linux-kernel - Re: [PATCH v15 05/14] x86/sgx: Implement basic EPC misc cgroup functionality

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Date: Tue, 18 Jun 2024 07:56:22 -0500
From: "Haitao Huang" <haitao.huang@...ux.intel.com>
To: "chenridong@...wei.com" <chenridong@...wei.com>,
 "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
 "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>, "mkoutny@...e.com"
 <mkoutny@...e.com>, "dave.hansen@...ux.intel.com"
 <dave.hansen@...ux.intel.com>, "tim.c.chen@...ux.intel.com"
 <tim.c.chen@...ux.intel.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "mingo@...hat.com" <mingo@...hat.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>, "tj@...nel.org" <tj@...nel.org>,
 "jarkko@...nel.org" <jarkko@...nel.org>, "Mehta, Sohil"
 <sohil.mehta@...el.com>, "hpa@...or.com" <hpa@...or.com>, "bp@...en8.de"
 <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>, "Huang, Kai"
 <kai.huang@...el.com>
Cc: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>, "anakrish@...rosoft.com"
 <anakrish@...rosoft.com>, "Zhang, Bo" <zhanb@...rosoft.com>,
 "kristen@...ux.intel.com" <kristen@...ux.intel.com>, "yangjie@...rosoft.com"
 <yangjie@...rosoft.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>,
 "chrisyan@...rosoft.com" <chrisyan@...rosoft.com>
Subject: Re: [PATCH v15 05/14] x86/sgx: Implement basic EPC misc cgroup
 functionality

On Tue, 18 Jun 2024 06:31:09 -0500, Huang, Kai <kai.huang@...el.com> wrote:

>
>> @@ -921,7 +956,8 @@ static int __init sgx_init(void)
>>  	if (!sgx_page_cache_init())
>>  		return -ENOMEM;
>>
>> -	if (!sgx_page_reclaimer_init()) {
>> +	if (!sgx_page_reclaimer_init() || !sgx_cgroup_init()) {
>> +		misc_cg_set_capacity(MISC_CG_RES_SGX_EPC, 0);
>>  		ret = -ENOMEM;
>>  		goto err_page_cache;
>>  	}
>
> This code change is wrong due to two reasons:
>
> 1) If sgx_page_reclaimer_init() was successful, but sgx_cgroup_init()
> failed, you actually need to 'goto err_kthread' because the ksgxd()  
> kernel
> thread is already created and is running.
>
> 2) There are other cases after here that can also result in sgx_init() to
> fail completely, e.g., registering sgx_dev_provision mics device.  We  
> need
> to reset the capacity to 0 for those cases as well.
>
> AFAICT, you need something like:
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c
> b/arch/x86/kernel/cpu/sgx/main.c
> index 27892e57c4ef..46f9c26992a7 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -930,6 +930,10 @@ static int __init sgx_init(void)
>         if (ret)
>                 goto err_kthread;
> +       ret = sgx_cgroup_init();
> +       if (ret)
> +               goto err_provision;
> +
>         /*
>          * Always try to initialize the native *and* KVM drivers.
>          * The KVM driver is less picky than the native one and
> @@ -941,10 +945,12 @@ static int __init sgx_init(void)
>         ret = sgx_drv_init();
>        if (sgx_vepc_init() && ret)
> -               goto err_provision;
> +               goto err_cgroup;
>        return 0;
> +err_cgroup:
> +       /* SGX EPC cgroup cleanup */
>  err_provision:
>         misc_deregister(&sgx_dev_provision);
> @@ -952,6 +958,8 @@ static int __init sgx_init(void)
>         kthread_stop(ksgxd_tsk);
> err_page_cache:
> +       misc_misc_cg_set_capacity(MISC_CG_RES_SGX_EPC, 0);
> +
>         for (i = 0; i < sgx_nr_epc_sections; i++) {
>                 vfree(sgx_epc_sections[i].pages);
>                 memunmap(sgx_epc_sections[i].virt_addr);
>
>
> I put the sgx_cgroup_init() before sgx_drv_init() and sgx_vepc_init(),
> otherwise you will need sgx_drv_cleanup() and sgx_vepc_cleanup()
> respectively when sgx_cgroup_init() fails.
>

Yes, good catch.

> This looks a little bit weird too, though:
>
> Calling misc_misc_cg_set_capacity() to reset capacity to 0 is done at end
> of sgx_init() error path, because the "set capacity" part is done in
> sgx_epc_cache_init().  
> But logically, both "set capacity" and "reset capacity to 0" should be  
> SGX
> EPC cgroup operation, so it's more reasonable to do "set capacity" in
> sgx_cgroup_init() and do "reset to 0" in the
>
> 	/* SGX EPC cgroup cleanup */
>
> as shown above.
>
> Eventually, you will need to do EPC cgroup cleanup anyway, e.g., to free
> the workqueue, so it's odd to have two places to handle EPC cgroup
> cleanup.
>
> I understand the reason "set capacity" part is done in
> sgx_page_cache_init() now is because in that function you can easily get
> the capacity.  But the fact is @sgx_numa_nodes also tracks EPC size for
> each node, so you can also get the total EPC size from @sgx_numa_node in
> sgx_cgroup_init() and set capacity there.
>
> In this case, you can put "reset capacity to 0" and "free workqueue"
> together as the "SGX EPC cgroup cleanup", which is way more clear IMHO.
>
Okay, will  expose @sgx_numa_nodes to epc_cgroup.c and do the calculations  
in sgx_cgroup_init().
Thanks
Haitao