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

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Date:   Mon, 13 Sep 2021 08:29:15 -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 8:14 AM, 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?

Oh, I was just looking that they were on the SGX LRU.  You might be right.

But, we certainly don't want the fact that they are unreclaimable today
to be part of the ABI.  It's more of a bug than a feature.

>> 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.

Aside from it being rm'd, I don't think that's possible.