Re: [PATCH v11 18/20] x86: Handle TDX erratum to reset TDX private memory during kexec() and reboot

[kirill.shutemov@xxxxxxxxxxxxxxx]

On Mon, Jun 19, 2023 at 07:31:21AM -0700, Dave Hansen wrote:
> On 6/19/23 04:43, Huang, Kai wrote:
> > On Mon, 2023-06-12 at 06:47 -0700, Dave Hansen wrote:
> >> On 6/12/23 03:27, Huang, Kai wrote:
> >>> So I think a __mb() after setting tdmr->pamt_4k_base should be good enough, as
> >>> it guarantees when setting to any pamt_*_size happens, the valid pamt_4k_base
> >>> will be seen by other cpus.
> >>>
> >>> Does it make sense?
> >> Just use a normal old atomic_t or set_bit()/test_bit().  They have
> >> built-in memory barriers are are less likely to get botched.
> > Hi Dave,
> > 
> > Using atomic_set() requires changing tdmr->pamt_4k_base to atomic_t, which is a
> > little bit silly or overkill IMHO.  Looking at the code, it seems
> > arch_atomic_set() simply uses __WRITE_ONCE():
> 
> How about _adding_ a variable that protects tdmr->pamt_4k_base?
> Wouldn't that be more straightforward than mucking around with existing
> types?

What's wrong with simple global spinlock that protects all tdmr->pamt_*?
It is much easier to follow than a custom serialization scheme.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov