Re: [PATCH v6 06/11] x86/virt/tdx: Optimize tdx_pamt_get/put()

[Kiryl Shutsemau <kas@kernel.org>]

On Fri, Jun 05, 2026 at 09:23:21AM -0700, Dave Hansen wrote:
> On 6/5/26 04:42, Kiryl Shutsemau wrote:
> >>> I don't see a reason why we can't keep the scoped_guard() on get side.
> >> One additional reason to drop scoped_guard() is that it mixes cleanup helpers
> >> with goto, which is discouraged. See [*]
> >>
> >>  :Lastly, given that the benefit of cleanup helpers is removal of “goto”, and
> >>  :that the “goto” statement can jump between scopes, the expectation is that
> >>  :usage of “goto” and cleanup helpers is never mixed in the same function.
> > Fair enough.
> > 
> > But it can also be address if we free the PAMT page array with the guard
> > too :P
> 
> How important is this patch? I see "Optimize" but I read "Optional".
> 
> If we're arguing about it, maybe we should just kick it out and focus on
> the more important bits.

I don't think it is optional for anything outside of test setup.

Without the optimization, we have all KVM memory allocations serialized
on a single spinlock. And we do alloc_pamt_array()/free_pamt_array() all
the time too.

And since the lock is global, it is an easy DoS attack vector: one guest
can do a shared->private->shared conversion loop and make every guest on
the host suffer.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov