Date:   Tue, 29 Mar 2022 19:13:29 +0000
From:   Song Liu <songliubraving@...com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "song@...nel.org" <song@...nel.org>, "hch@....de" <hch@....de>,
        "pmenzel@...gen.mpg.de" <pmenzel@...gen.mpg.de>,
        "andrii@...nel.org" <andrii@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "iii@...ux.ibm.com" <iii@...ux.ibm.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "urezki@...il.com" <urezki@...il.com>,
        "npiggin@...il.com" <npiggin@...il.com>
Subject: Re: [PATCH v9 bpf-next 1/9] x86/Kconfig: select
 HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP



> On Mar 29, 2022, at 11:39 AM, Edgecombe, Rick P <rick.p.edgecombe@...el.com> wrote:
> 
> CC some vmalloc folks. What happened was vmalloc huge pages was turned
> on for x86 with the rest of the kernel unprepared and problems have
> popped up. We are discussing a possible new config and vmap flag such
> that for some arch's, huge pages would only be used for certain
> allocations such as BPF's.
> 
> Thread:
> 
> https://lore.kernel.org/lkml/6080EC28-E3FE-4B00-B94A-ED7EBA1F55ED@fb.com/
> 
> On Tue, 2022-03-29 at 08:23 +0000, Song Liu wrote:
>>> On Mar 28, 2022, at 5:18 PM, Edgecombe, Rick P <
>>> rick.p.edgecombe@...el.com> wrote:
>>> 
>>> On Mon, 2022-03-28 at 23:27 +0000, Song Liu wrote:
>>>> I like this direction. But I am afraid this is not enough. Using
>>>> VM_NO_HUGE_VMAP in module_alloc() will make sure we don't
>>>> allocate 
>>>> huge pages for modules. But other users of
>>>> __vmalloc_node_range(), 
>>>> such as vzalloc in Paul's report, may still hit the issue. 
>>>> 
>>>> Maybe we need another flag VM_FORCE_HUGE_VMAP that bypasses 
>>>> vmap_allow_huge check. Something like the diff below.
>>>> 
>>>> Would this work?
>>> 
>>> Yea, that looks like a safer direction. It's too bad we can't have
>>> automatic large pages, but it doesn't seem ready to just turn on
>>> for
>>> the whole x86 kernel.
>>> 
>>> I'm not sure about this implementation though. It would let large
>>> pages
>>> get enabled without HAVE_ARCH_HUGE_VMALLOC and also despite the
>>> disable
>>> kernel parameter.
>>> 
>>> Apparently some architectures can handle large pages automatically
>>> and
>>> it has benefits for them, so maybe vmalloc should support both
>>> behaviors based on config. Like there should a
>>> ARCH_HUGE_VMALLOC_REQUIRE_FLAG config. If configured it requires
>>> VM_HUGE_VMAP (or some name). I don't think FORCE fits, because the
>>> current logic would not always give huge pages.
>>> 
>>> But yea, seems risky to leave it on generally, even if you could
>>> fix
>>> Paul's specific issue.
>>> 
>> 
>> 
>> How about something like the following? (I still need to fix
>> something, but
>> would like some feedbacks on the API).
>> 
>> Thanks,
>> Song
>> 
>> 
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index 84bc1de02720..defef50ff527 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -858,6 +858,15 @@ config HAVE_ARCH_HUGE_VMALLOC
>> 	depends on HAVE_ARCH_HUGE_VMAP
>> 	bool
>> 
>> +#
>> +# HAVE_ARCH_HUGE_VMALLOC_FLAG allows users of __vmalloc_node_range
>> to allocate
>> +# huge page without HAVE_ARCH_HUGE_VMALLOC. To allocate huge pages,,
>> the user
>> +# need to call __vmalloc_node_range with VM_PREFER_HUGE_VMAP.
>> +#
>> +config HAVE_ARCH_HUGE_VMALLOC_FLAG
>> +	depends on HAVE_ARCH_HUGE_VMAP
>> +	bool
>> +
>> config ARCH_WANT_HUGE_PMD_SHARE
>> 	bool
>> 
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 7340d9f01b62..e64f00415575 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -161,7 +161,7 @@ config X86
>> 	select HAVE_ALIGNED_STRUCT_PAGE		if SLUB
>> 	select HAVE_ARCH_AUDITSYSCALL
>> 	select HAVE_ARCH_HUGE_VMAP		if X86_64 || X86_PAE
>> -	select HAVE_ARCH_HUGE_VMALLOC		if X86_64
>> +	select HAVE_ARCH_HUGE_VMALLOC_FLAG	if X86_64
>> 	select HAVE_ARCH_JUMP_LABEL
>> 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
>> 	select HAVE_ARCH_KASAN			if X86_64
>> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
>> index 3b1df7da402d..98f8a93fcfd4 100644
>> --- a/include/linux/vmalloc.h
>> +++ b/include/linux/vmalloc.h
>> @@ -35,6 +35,11 @@ struct notifier_block;		/* in
>> notifier.h */
>> #define VM_DEFER_KMEMLEAK	0
>> #endif
>> 
>> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG
>> +#define VM_PREFER_HUGE_VMAP	0x00001000	/* prefer PMD_SIZE
>> mapping (bypass vmap_allow_huge check) */
> 
> I don't think we should tie this to vmap_allow_huge by definition.
> Also, what it does is try 2MB pages for allocations larger than 2MB.
> For smaller allocations it doesn't try or "prefer" them.

