linux-kernel - Re: [PATCH v4 01/12] powerpc/64s: Do not re-activate batched TLB flush

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Message-ID: <b3e4a92f-5b51-4eee-bfb8-c454add0f0d2@arm.com>
Date: Thu, 6 Nov 2025 10:29:50 +0000
From: Kevin Brodsky <kevin.brodsky@....com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.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 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>, 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,
 Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
Subject: Re: [PATCH v4 01/12] powerpc/64s: Do not re-activate batched TLB
 flush

On 05/11/2025 02:46, Ritesh Harjani (IBM) wrote:
> Kevin Brodsky <kevin.brodsky@....com> writes:
>
>> From: Alexander Gordeev <agordeev@...ux.ibm.com>
>>
>> Since commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash
>> lazy mmu mode") a task can not be preempted while in lazy MMU mode.
>> Therefore, the batch re-activation code is never called, so remove it.
>>
>> Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
>> ---
>>  arch/powerpc/include/asm/thread_info.h |  2 --
>>  arch/powerpc/kernel/process.c          | 25 -------------------------
>>  2 files changed, 27 deletions(-)
>>
> Since the commit referenced in above disables the preemption in
> arch_enter_lazy_mmu(), so the expectation is that we will never be
> context switched while in lazy_mmu, hence the code changes in
> switch_to() around __flush_tlb_pending() should ideally never be called.

Correct, that's the idea.

> With this analysis - the patch looks good to me. I will give this entire
> patch series a try on Power HW with Hash mmu too (which uses lazy mmu and
> let you know the results of that)!

That'd be very appreciated, thanks a lot!

> For this patch please feel free to add:
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
>
>
> CC: Venkat who also runs CI on linux Power HW for upstream testing :)

Ack, will Cc you both in the next version.

- Kevin