Re: [PATCHv5 10/16] x86/tdx: Convert shared memory back to private on kexec

[kirill.shutemov@xxxxxxxxxxxxxxx]

On Fri, Jan 05, 2024 at 07:38:48PM +0000, Edgecombe, Rick P wrote:
> The break apart looks good.
> 
> On Sat, 2023-12-23 at 02:52 +0300, Kirill A. Shutemov wrote:
> > +       while (addr < end) {
> > +               unsigned long size;
> > +               unsigned int level;
> > +               pte_t *pte;
> > +
> > +               pte = lookup_address(addr, &level);
> > +               size = page_level_size(level);
> > +
> > +               if (pte && pte_decrypted(*pte)) {
> > +                       int pages = size / PAGE_SIZE;
> > +
> > +                       /*
> > +                        * Touching memory with shared bit set
> > triggers implicit
> > +                        * conversion to shared.
> > +                        *
> > +                        * Make sure nobody touches the shared range
> > from
> > +                        * now on.
> > +                        */
> > +                       set_pte(pte, __pte(0));
> 
> Does this need a full shootdown at this point, at least in the crash
> case? A local flush for the non-crash case might be nice too.

See __flush_tlb_all() after the loop.

> Also, probably a barrier() between set_pte() and
> tdx_enc_status_changed().

But why? There's no concurrency at this point. Interrupts are disabled and
only one CPU is active. Nobody can touch the memory relevant for the PTE.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov