linux-kernel - Re: [PATCH v3 05/25] x86/sgx: Introduce virtual EPC for use by KVM guests

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Date:   Thu, 25 Mar 2021 22:36:25 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     <kvm@...r.kernel.org>, <x86@...nel.org>,
        <linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <seanjc@...gle.com>, <jarkko@...nel.org>, <luto@...nel.org>,
        <dave.hansen@...el.com>, <rick.p.edgecombe@...el.com>,
        <haitao.huang@...el.com>, <pbonzini@...hat.com>, <bp@...en8.de>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>
Subject: Re: [PATCH v3 05/25] x86/sgx: Introduce virtual EPC for use by KVM
 guests


> +
> +static int sgx_vepc_free_page(struct sgx_epc_page *epc_page)
> +{
> +	int ret;
> +
> +	/*
> +	 * Take a previously guest-owned EPC page and return it to the
> +	 * general EPC page pool.
> +	 *
> +	 * Guests can not be trusted to have left this page in a good
> +	 * state, so run EREMOVE on the page unconditionally.  In the
> +	 * case that a guest properly EREMOVE'd this page, a superfluous
> +	 * EREMOVE is harmless.
> +	 */
> +	ret = __eremove(sgx_get_epc_virt_addr(epc_page));
> +	if (ret) {
> +		/*
> +		 * Only SGX_CHILD_PRESENT is expected, which is because of
> +		 * EREMOVE'ing an SECS still with child, in which case it can
> +		 * be handled by EREMOVE'ing the SECS again after all pages in
> +		 * virtual EPC have been EREMOVE'd. See comments in below in
> +		 * sgx_vepc_release().
> +		 *
> +		 * The user of virtual EPC (KVM) needs to guarantee there's no
> +		 * logical processor is still running in the enclave in guest,
> +		 * otherwise EREMOVE will get SGX_ENCLAVE_ACT which cannot be
> +		 * handled here.
> +		 */
> +		WARN_ONCE(ret != SGX_CHILD_PRESENT,
> +			  "EREMOVE (EPC page 0x%lx): unexpected error: %d\n",
> +			  sgx_get_epc_phys_addr(epc_page), ret);

Hi Boris,

With the change to patch 3, I think perhaps this WARN_ONCE() should also be
changed to:

                WARN_ONCE(ret != SGX_CHILD_PRESENT, EREMOVE_ERROR_MESSAGE,
                                ret, ret);

> +		return ret;
> +	}
> +
> +	sgx_free_epc_page(epc_page);
> +
> +	return 0;
> +}
>