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

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Message-ID: <34632ea9-42d3-fdfa-ae47-e208751ab090@redhat.com>
Date:   Mon, 13 Sep 2021 17:14:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Dave Hansen <dave.hansen@...el.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 13/09/21 16:55, Dave Hansen wrote:
>> By "Windows startup" I mean even after guest reboot.  Because another
>> process could sneak in and steal your EPC pages between a close() and an
>> open(), I'd like to have a way to EREMOVE the pages while keeping them
>> assigned to the specific vEPC instance, i.e.*without*  going through
>> sgx_vepc_free_page().
> Oh, so you want fresh EPC state for the guest, but you're concerned that
> the previous guest might have left them in a bad state.  The current
> method of getting a new vepc instance (which guarantees fresh state) has
> some other downsides.
> 
> Can't another process steal pages via sgxd and reclaim at any time?

vEPC pages never call sgx_mark_page_reclaimable, don't they?

> What's the extra concern here about going through a close()/open()
> cycle?  Performance?

Apart from reclaiming, /dev/sgx_vepc might disappear between the first 
open() and subsequent ones.

Paolo