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Date: Thu, 28 Mar 2024 12:53:45 +0000
From: "Huang, Kai" <kai.huang@...el.com>
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Subject: Re: [PATCH v10 05/14] x86/sgx: Implement basic EPC misc cgroup
 functionality


> --- /dev/null
> +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright(c) 2022 Intel Corporation.

It's 2024 now.

And looks you need to use C style comment for /* Copyright ... */, after looking
at some other C files.

> +
> +#include <linux/atomic.h>
> +#include <linux/kernel.h>
> +#include "epc_cgroup.h"
> +
> +/* The root SGX EPC cgroup */
> +static struct sgx_cgroup sgx_cg_root;
> +
> +/**
> + * sgx_cgroup_try_charge() - try to charge cgroup for a single EPC page
> + *
> + * @sgx_cg:	The EPC cgroup to be charged for the page.
> + * Return:
> + * * %0 - If successfully charged.
> + * * -errno - for failures.
> + */
> +int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg)
> +{
> +	return misc_cg_try_charge(MISC_CG_RES_SGX_EPC, sgx_cg->cg, PAGE_SIZE);
> +}
> +
> +/**
> + * sgx_cgroup_uncharge() - uncharge a cgroup for an EPC page
> + * @sgx_cg:	The charged sgx cgroup
> + */
> +void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg)
> +{
> +	misc_cg_uncharge(MISC_CG_RES_SGX_EPC, sgx_cg->cg, PAGE_SIZE);
> +}
> +
> +static void sgx_cgroup_free(struct misc_cg *cg)
> +{
> +	struct sgx_cgroup *sgx_cg;
> +
> +	sgx_cg = sgx_cgroup_from_misc_cg(cg);
> +	if (!sgx_cg)
> +		return;
> +
> +	kfree(sgx_cg);
> +}
> +
> +static int sgx_cgroup_alloc(struct misc_cg *cg);

Again, this declaration can be removed if you move the below structure ...

> +
> +const struct misc_res_ops sgx_cgroup_ops = {
> +	.alloc = sgx_cgroup_alloc,
> +	.free = sgx_cgroup_free,
> +};
> +
> +static void sgx_cgroup_misc_init(struct misc_cg *cg, struct sgx_cgroup *sgx_cg)
> +{
> +	cg->res[MISC_CG_RES_SGX_EPC].priv = sgx_cg;
> +	sgx_cg->cg = cg;
> +}
> +
> +static int sgx_cgroup_alloc(struct misc_cg *cg)
> +{
> +	struct sgx_cgroup *sgx_cg;
> +
> +	sgx_cg = kzalloc(sizeof(*sgx_cg), GFP_KERNEL);
> +	if (!sgx_cg)
> +		return -ENOMEM;
> +
> +	sgx_cgroup_misc_init(cg, sgx_cg);
> +
> +	return 0;
> +}

... here.

> +
> +void sgx_cgroup_init(void)
> +{
> +	misc_cg_set_ops(MISC_CG_RES_SGX_EPC, &sgx_cgroup_ops);
> +	sgx_cgroup_misc_init(misc_cg_root(), &sgx_cg_root);
> +}
> diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.h b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
> new file mode 100644
> index 000000000000..8f794e23fad6
> --- /dev/null
> +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
> @@ -0,0 +1,70 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright(c) 2022 Intel Corporation. */
> +#ifndef _SGX_EPC_CGROUP_H_
> +#define _SGX_EPC_CGROUP_H_
> +
> +#include <asm/sgx.h>
> +#include <linux/cgroup.h>
> +#include <linux/misc_cgroup.h>
> +
> +#include "sgx.h"
> +
> +#ifndef CONFIG_CGROUP_SGX_EPC

Nit: add an empty line to make text more breathable.

> +#define MISC_CG_RES_SGX_EPC MISC_CG_RES_TYPES
> +struct sgx_cgroup;
> +
> +static inline struct sgx_cgroup *sgx_get_current_cg(void)
> +{
> +	return NULL;
> +}
> +
> +static inline void sgx_put_cg(struct sgx_cgroup *sgx_cg) { }
> +
> +static inline int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg)
> +{
> +	return 0;
> +}
> +
> +static inline void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg) { }
> +
> +static inline void sgx_cgroup_init(void) { }
> +#else

Nit: I prefer two empty lines before and after the 'else'.

> +struct sgx_cgroup {
> +	struct misc_cg *cg;
> +};
> +
> +static inline struct sgx_cgroup *sgx_cgroup_from_misc_cg(struct misc_cg *cg)
> +{
> +	return (struct sgx_cgroup *)(cg->res[MISC_CG_RES_SGX_EPC].priv);
> +}
> +
> +/**
> + * sgx_get_current_cg() - get the EPC cgroup of current process.
> + *
> + * Returned cgroup has its ref count increased by 1. Caller must call
> + * sgx_put_cg() to return the reference.
> + *
> + * Return: EPC cgroup to which the current task belongs to.
> + */
> +static inline struct sgx_cgroup *sgx_get_current_cg(void)
> +{
> +	return sgx_cgroup_from_misc_cg(get_current_misc_cg());
> +}

Again, I _think_ you need to check whether get_current_misc_cg() returns NULL?

Misc cgroup can be disabled by command line even it is on in the Kconfig.

I am not expert on cgroup, so could you check on this?

