linux-kernel - Re: [PATCH v3 11/13] x86/xen: use lazy_mmu

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

Message-ID: <1f81548e-18f2-49bf-82bc-e0dc667b78fd@redhat.com>
Date: Fri, 24 Oct 2025 17:16:56 +0200
From: David Hildenbrand <david@...hat.com>
To: David Woodhouse <dwmw2@...radead.org>,
 Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, Alexander Gordeev <agordeev@...ux.ibm.com>,
 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 S. Miller" <davem@...emloft.net>, "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>, Ryan Roberts <ryan.roberts@....com>,
 Suren Baghdasaryan <surenb@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>, 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 v3 11/13] x86/xen: use lazy_mmu_state when
 context-switching

On 24.10.25 17:13, David Woodhouse wrote:
> On Fri, 2025-10-24 at 16:51 +0200, David Hildenbrand wrote:
>> On 24.10.25 16:47, David Woodhouse wrote:
>>> On Thu, 2025-10-23 at 22:06 +0200, David Hildenbrand wrote:
>>>> On 15.10.25 10:27, Kevin Brodsky wrote:
>>>>> We currently set a TIF flag when scheduling out a task that is in
>>>>> lazy MMU mode, in order to restore it when the task is scheduled
>>>>> again.
>>>>>
>>>>> The generic lazy_mmu layer now tracks whether a task is in lazy MMU
>>>>> mode in task_struct::lazy_mmu_state. We can therefore check that
>>>>> state when switching to the new task, instead of using a separate
>>>>> TIF flag.
>>>>>
>>>>> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
>>>>> ---
>>>>
>>>>
>>>> Looks ok to me, but I hope we get some confirmation from x86 / xen
>>>> folks.
>>>
>>>
>>> I know tglx has shouted at me in the past for precisely this reminder,
>>> but you know you can test Xen guests under QEMU/KVM now and don't need
>>> to actually run Xen? Has this been boot tested?
>>
>> And after that, boot-testing sparc as well? :D
> 
> Also not that hard in QEMU, I believe. Although I do have some SPARC
> boxes in the shed...

Yeah, I once went through the pain of getting a sparc64 system booting 
in QEMU with a distro (was it debian?) that was 7 years old or so.

Fantastic experience.

Only took me 2 days IIRC. Absolutely worth it to not break upstream 
kernels on a museum piece.

-- 
Cheers

David / dhildenb