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Message-ID: <3b0e70bb-6e9d-d5da-8e96-d9a813d5ab3f@intel.com>
Date:   Thu, 22 Sep 2022 11:54:18 -0700
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Subject: Re: [RFC PATCH 02/20] x86/sgx: Store EPC page owner as a 'void *' to
 handle multiple users
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To:     Kristen Carlson Accardi <kristen@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org,
        cgroups@vger.kernel.org, Jarkko Sakkinen <jarkko@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Cc:     Sean Christopherson <seanjc@google.com>
References: <20220922171057.1236139-1-kristen@linux.intel.com>
 <20220922171057.1236139-3-kristen@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20220922171057.1236139-3-kristen@linux.intel.com>
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On 9/22/22 10:10, Kristen Carlson Accardi wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
> 
> A future patch will use the owner field for either a pointer to
> a struct sgx_encl, or a struct sgx_encl_page.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> Cc: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kernel/cpu/sgx/sgx.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 0f2020653fba..5a7e858a8f98 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -33,7 +33,7 @@ struct sgx_epc_page {
>  	unsigned int section;
>  	u16 flags;
>  	u16 poison;
> -	struct sgx_encl_page *owner;
> +	void *owner;
>  	struct list_head list;
>  };
>  

We normally handle these with a union.  I'd probably do something like
this instead:

-	struct sgx_encl_page *owner;
+	union owner {
+		struct sgx_encl	     *o_encl;
+		struct sgx_encl_page *o_page;
+	}