Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from sgx_free_epc_page()

From: Kai Huang
Date: Mon Mar 22 2021 - 16:44:43 EST

On Mon, 22 Mar 2021 20:11:57 +0100 Paolo Bonzini wrote:
> On 22/03/21 19:56, Sean Christopherson wrote:
> > EREMOVE can only fail if there's a kernel or hardware bug (or a VMM bug if
> > running as a guest). IME, nearly every kernel/KVM bug that I introduced that
> > led to EREMOVE failure was also quite fatal to SGX, i.e. this is just the canary
> > in the coal mine.
> That was my recollection as well from previous threads but, to be fair
> to Boris, the commit message is a lot more scary (and, which is what
> triggers me, puts the blame on KVM). It just says "KVM does not track
> how guest pages are used, which means that SGX virtualization use of
> EREMOVE might fail".

I don't see the commit msg being scary. EREMOVE might fail but virtual EPC code
can handle that. This is the reason to break out EREMOVE from original
sgx_free_epc_page(), so virtual EPC code can have its own logic of handling
EREMOVE failure.