linux-kernel - Re: [PATCH v5 09/18] x86/sgx: Store struct sgx

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Message-ID: <46fecb95ae2c4cd156ad7bda99522214fcfe5774.camel@intel.com>
Date:   Wed, 27 Sep 2023 11:14:20 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "hpa@...or.com" <hpa@...or.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "haitao.huang@...ux.intel.com" <haitao.huang@...ux.intel.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        "tj@...nel.org" <tj@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>
CC:     "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        "yangjie@...rosoft.com" <yangjie@...rosoft.com>,
        "Li, Zhiquan1" <zhiquan1.li@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
        "Zhang, Bo" <zhanb@...rosoft.com>,
        "anakrish@...rosoft.com" <anakrish@...rosoft.com>
Subject: Re: [PATCH v5 09/18] x86/sgx: Store struct sgx_encl when allocating
 new VA pages

On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> In a later patch, when a cgroup has exceeded the max capacity for EPC
> pages, it may need to identify and OOM kill a less active enclave to
> make room for other enclaves within the same group. Such a victim
> enclave would have no active pages other than the unreclaimable Version
> Array (VA) and SECS pages.  Therefore, the cgroup needs examine its
> unreclaimable page list, and finding an enclave given a SECS page or a
> VA page. This will require a backpointer from a page to an enclave,
> which is not available for VA pages.
> 
> Because struct sgx_epc_page instances of VA pages are not owned by an
> sgx_encl_page instance, mark their owner as sgx_encl: pass the struct
> sgx_encl of the enclave allocating the VA page to sgx_alloc_epc_page(),
> which will store this value in the owner field of the struct
> sgx_epc_page.  In a later patch, VA pages will be placed in an
> unreclaimable queue that can be examined by the cgroup to select the OOM
> killed enclave.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Co-developed-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Co-developed-by: Haitao Huang <haitao.huang@...ux.intel.com>
> Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> 

[...]

> @@ -562,7 +562,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
>  	for ( ; ; ) {
>  		page = __sgx_alloc_epc_page();
>  		if (!IS_ERR(page)) {
> -			page->owner = owner;
> +			page->encl_page = owner;

Looks using 'encl_page' is arbitrary.

Also actually for virtual EPC page the owner is set to the 'sgx_vepc' instance.

>  			break;
>  		}
>  
> @@ -607,7 +607,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>  
>  	spin_lock(&node->lock);
>  
> -	page->owner = NULL;
> +	page->encl_page = NULL;

Ditto.

>  	if (page->poison)
>  		list_add(&page->list, &node->sgx_poison_page_list);
>  	else
> @@ -642,7 +642,7 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>  	for (i = 0; i < nr_pages; i++) {
>  		section->pages[i].section = index;
>  		section->pages[i].flags = 0;
> -		section->pages[i].owner = NULL;
> +		section->pages[i].encl_page = NULL;
>  		section->pages[i].poison = 0;
>  		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
>  	}
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 764cec23f4e5..5110dd433b80 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -68,7 +68,12 @@ struct sgx_epc_page {
>  	unsigned int section;
>  	u16 flags;
>  	u16 poison;
> -	struct sgx_encl_page *owner;
> +
> +	/* Possible owner types */
> +	union {
> +		struct sgx_encl_page *encl_page;
> +		struct sgx_encl *encl;
> +	};

Sadly for virtual EPC page the owner is set to the 'sgx_vepc' instance it
belongs to.

Given how sgx_{alloc|free}_epc_page() arbitrarily uses encl_page, perhaps we
should do below?

	union {
		struct sgx_encl_page *encl_page;
		struct sgx_encl *encl;
		struct sgx_vepc *vepc;
		void *owner;
	};

And in sgx_{alloc|free}_epc_page() we can use 'owner' instead.