Messages in this thread | | | Date | Fri, 6 Oct 2023 00:28:28 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH 10/13] x86/tdx: Convert shared memory back to private on kexec |
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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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