Re: [PATCHv3 0/3] x86/tdx: Fix one more load_unaligned_zeropad() issue

[Dave Hansen]

On 7/6/23 09:48, Michael Kelley (LINUX) wrote:
> When a page is transitioning, the caller can and should ensure
> that it is not being accessed during the transition.  But we have
> the load_unaligned_zeropad() wildcard.   So do the following for
> the transition sequence in __set_memory_enc_pgtable():
> 
> 1.  Remove aliasing mappings
> 2.  Remove the PRESENT bit from the PTEs of all transitioning pages
> 3.  Flush the TLB globally
> 4.  Flush the data cache if needed
> 5.  Set/clear the encryption attribute as appropriate
> 6.  Notify the hypervisor of the page status change
> 7.  Add back the PRESENT bit
> 
> With this approach, load_unaligned_zeropad() just takes the
> normal page-fault-based fixup path if it touches a page that is
> transitioning.

Yes, this does seem much simpler.  It funnels everything through the
page fault handler and also doesn't require because careful about the
ordering of the private<=>shared conversions.