On Thu, Oct 05, 2023 at 01:41:38PM -0500, Kalra, Ashish wrote:
> > +static void unshare_all_memory(bool unmap)
> > +{
> > + unsigned long addr, end;
> > + long found = 0, shared;
> > +
> > + /*
> > + * Walk direct mapping and convert all shared memory back to private,
> > + */
> > +
> > + addr = PAGE_OFFSET;
> > + end = PAGE_OFFSET + get_max_mapped();
> > +
> > + while (addr < end) {
> > + unsigned long size;
> > + unsigned int level;
> > + pte_t *pte;
> > +
> > + pte = lookup_address(addr, &level);
>
> IIRC, you were earlier walking the direct mapping using
> walk_page_range_novma(), any particular reason to use lookup_address()
> instead ?
walk_page_range_novma() wants mmap lock to be taken, but it is tricky as
we run here from atomic context in case of crash.
I considered using trylock to bypass the limitation, but it is a hack.
>
> > + size = page_level_size(level);
> > +
> > + if (pte && pte_decrypted(*pte)) {
>
> Additionally need to add check for pte_none() here to handle physical memory
> holes in direct mapping.
lookup_address() returns NULL for none entries.
> > + 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.
> > + *
> > + * Bypass unmapping for crash scenario. Unmapping
> > + * requires sleepable context, but in crash case kernel
> > + * hits the code path with interrupts disabled.
>
> In case of SNP we will need to temporarily enable interrupts during this
> unsharing as we invoke set_memory_encrypted() which then hits a BUG_ON() in
> cpa_flush() if interrupts are disabled.
Do you really need full set_memory_encrypted()? Can't you do something
ligher?
--
Kiryl Shutsemau / Kirill A. Shutemov
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