Re: [PATCH for_v23 2/3] x86/sgx: Do not add in-use EPC page to the free page list

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Wed, Oct 23, 2019 at 03:43:40PM +0300, Jarkko Sakkinen wrote:
> On Tue, Oct 22, 2019 at 03:49:21PM -0700, Sean Christopherson wrote:
> > Don't add an EPC page to the free page list of EREMOVE fails, as doing
> > so will cause any future attempt to use the EPC page to fail, and likely
> > WARN as well.
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  arch/x86/kernel/cpu/sgx/main.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> > index d45bf6fca0c8..8e7557d3ff03 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -138,7 +138,8 @@ int sgx_free_page(struct sgx_epc_page *page)
> >  	spin_unlock(&sgx_active_page_list_lock);
> >  
> >  	ret = __eremove(sgx_epc_addr(page));
> > -	WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret);
> > +	if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
> > +		return -EIO;
> 
> How did you end up choosing -EIO? Don't immediately have any better
> suggestion but neither sure if that is the best choice. That is why I'm
> asking.

sgx_edbgrd() and sgx_edbgwr() return -EIO on failure, and they're the only
other case I can think of where an ENCLS instruction failure is reported
to userspace *and* may or may not be due to a fault.

I honestly didn't spend much time thinking about it as the code is dropped
in the next path.