| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <e6e3137c-3b0a-4c92-9e5f-69bee5e0c948@linux.alibaba.com>
Date: Thu, 12 Jun 2025 21:25:43 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
hughd@...gle.com
Cc: lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, npache@...hat.com,
ryan.roberts@....com, dev.jain@....com, ziy@...dia.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: huge_memory: disallow hugepages if the
system-wide THP sysfs settings are disabled
On 2025/6/12 21:05, David Hildenbrand wrote:
> On 12.06.25 14:45, Baolin Wang wrote:
>>
>>
>> On 2025/6/12 16:51, David Hildenbrand wrote:
>>> On 12.06.25 09:51, Baolin Wang wrote:
>>>>
>>>>
>>>> On 2025/6/11 20:34, David Hildenbrand wrote:
>>>>> On 05.06.25 10:00, Baolin Wang wrote:
>>>>>> The MADV_COLLAPSE will ignore the system-wide Anon THP sysfs
>>>>>> settings,
>>>>>> which
>>>>>> means that even though we have disabled the Anon THP configuration,
>>>>>> MADV_COLLAPSE
>>>>>> will still attempt to collapse into a Anon THP. This violates the
>>>>>> rule
>>>>>> we have
>>>>>> agreed upon: never means never.
>>>>>>
>>>>>> Another rule for madvise, referring to David's suggestion: “allowing
>>>>>> for collapsing
>>>>>> in a VM without VM_HUGEPAGE in the "madvise" mode would be fine".
>>>>>>
>>>>>> To address this issue, should check whether the Anon THP
>>>>>> configuration
>>>>>> is disabled
>>>>>> in thp_vma_allowable_orders(), even when the TVA_ENFORCE_SYSFS
>>>>>> flag is
>>>>>> set.
>>>>>>
>>>>>> In summary, the current strategy is:
>>>>>>
>>>>>> 1. If always & orders == 0, and madvise & orders == 0, and
>>>>>> hugepage_global_enabled() == false
>>>>>> (global THP settings are not enabled), it means mTHP of that orders
>>>>>> are prohibited
>>>>>> from being used, then madvise_collapse() is forbidden for that
>>>>>> orders.
>>>>>>
>>>>>> 2. If always & orders == 0, and madvise & orders == 0, and
>>>>>> hugepage_global_enabled() == true
>>>>>> (global THP settings are enabled), and inherit & orders == 0, it
>>>>>> means
>>>>>> mTHP of that
>>>>>> orders are still prohibited from being used, thus madvise_collapse()
>>>>>> is not allowed
>>>>>> for that orders.
>>>>>>
>>>>>> Reviewed-by: Zi Yan <ziy@...dia.com>
>>>>>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>>>>> ---
>>>>>> include/linux/huge_mm.h | 23 +++++++++++++++++++----
>>>>>> 1 file changed, 19 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>>>>> index 2f190c90192d..199ddc9f04a1 100644
>>>>>> --- a/include/linux/huge_mm.h
>>>>>> +++ b/include/linux/huge_mm.h
>>>>>> @@ -287,20 +287,35 @@ unsigned long thp_vma_allowable_orders(struct
>>>>>> vm_area_struct *vma,
>>>>>> unsigned long orders)
>>>>>> {
>>>>>> /* Optimization to check if required orders are enabled
>>>>>> early. */
>>>>>> - if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
>>>>>> - unsigned long mask = READ_ONCE(huge_anon_orders_always);
>>>>>> + if (vma_is_anonymous(vma)) {
>>>>>> + unsigned long always = READ_ONCE(huge_anon_orders_always);
>>>>>> + unsigned long madvise = READ_ONCE(huge_anon_orders_madvise);
>>>>>> + unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);
>>>>>> + unsigned long mask = always | madvise;
>>>>>> +
>>>>>> + /*
>>>>>> + * If the system-wide THP/mTHP sysfs settings are disabled,
>>>>>> + * then we should never allow hugepages.
