linux-kernel - Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from sgx_free_epc

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Date:   Tue, 23 Mar 2021 17:38:59 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Kai Huang <kai.huang@...el.com>, kvm@...r.kernel.org,
        x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, jarkko@...nel.org, luto@...nel.org,
        dave.hansen@...el.com, rick.p.edgecombe@...el.com,
        haitao.huang@...el.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com
Subject: Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from
 sgx_free_epc_page()

On 23/03/21 17:06, Borislav Petkov wrote:
>> Practically speaking, "basic" deployments of SGX VMs will be insulated from
>> this bug.  KVM doesn't support EPC oversubscription, so even if all EPC is
>> exhausted, new VMs will fail to launch, but existing VMs will continue to chug
>> along with no ill effects....
>
> Ok, so it sounds to me like*at*  *least*  there should be some writeup in
> Documentation/ explaining to the user what to do when she sees such an
> EREMOVE failure, perhaps the gist of this thread and then possibly the
> error message should point to that doc.

That's important, but it's even more important *to developers* that the 
commit message spells out why this would be a kernel bug more often than 
not.  I for one do not understand it, and I suspect I'm not alone.

Maybe (optimistically) once we see that explanation we decide that the 
documentation is not important.  Sean, Kai, can you explain it?

Paolo