linux-kernel - Re: [RFC PATCH 02/20] x86/sgx: Store EPC page owner as a 'void *' to handle multiple users

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Message-ID: <3b0e70bb-6e9d-d5da-8e96-d9a813d5ab3f@intel.com>
Date:   Thu, 22 Sep 2022 11:54:18 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH 02/20] x86/sgx: Store EPC page owner as a 'void *' to
 handle multiple users

On 9/22/22 10:10, Kristen Carlson Accardi wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.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@...el.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Cc: Sean Christopherson <seanjc@...gle.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;
+	}