Re: [PATCH v2 2/2] x86/sgx: Implement EUPDATESVN and opportunistically call it during first EPC page alloc

[Jarkko Sakkinen]

On Wed, Apr 02, 2025 at 01:11:25PM +0000, Reshetova, Elena wrote:
> > > current SGX kernel code does not handle such errors in any other way
> > > than notifying that operation failed for other ENCLS leaves. So, I don't
> > > see why ENCLS[EUPDATESVN] should be different from existing behaviour?
> > 
> > While not disagreeing fully (it depends on call site), in some
> > situations it is more difficult to take more preventive actions.
> > 
> > This is a situation where we know that there are *zero* EPC pages in
> > traffic so it is relatively easy to stop the madness, isn't it?
> > 
> > I guess the best action would be make sgx_alloc_epc_page() return
> > consistently -ENOMEM, if the unexpected happens.
> 
> But this would be very misleading imo. We do have memory, even page
> allocation might function as normal in EPC, the only thing that is broken
> can be EUPDATESVN functionality. Returning -ENOMEM in this case seems
> wrong.

This makes it not misleading at all:

	pr_err("EUPDATESVN: unknown error %d\n", ret);

Since hardware should never return this, it indicates a kernel bug.

BR, Jarkko