>>>>> > + */> + if (!(mask & orders) &&
>>>>> !(hugepage_global_enabled() && (inherit & orders)))
>>>>>> + return 0;
>>>>>
>>>>> I'm still trying to digest that. Isn't there a way for us to work with
>>>>> the orders,
>>>>> essentially masking off all orders that are forbidden globally.
>>>>> Similar
>>>>> to below, if !orders, then return 0?
>>>>> /* Orders disabled directly. */
>>>>> orders &= ~TODO;
>>>>> /* Orders disabled by inheriting from the global toggle. */
>>>>> if (!hugepage_global_enabled())
>>>>> orders &= ~READ_ONCE(huge_anon_orders_inherit);
>>>>>
>>>>> TODO is probably a -1ULL and then clearing always/madvise/inherit.
>>>>> Could
>>>>> add a simple helper for that
>>>>>
>>>>> huge_anon_orders_never
>>>>
>>>> I followed Lorenzo's suggestion to simplify the logic. Does that look
>>>> more readable?
>>>>
>>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>>> index 2f190c90192d..3087ac7631e0 100644
>>>> --- a/include/linux/huge_mm.h
>>>> +++ b/include/linux/huge_mm.h
>>>> @@ -265,6 +265,43 @@ unsigned long __thp_vma_allowable_orders(struct
>>>> vm_area_struct *vma,
>>>> unsigned long tva_flags,
>>>> unsigned long orders);
>>>>
>>>> +/* Strictly mask requested anonymous orders according to sysfs
>>>> settings. */
>>>> +static inline unsigned long __thp_mask_anon_orders(unsigned long
>>>> vm_flags,
>>>> + unsigned long tva_flags, unsigned long
>>>> orders)
>>>> +{
>>>> + unsigned long always = READ_ONCE(huge_anon_orders_always);
>>>> + unsigned long madvise = READ_ONCE(huge_anon_orders_madvise);
>>>> + unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);
>>>> + bool inherit_enabled = hugepage_global_enabled();
>>>> + bool has_madvise = vm_flags & VM_HUGEPAGE;
>>>> + unsigned long mask = always | madvise;
>>>> +
>>>> + mask = always | madvise;
>>>> + if (inherit_enabled)
>>>> + mask |= inherit;
>>>> +
>>>> + /* All set to/inherit NEVER - never means never globally,
>>>> abort. */
>>>> + if (!(mask & orders))
>>>> + return 0;
>>>
>>> Still confusing. I am not sure if we would properly catch when someone
>>> specifies e.g., 2M and 1M, while we only have 2M disabled.
>>
>> IIUC, Yes. In your case, we will only allow order 8 (1M mTHP).
>>
>>> I would rewrite the function to only ever substract from "orders".
>>>
>>> ...
>>>
>>> /* Disallow orders that are set to NEVER directly ... */
>>> order &= (always | madvise | inherit);
>>>
>>> /* ... or through inheritance. */
>>> if (inherit_enabled)
>>> orders &= ~inherit;
>>
>> Sorry, I didn't get you here.
>>
>> If orders = THP_ORDERS_ALL_ANON, inherit = 0x200 (order 9), always and
>> madvise are 0, and inherit_enabled = true. Then orders will be 0 with
>> your logic. But we should allow order 9, right?
>
> Yeah, all confusing, because the temporary variables don't help.
>
> if (!inherit_enabled)
>
> or simply
>
> if (!hugepage_global_enabled();)
>
> Let me try again below.
>
>>
>>>
>>> /*
>>> * Otherwise, we only enforce sysfs settings if asked. In addition,
>>> * if the user sets a sysfs mode of madvise and if TVA_ENFORCE_SYSFS
>>> * is not set, we don't bother checking whether the VMA has
>>> VM_HUGEPAGE
>>> * set.
