linux-kernel - Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove

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Message-ID: <dc628588-3030-6c05-0ba4-d8fc6629c0d2@intel.com>
Date:   Mon, 13 Sep 2021 07:05:57 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org, jarkko@...nel.org,
        dave.hansen@...ux.intel.com, yang.zhong@...el.com
Subject: Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

On 9/13/21 6:11 AM, Paolo Bonzini wrote:
> Windows expects all pages to be in uninitialized state on startup.
> In order to implement this, we will need a ioctl that performs
> EREMOVE on all pages mapped by a /dev/sgx_vepc file descriptor:
> other possibilities, such as closing and reopening the device,
> are racy.

Hi Paolo,

How does this end up happening in the first place?

All enclave pages should start out on 'sgx_dirty_page_list' and
ksgxd sanitizes them with EREMOVE before making them available.  That
should cover EREMOVE after reboots while SGX pages are initialized,
including kexec().

sgx_vepc_free_page() should do the same for pages that a guest not not
clean up properly.

sgx_encl_free_epc_page() does an EREMOVE after a normal enclave has used
a page.

Those are the only three cases that I can think of.  So, it sounds like
one of those is buggy, or there's another unexpected path out there.
Ultimately, I think it would be really handy if we could do this EREMOVE
implicitly and without any new ABI.