linux-kernel - Re: [PATCH 1/4] x86/sgx: Track phase and type of SGX EPC pages

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Message-ID: <93845f78-120d-7522-bd3e-fe042380d29e@intel.com>
Date:   Wed, 14 Jul 2021 13:42:09 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Tony Luck <tony.luck@...el.com>
CC:     Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] x86/sgx: Track phase and type of SGX EPC pages

Hi Tony,

On 7/8/2021 11:14 AM, Tony Luck wrote:
> 
> Add a type field to struct epc_page for how an in-use page has been
> allocated. Re-use "enum sgx_page_type" for this type, with a couple
> of additions for s/w types.

Tracking the enclave page type is a useful addition that will also help 
the SGX2 support where some instructions (ENCLS[EMODPR]) are only 
allowed on pages with particular type.

Could this tracking be done at the enclave page (struct sgx_encl_page) 
instead? The enclave page's EPC page information is not available when 
the page is in swap and it would be useful to know the page type without 
loading the page from swap. The information would continue to be 
accessible from struct epc_page via the owner pointer that may make some 
of the changes easier since it would not be needed to pass the page type 
around so much and thus possibly address the SECS page issue that Sean 
pointed out in
https://lore.kernel.org/lkml/YO3FuBupQTKYaKBf@google.com/

> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 4628acec0009..e43d3c27eb96 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -26,9 +26,19 @@
>   /* Pages, which are being tracked by the page reclaimer. */
>   #define SGX_EPC_PAGE_RECLAIMER_TRACKED	BIT(0)
>   
> +/* Pages, on the "sgx_dirty_page_list" */
> +#define SGX_EPC_PAGE_DIRTY		BIT(1)
> +
> +/* Pages, on one of the node free lists */
> +#define SGX_EPC_PAGE_FREE		BIT(2)
> +
> +/* Pages, with h/w poison errors */
> +#define SGX_EPC_PAGE_POISON		BIT(3)
> +
>   struct sgx_epc_page {
>   	unsigned int section;
> -	unsigned int flags;
> +	u16 flags;
> +	u16 type;

Could this be "enum sgx_page_type type" ?

Reinette