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(p200300d82f300b00cea90deed607041d.dip0.t-ipconnect.de. [2003:d8:2f30:b00:cea9:dee:d607:41d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42ac67845ccsm5465086f8f.36.2025.11.07.06.34.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 07 Nov 2025 06:34:05 -0800 (PST) Message-ID: Date: Fri, 7 Nov 2025 15:34:03 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 06/12] mm: introduce generic lazy_mmu helpers To: Ryan Roberts , Kevin Brodsky , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , "David S. Miller" , David Woodhouse , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org References: <20251029100909.3381140-1-kevin.brodsky@arm.com> <20251029100909.3381140-7-kevin.brodsky@arm.com> <71418b31-aedb-4600-9558-842515dd6c44@arm.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <71418b31-aedb-4600-9558-842515dd6c44@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >> #ifndef pte_batch_hint >> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c >> index 5d2a876035d6..c49b029d3593 100644 >> --- a/mm/kasan/shadow.c >> +++ b/mm/kasan/shadow.c >> @@ -305,7 +305,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr, >> pte_t pte; >> int index; >> >> - arch_leave_lazy_mmu_mode(); >> + lazy_mmu_mode_pause(); > > I wonder if there really are use cases that *require* pause/resume? I think > these kasan cases could be correctly implemented using a new nest level instead? > Are there cases where the effects really need to be immediate or do the effects > just need to be visible when you get to where the resume is? > > If the latter, that could just be turned into a nested disable (e.g. a flush). > In this case, there is only 1 PTE write so no benefit, but I wonder if other > cases may have more PTE writes that could then still be batched. It would be > nice to simplify the API by removing pause/resume if we can? It has clear semantics, clearer than some nest-disable IMHO. Maybe you can elaborate how you would change ("simplify") the API in that regard? What would the API look like?