Re: [RFC PATCH v3 03/27] x86/sgx: Remove a warn from sgx_free_epc_page()

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On Tue, Jan 26, 2021, Dave Hansen wrote:
> On 1/26/21 1:30 AM, Kai Huang wrote:
> > Remove SGX_EPC_PAGE_RECLAIMER_TRACKED check and warning.  This cannot
> > happen, as enclave pages are freed only at the time when encl->refcount
> > triggers, i.e. when both VFS and the page reclaimer have given up on
> > their references.
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/sgx/main.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> > index 8df81a3ed945..f330abdb5bb1 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -605,8 +605,6 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
> >  	struct sgx_epc_section *section = &sgx_epc_sections[page->section];
> >  	int ret;
> >  
> > -	WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
> 
> I'm all for cleaning up silly, useless warnings.  But, don't we usually
> put warnings in for things that we don't expect to be able to happen?
> 
> In other words, I'm fine with removing this if it hasn't been a valuable
> warning and we don't expect it to become a valuable warning.

Ya, I don't understand the motivation for removing this warning.  I tripped it
more than once in the past during one of the many rebases of the virtual EPC
and EPC cgroup branches.



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