan
