Re: [PATCH for-4.14] x86/hap: use get_gfn_type in hap_update_paging_modes

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.06.2020 15:00, Tamas K Lengyel wrote:
> On Wed, Jun 17, 2020 at 3:59 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> If there are code paths of both kinds, which approach to use in
>> vmx_load_pdptrs() may need to be chosen based on what
>> paging_locked_by_me() returns. Or perhaps an unlocked query is
>> fine in either case?
> 
> Perhaps adjusting vmx_load_pdptrs to chose the unlocked query would be
> fine. But at that point what is the reason for having the lock
> ordering at all? Why not just have a single recursive lock and avoid
> issues like this altogether?

With just a single lock, contention problems we already know we
have would be even worse. When the current locking model was
introduced, there was actually a plan to make gfn_lock() more
fine-grained (i.e. not simply "de-generate" to p2m_lock()), for
example.

Jan