>>> */
>>> if (!orders || !(tva_flags & TVA_ENFORCE_SYSFS))
>>> return orders;
>>>
>>>> +
>>>> + /*
>>>> + * Otherwise, we only enforce sysfs settings if asked. In
>>>> addition,
>>>> + * if the user sets a sysfs mode of madvise and if
>>>> TVA_ENFORCE_SYSFS
>>>> + * is not set, we don't bother checking whether the VMA has
>>>> VM_HUGEPAGE
>>>> + * set.
>>>> + */
>>>> + if (!(tva_flags & TVA_ENFORCE_SYSFS))
>>>> + return orders;
>>>> +
>>>> + mask = always;
>>>> + if (has_madvise)
>>>> + mask |= madvise;
>>>> + if (hugepage_global_always() || (has_madvise &&
>>>> inherit_enabled))
>>>> + mask |= inherit;
>>>
>>> Similarly, this can maybe become (not 100% sure if I got it right, the
>>> condition above is confusing)
>>
>> IMO, this is the original logic.
>
> Yeah, and it's absolutely confusing stuff.
>
> Let me try again by only clearing flags. Maybe this would be clearer?
> (and correct? still confused why the latter part is so complicated in
> existing
> code)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 8b8f353cc7b81..66fdfe06e4996 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -265,6 +265,42 @@ unsigned long __thp_vma_allowable_orders(struct
> vm_area_struct *vma,
> unsigned long tva_flags,
> unsigned long orders);
>
> +/* Strictly mask requested anonymous orders according to sysfs
> settings. */
> +static inline unsigned long __thp_mask_anon_orders(unsigned long vm_flags,
> + unsigned long tva_flags, unsigned long orders)
> +{
> + const unsigned long always = READ_ONCE(huge_anon_orders_always);
> + const unsigned long madvise = READ_ONCE(huge_anon_orders_madvise);
> + const unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);
> + const unsigned long never = ~(always | madvise | inherit);
> +
> + /* Disallow orders that are set to NEVER directly ... */
> + orders &= ~never;
> +
> + /* ... or through inheritance (global == NEVER). */
> + if (!hugepage_global_enabled())
> + orders &= ~inherit;
> +
> + /*
> + * Otherwise, we only enforce sysfs settings if asked. In addition,
> + * if the user sets a sysfs mode of madvise and if
> TVA_ENFORCE_SYSFS
> + * is not set, we don't bother checking whether the VMA has
> VM_HUGEPAGE
> + * set.
> + */
> + if (!(tva_flags & TVA_ENFORCE_SYSFS))
> + return orders;
> +
> + if (!(vm_flags & VM_HUGEPAGE)) {
> + /* Disallow orders that are set to MADVISE directly ... */
> + orders &= ~madvise;
> +
> + /* ... or through inheritance (global == MADVISE). */
> + if (!hugepage_global_always())
> + orders &= ~inherit;
Seems we can drop this 'inherit' check, cause if
!hugepage_global_enabled() == true, which always means
!hugepage_global_always() is true.
> + }
> + return orders;
> +}
Otherwise look good to me.
> +
> /**
> * thp_vma_allowable_orders - determine hugepage orders that are
> allowed for vma
> * @vma: the vm area to check
> @@ -287,16 +323,8 @@ unsigned long thp_vma_allowable_orders(struct
> vm_area_struct *vma,
> unsigned long orders)
> {
> /* Optimization to check if required orders are enabled early. */
> - if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
> - unsigned long mask = READ_ONCE(huge_anon_orders_always);
> -
> - if (vm_flags & VM_HUGEPAGE)
> - mask |= READ_ONCE(huge_anon_orders_madvise);
> - if (hugepage_global_always() ||
> - ((vm_flags & VM_HUGEPAGE) &&
> hugepage_global_enabled()))
> - mask |= READ_ONCE(huge_anon_orders_inherit);
> -
> - orders &= mask;
> + if (vma_is_anonymous(vma)) {
> + orders = __thp_mask_anon_orders(vm_flags, tva_flags,
> orders);
> if (!orders)
> return 0;
> }
>
>
Powered by blists - more mailing lists