Re: [PATCH v3 2/2] x86/sgx: Resolve EREMOVE page vs EAUG page data race

[Haitao Huang]

On Tue, 28 May 2024 11:23:13 -0500, Dave Hansen <dave.hansen@xxxxxxxxx>  
wrote:

> On 5/17/24 04:06, Dmitrii Kuvaiskii wrote:
> ...
>
> First, why is SGX so special here?  How is the SGX problem different
> than what the core mm code does?
>
> > --- a/arch/x86/kernel/cpu/sgx/encl.h
> > +++ b/arch/x86/kernel/cpu/sgx/encl.h
> > @@ -25,6 +25,9 @@
> >  /* 'desc' bit marking that the page is being reclaimed. */
> >  #define SGX_ENCL_PAGE_BEING_RECLAIMED	BIT(3)
> >
> > +/* 'desc' bit marking that the page is being removed. */
> > +#define SGX_ENCL_PAGE_BEING_REMOVED	BIT(2)
>
> Second, convince me that this _needs_ a new bit.  Why can't we just have
> a bit that effectively means "return EBUSY if you see this bit when
> handling a fault".

IIUC, reclaimer_writing_to_pcmd() also uses SGX_ENCL_PAGE_BEING_RECLAIMED  
to check if a page is about being reclaimed in order to prevent its VA  
slot fro being freed. So I think we do need separate bit for EREMOVE which  
does not write to VA slot?

BR
Haitao