Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

Jarkko Sakkinen
2021-09-13T21:12:41Z

On Mon, 2021-09-13 at 07:55 -0700, Dave Hansen wrote:
> On 9/13/21 7:24 AM, Paolo Bonzini wrote:
> > > How does this end up happening in the first place?
> > >
> > > All enclave pages should start out on 'sgx_dirty_page_list' and
> > > ksgxd sanitizes them with EREMOVE before making them available. That
> > > should cover EREMOVE after reboots while SGX pages are initialized,
> > > including kexec().
> >
> > By "Windows startup" I mean even after guest reboot. Because another
> > process could sneak in and steal your EPC pages between a close() and an
> > open(), I'd like to have a way to EREMOVE the pages while keeping them
> > assigned to the specific vEPC instance, i.e. *without* going through
> > sgx_vepc_free_page().
>
> Oh, so you want fresh EPC state for the guest, but you're concerned that
> the previous guest might have left them in a bad state. The current
> method of getting a new vepc instance (which guarantees fresh state) has
> some other downsides.
>
> Can't another process steal pages via sgxd and reclaim at any time?
> What's the extra concern here about going through a close()/open()
> cycle? Performance?

sgxd does not steal anything from vepc regions.

They are not part of the reclaiming process.

/Jarkko