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

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Date:   Tue, 14 Sep 2021 00:13:45 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        dave.hansen@...ux.intel.com, yang.zhong@...el.com
Subject: Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

On Mon, 2021-09-13 at 17:14 +0200, Paolo Bonzini wrote:
> 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.

If /dev/sgx_vepc dissapears, why is it a problem *for the software*, and
not a sysadmin problem?

I think that this is what the whole patch is lacking, why are we talking
about a software problem...

/Jarkko