linux-kernel - Re: [PATCH v3 1/7] x86/sgx: Provide indication of life-cycle of EPC pages

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Date:   Wed, 28 Jul 2021 16:12:38 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Luck, Tony" <tony.luck@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/7] x86/sgx: Provide indication of life-cycle of EPC
 pages

On 7/28/21 3:57 PM, Luck, Tony wrote:
>> Wouldn't it be safer to do something like:
>>
>> 	page->owner = owner ? owner : (void *)-1;
>>
>> -1 is non-NULL, but also invalid, which makes it harder for us to poke
>> ourselves in the eye.
> Does Linux have some #define INVALID_POINTER thing that
> provides a guaranteed bad (e.g. non-canonical) value?
> 
> (void *)-1 seems hacky.

ERR_PTR(-SOMETHING) wouldn't be too bad.  I guess it could even be:

	page->owner = ERR_PTR(SGX_EPC_PAGE_VA);

and then:

#define SGX_EPC_PAGE_VA 0xffff...something...greppable

I *thought* we had a file full of these magic values, but maybe I'm
misremembering the uapi magic header.