linux-kernel - Re: [PATCH v5 08/12] mm: enable lazy

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <0cb512ba-de15-4ba6-a85a-8287ab67fb53@arm.com>
Date: Thu, 27 Nov 2025 13:45:33 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Andreas Larsson <andreas@...sler.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>, Borislav Petkov
 <bp@...en8.de>, Catalin Marinas <catalin.marinas@....com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 David Hildenbrand <david@...hat.com>, "David S. Miller"
 <davem@...emloft.net>, David Woodhouse <dwmw2@...radead.org>,
 "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
 Jann Horn <jannh@...gle.com>, Juergen Gross <jgross@...e.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>,
 Mike Rapoport <rppt@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
 Peter Zijlstra <peterz@...radead.org>,
 "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
 Ryan Roberts <ryan.roberts@....com>, Suren Baghdasaryan <surenb@...gle.com>,
 Thomas Gleixner <tglx@...utronix.de>,
 Venkat Rao Bagalkote <venkat88@...ux.ibm.com>,
 Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
 Yeoreum Yun <yeoreum.yun@....com>, linux-arm-kernel@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
 xen-devel@...ts.xenproject.org, x86@...nel.org
Subject: Re: [PATCH v5 08/12] mm: enable lazy_mmu sections to nest

On 27/11/2025 13:33, Alexander Gordeev wrote:
> On Mon, Nov 24, 2025 at 01:22:24PM +0000, Kevin Brodsky wrote:
>
> Hi Kevin,
>
> ...
>> +/**
>> + * lazy_mmu_mode_pause() - Pause the lazy MMU mode.
>> + *
>> + * Pauses the lazy MMU mode; if it is currently active, disables it and calls
>> + * arch_leave_lazy_mmu_mode().
>> + *
>> + * Must be paired with a call to lazy_mmu_mode_resume(). Calls to the
>> + * lazy_mmu_mode_* API have no effect until the matching resume() call.
> Sorry if it was discussed already - if yes, I somehow missed it. If I read
> the whole thing correctly enter()/pause() interleaving is not forbidden?

Correct, any call inside pause()/resume() is now allowed (but
effectively ignored). See discussion with Ryan in v4 [1].

[1]
https://lore.kernel.org/all/824bf705-e9d6-4eeb-9532-9059fa56427f@arm.com/

> lazy_mmu_mode_enable()
> 	lazy_mmu_mode_pause()
> 		lazy_mmu_mode_enable()
> 		...
> 		lazy_mmu_mode_disable()
> 	lazy_mmu_mode_resume()
> lazy_mmu_mode_disable()
>
>> + *
>> + * Has no effect if called:
>> + * - While paused (inside another pause()/resume() pair)
>> + * - In interrupt context
>> + */
>>  static inline void lazy_mmu_mode_pause(void)
>>  {
>> +	struct lazy_mmu_state *state = &current->lazy_mmu_state;
>> +
>>  	if (in_interrupt())
>>  		return;
>>  
>> -	arch_leave_lazy_mmu_mode();
>> +	VM_WARN_ON_ONCE(state->pause_count == U8_MAX);
>> +
>> +	if (state->pause_count++ == 0 && state->enable_count > 0)
>> +		arch_leave_lazy_mmu_mode();
>>  }
>>  
>> +/**
>> + * lazy_mmu_mode_pause() - Resume the lazy MMU mode.
>                     resume() ?

Good catch! One copy-paste too many...

- Kevin

>> + *
>> + * Resumes the lazy MMU mode; if it was active at the point where the matching
>> + * call to lazy_mmu_mode_pause() was made, re-enables it and calls
>> + * arch_enter_lazy_mmu_mode().
>> + *
>> + * Must match a call to lazy_mmu_mode_pause().
>> + *
>> + * Has no effect if called:
>> + * - While paused (inside another pause()/resume() pair)
>> + * - In interrupt context
>> + */
>>  static inline void lazy_mmu_mode_resume(void)
>>  {
>> +	struct lazy_mmu_state *state = &current->lazy_mmu_state;
>> +
>>  	if (in_interrupt())
>>  		return;
>>  
>> -	arch_enter_lazy_mmu_mode();
>> +	VM_WARN_ON_ONCE(state->pause_count == 0);
>> +
>> +	if (--state->pause_count == 0 && state->enable_count > 0)
>> +		arch_enter_lazy_mmu_mode();
>>  }
> ...
> Thanks!