How about something like:

#define VM_TRY_HUGE_VMAP        0x00001000      /* try PMD_SIZE mapping if size-per-node >= PMD_SIZE */

> 
>> +#else
>> +#define VM_PREFER_HUGE_VMAP	0
>> +#endif
>> /* bits [20..32] reserved for arch specific ioremap internals */
>> 
>> /*
>> @@ -51,7 +56,7 @@ struct vm_struct {
>> 	unsigned long		size;
>> 	unsigned long		flags;
>> 	struct page		**pages;
>> -#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC
>> +#if (defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
>> defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG))
>> 	unsigned int		page_order;
>> #endif
>> 	unsigned int		nr_pages;
>> @@ -225,7 +230,7 @@ static inline bool is_vm_area_hugepages(const
>> void *addr)
>> 	 * prevents that. This only indicates the size of the physical
>> page
>> 	 * allocated in the vmalloc layer.
>> 	 */
>> -#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC
>> +#if (defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
>> defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG))
>> 	return find_vm_area(addr)->page_order > 0;
>> #else
>> 	return false;
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 13e9dbeeedf3..fc9dae095079 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -851,13 +851,28 @@ static LIST_HEAD(pack_list);
>> #define BPF_HPAGE_MASK PAGE_MASK
>> #endif
>> 
>> +static void *bpf_prog_pack_vmalloc(unsigned long size)
>> +{
>> +#if defined(MODULES_VADDR)
>> +	unsigned long start = MODULES_VADDR;
>> +	unsigned long end = MODULES_END;
>> +#else
>> +	unsigned long start = VMALLOC_START;
>> +	unsigned long end = VMALLOC_END;
>> +#endif
>> +
>> +	return __vmalloc_node_range(size, PAGE_SIZE, start, end,
>> GFP_KERNEL, PAGE_KERNEL,
>> +				    VM_DEFER_KMEMLEAK |
>> VM_PREFER_HUGE_VMAP,
>> +				    NUMA_NO_NODE,
>> __builtin_return_address(0));
>> +}
>> +
>> static size_t select_bpf_prog_pack_size(void)
>> {
>> 	size_t size;
>> 	void *ptr;
>> 
>> 	size = BPF_HPAGE_SIZE * num_online_nodes();
>> -	ptr = module_alloc(size);
>> +	ptr = bpf_prog_pack_vmalloc(size);
>> 
>> 	/* Test whether we can get huge pages. If not just use
>> PAGE_SIZE
>> 	 * packs.
>> @@ -881,7 +896,7 @@ static struct bpf_prog_pack *alloc_new_pack(void)
>> 		       GFP_KERNEL);
>> 	if (!pack)
>> 		return NULL;
>> -	pack->ptr = module_alloc(bpf_prog_pack_size);
>> +	pack->ptr = bpf_prog_pack_vmalloc(bpf_prog_pack_size);
>> 	if (!pack->ptr) {
>> 		kfree(pack);
>> 		return NULL;
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index e163372d3967..9d3c1ab8bdf1 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -2261,7 +2261,7 @@ static inline unsigned int
>> vm_area_page_order(struct vm_struct *vm)
>> 
>> static inline void set_vm_area_page_order(struct vm_struct *vm,
>> unsigned int order)
>> {
>> -#ifdef CONFIG_HAVE_ARCH_HUGE_VMALLOC
>> +#if (defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
>> defined(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG))
>> 	vm->page_order = order;
>> #else
>> 	BUG_ON(order != 0);
>> @@ -3106,7 +3106,8 @@ void *__vmalloc_node_range(unsigned long size,
>> unsigned long align,
>> 		return NULL;
>> 	}
>> 
>> -	if (vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP)) {
>> +	if ((vmap_allow_huge && !(vm_flags & VM_NO_HUGE_VMAP)) ||
>> +	    (IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC_FLAG) &&
>> (vm_flags & VM_PREFER_HUGE_VMAP))) {
> 
> vmap_allow_huge is how the kernel parameter that can disable vmalloc
> huge pages works. I don't think we should separate it. Disabling
> vmalloc huge pages should still disable this alternate mode.

Yeah, this makes sense. I will fix it. 

> 
>> 		unsigned long size_per_node;
>> 
>> 		/*

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