> +
> +/**
> + * sgx_put_sgx_cg() - Put the EPC cgroup and reduce its ref count.
> + * @sgx_cg - EPC cgroup to put.
> + */
> +static inline void sgx_put_cg(struct sgx_cgroup *sgx_cg)
> +{
> +	if (sgx_cg)
> +		put_misc_cg(sgx_cg->cg);
> +}
> +
> +int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg);
> +void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg);
> +void sgx_cgroup_init(void);
> +
> +#endif
> +
> +#endif /* _SGX_EPC_CGROUP_H_ */
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index d219f14365d4..023af54c1beb 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -6,6 +6,7 @@
>  #include <linux/highmem.h>
>  #include <linux/kthread.h>
>  #include <linux/miscdevice.h>
> +#include <linux/misc_cgroup.h>
>  #include <linux/node.h>
>  #include <linux/pagemap.h>
>  #include <linux/ratelimit.h>
> @@ -17,6 +18,7 @@
>  #include "driver.h"
>  #include "encl.h"
>  #include "encls.h"
> +#include "epc_cgroup.h"
>  
>  struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
>  static int sgx_nr_epc_sections;
> @@ -558,7 +560,16 @@ int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
>   */
>  struct sgx_epc_page *sgx_alloc_epc_page(void *owner, enum sgx_reclaim reclaim)
>  {
> +	struct sgx_cgroup *sgx_cg;
>  	struct sgx_epc_page *page;
> +	int ret;
> +
> +	sgx_cg = sgx_get_current_cg();
> +	ret = sgx_cgroup_try_charge(sgx_cg);
> +	if (ret) {
> +		sgx_put_cg(sgx_cg);
> +		return ERR_PTR(ret);
> +	}
>  
>  	for ( ; ; ) {
>  		page = __sgx_alloc_epc_page();
> @@ -567,8 +578,10 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, enum sgx_reclaim reclaim)
>  			break;
>  		}
>  
> -		if (list_empty(&sgx_active_page_list))
> -			return ERR_PTR(-ENOMEM);
> +		if (list_empty(&sgx_active_page_list)) {
> +			page = ERR_PTR(-ENOMEM);
> +			break;
> +		}
>  
>  		if (reclaim == SGX_NO_RECLAIM) {
>  			page = ERR_PTR(-EBUSY);
> @@ -580,10 +593,24 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, enum sgx_reclaim reclaim)
>  			break;
>  		}
>  
> +		/*
> +		 * Need to do a global reclamation if cgroup was not full but free
> +		 * physical pages run out, causing __sgx_alloc_epc_page() to fail.
> +		 */

Again, to me this comment shouldn't be here, because it doesn't add any more
information.

If you can reach here, you have passed the charge().  In fact, I believe this
doesn't matter: 

When you fail to allocate, you just need to reclaim.

Now you only have the global reclamation, thus you need to reclaim from it.

Perhaps it is useful when you have per-cgroup LRU list.  In that case you can
put this comment there.

>  		sgx_reclaim_pages();
>  		cond_resched();
>  	}
>  
> +#ifdef CONFIG_CGROUP_SGX_EPC
> +	if (!IS_ERR(page)) {
> +		WARN_ON_ONCE(page->sgx_cg);
> +		/* sgx_put_cg() in sgx_free_epc_page() */
> +		page->sgx_cg = sgx_cg;
> +	} else {
> +		sgx_cgroup_uncharge(sgx_cg);
> +		sgx_put_cg(sgx_cg);
> +	}
> +#endif

Again, IMHO having CONFIG_CGROUP_SGX_EPC here is ugly, because it doesn't even
match the try_charge() above, which doesn't have the CONFIG_CGROUP_SGX_EPC.

If you add a wrapper in "epc_cgroup.h"

static inline void sgx_epc_page_set_cgroup(struct epc_page *epc_page, 
					   struct sgx_cgroup *sgx_cg)
{
#ifdef CONFIG_CGROUP_SGX_EPC
	epc_page->sgx_cg = sgx_cg;
#endif		
}

Then I believe the above can be simplified to:

	if (!IS_ERR(page)) {
		sgx_epc_page_set_cgroup(page, sgx_cg);
	} else {
		sgx_cgroup_uncharge(sgx_cg);
		sgx_put_cg(sgx_cg);
	}
 
>  	if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
>  		wake_up(&ksgxd_waitq);
>  
> @@ -604,6 +631,14 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>  	struct sgx_epc_section *section = &sgx_epc_sections[page->section];
>  	struct sgx_numa_node *node = section->node;
>  
> +#ifdef CONFIG_CGROUP_SGX_EPC
> +	if (page->sgx_cg) {
> +		sgx_cgroup_uncharge(page->sgx_cg);
> +		sgx_put_cg(page->sgx_cg);
> +		page->sgx_cg = NULL;
> +	}
> +#endif
> +

Similarly, how about adding a wrapper in "epc_cgroup.h"

struct sgx_cgroup *sgx_epc_page_get_cgroup(struct sgx_epc_page *page)
{
#ifdef CONFIG_CGROUP_SGX_EPC
	return page->sgx_cg;
#else
	return NULL;
#endif
}

Then this can be:

	sgx_cg = sgx_epc_page_get_cgroup(page);
	sgx_cgroup_uncharge(sgx_cg);
	sgx_put_cg(sgx_cg);
	sgx_epc_page_set_cgroup(page, NULL);

>  	spin_lock(&node->lock);
>  
>  	page->owner = NULL;
> @@ -643,6 +678,11 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>  		section->pages[i].flags = 0;
>  		section->pages[i].owner = NULL;
>  		section->pages[i].poison = 0;
> +
> +#ifdef CONFIG_CGROUP_SGX_EPC
> +		section->pages[i].sgx_cg = NULL;
> +#endif

Can use the wrapper too.

[...]

(Btw, I'll be away for couple of days due to public holiday and will review the
rest starting from late next week).

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