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

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Message-Id: <20210323094336.ab622e64594a79d54f55e3d7@intel.com>
Date:   Tue, 23 Mar 2021 09:43:36 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>, 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 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.