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Tue, 11 Nov 2025 22:09:07 -0800 (PST) Received: from dw-tp ([49.207.219.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2984dbd8cd0sm18094405ad.4.2025.11.11.22.09.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Nov 2025 22:09:06 -0800 (PST) From: Ritesh Harjani (IBM) To: Dave Vasilevsky , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Nadav Amit , "Peter Zijlstra (Intel)" , Andrew Morton Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Dave Vasilevsky Subject: Re: [PATCH v2] powerpc, mm: Fix mprotect on book3s 32-bit In-Reply-To: <20251111-vasi-mprotect-g3-v2-1-881c94afbc42@vasilevsky.ca> Date: Wed, 12 Nov 2025 11:03:52 +0530 Message-ID: <87ikff95mn.ritesh.list@gmail.com> References: <20251111-vasi-mprotect-g3-v2-1-881c94afbc42@vasilevsky.ca> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Dave Vasilevsky writes: > On 32-bit book3s with hash-MMUs, tlb_flush() was a no-op. This was > unnoticed because all uses until recently were for unmaps, and thus > handled by __tlb_remove_tlb_entry(). > > After commit 4a18419f71cd ("mm/mprotect: use mmu_gather") in kernel 5.19, > tlb_gather_mmu() started being used for mprotect as well. This caused > mprotect to simply not work on these machines: > > int *ptr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, > MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); > *ptr = 1; // force HPTE to be created > mprotect(ptr, 4096, PROT_READ); > *ptr = 2; // should segfault, but succeeds > > Fixed by making tlb_flush() actually flush TLB pages. This finally > agrees with the behaviour of boot3s64's tlb_flush(). > > Fixes: 4a18419f71cd ("mm/mprotect: use mmu_gather") > Signed-off-by: Dave Vasilevsky > Cc: stable@vger.kernel.org > --- > Changes in v2: > - Flush entire TLB if full mm is requested. > - Link to v1: https://lore.kernel.org/r/20251027-vasi-mprotect-g3-v1-1-3c5187085f9a@vasilevsky.ca > --- > arch/powerpc/include/asm/book3s/32/tlbflush.h | 8 ++++++-- > arch/powerpc/mm/book3s32/tlb.c | 9 +++++++++ > 2 files changed, 15 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/include/asm/book3s/32/tlbflush.h b/arch/powerpc/include/asm/book3s/32/tlbflush.h > index e43534da5207aa3b0cb3c07b78e29b833c141f3f..b8c587ad2ea954f179246a57d6e86e45e91dcfdc 100644 > --- a/arch/powerpc/include/asm/book3s/32/tlbflush.h > +++ b/arch/powerpc/include/asm/book3s/32/tlbflush.h > @@ -11,6 +11,7 @@ > void hash__flush_tlb_mm(struct mm_struct *mm); > void hash__flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr); > void hash__flush_range(struct mm_struct *mm, unsigned long start, unsigned long end); > +void hash__flush_gather(struct mmu_gather *tlb); Maybe I would have preferred the following naming convention for hash specific tlb_flush w.r.t mmu_gather, which is also similar to what book3s64 uses ;) - hash__tlb_flush() But no strong objection on this either. BTW - I did run your test program in Qemu and I was able to reproduce the problem, and this patch fixes it. The change overall looks good to me. So, please feel free to add: Reviewed-by: Ritesh Harjani (IBM)