linux-kernel - Re: [PATCH v3 03/13] powerpc/mm: implement arch_flush_lazy_mmu

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Message-ID: <604f26cb-46c6-4533-8110-0b174eed821d@arm.com>
Date: Fri, 24 Oct 2025 14:09:21 +0200
From: Kevin Brodsky <kevin.brodsky@....com>
To: David Hildenbrand <david@...hat.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 03/13] powerpc/mm: implement arch_flush_lazy_mmu_mode()

On 23/10/2025 21:36, David Hildenbrand wrote:
> On 15.10.25 10:27, Kevin Brodsky wrote:
>> [...]
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> index 146287d9580f..7704dbe8e88d 100644
>> --- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> @@ -41,6 +41,16 @@ static inline void arch_enter_lazy_mmu_mode(void)
>>       batch->active = 1;
>>   }
>>   +static inline void arch_flush_lazy_mmu_mode(void)
>> +{
>> +    struct ppc64_tlb_batch *batch;
>> +
>> +    batch = this_cpu_ptr(&ppc64_tlb_batch);
>
> The downside is the double this_cpu_ptr() now on the
> arch_leave_lazy_mmu_mode() path.

This is only temporary, patch 9 removes it from arch_enter(). I don't
think having a redundant this_cpu_ptr() for a few commits is really a
concern?

Same idea for patch 4/10.

- Kevin