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Howlett" , Mark Brown , Andrew Morton , Jann Horn , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Peter Xu , linux-arm-kernel@lists.infradead.org, Will Deacon , Aishwarya TCV Subject: Re: [PATCH hotfix 6.12 v2 4/8] mm: resolve faulty mmap_region() error path behaviour Message-ID: References: <438f50c5-8b8c-444f-ae85-10e5151f3f24@lucifer.local> <57mgmdx7wgfwci3yo3ggkmcnm3ujamgkwcccm77ypvmer5tegn@opiq3ceh2uvy> <0b64edb9-491e-4dcd-8dc1-d3c8a336a49b@suse.cz> <1608957a-d138-4401-98ef-7fbe5fb7c387@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: C6701140006 X-Stat-Signature: d87ehfqct1ax3z4yzusphu6g5zk9cb34 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1730214268-436426 X-HE-Meta: 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 7XatD893 Hm7X2b7cOMKxq2wKtAoK5oh2fjiGD2uyWhQn7rHk6Ru5Es5D8VXGDUfDYaQqRLoN+etAGqVJLvjVmC2m9z8zPw8trHORdgO2r4ZMjNqtcpmeT5gA0F8FpTV+MwxycPuj0LzTjSjo3svdcZs6dEw+cdPcVHjBrE637bIUNMK+GyK6xOoT4NEQUAQd4JDCD88EPsZ/TXDdoGNxHMIkQsnPoyVAiuw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Lorenzo, Thanks for trying to fix this. On Mon, Oct 28, 2024 at 10:14:50PM +0000, Lorenzo Stoakes wrote: > From 247003cd2a4b5f4fc2dac97f5ef7e473a47f4324 Mon Sep 17 00:00:00 2001 > From: Lorenzo Stoakes > Date: Mon, 28 Oct 2024 22:05:44 +0000 > Subject: [PATCH] mm: perform MTE check within arm64 hook entirely > > It doesn't make sense to have shmem explicitly check this one arch-specific > case, it is arch-specific, so the arch should handle it. We know shmem is a > case in which we want to permit MTE, so simply check for this directly. > > This also fixes the issue with checking arch_validate_flags() early, which > would otherwise break mmap_region(). > > In order to implement this we must pass a file pointer, and additionally > update the sparc code to accept this parameter too. > > We'd ideally like to have eliminated the arch_calc_vm_flag_bits() case, but > we risk inadvertently changing behaviour as we do not have mmap() flags > available at the point of the arch_validate_flags() check and a MAP_ANON | > MAP_HUGETLB case would be accepted for MTE currently, but a MAP_SHARED | > MAP_HUGETLB would not. > > This is likely an oversight but we want to try to keep behaviour identical > to before in this patch. MAP_HUGETLB support for MTE is only in -next currently, so there wouldn't be any ABI change if we also allowed MAP_SHARED | MAP_HUGETLB. In 6.12, MAP_HUGETLB is not allowed to have PROT_MTE. > So continue to check VM_MTE_ALLOWED which arch_calc_vm_flag_bits() sets if > MAP_ANON. [...] > diff --git a/mm/shmem.c b/mm/shmem.c > index 4ba1d00fabda..e87f5d6799a7 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2733,9 +2733,6 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma) > if (ret) > return ret; > > - /* arm64 - allow memory tagging on RAM-based files */ > - vm_flags_set(vma, VM_MTE_ALLOWED); This breaks arm64 KVM if the VMM uses shared mappings for the memory slots (which is possible). We have kvm_vma_mte_allowed() that checks for the VM_MTE_ALLOWED flag as the VMM may not use PROT_MTE/VM_MTE directly. I need to read this thread properly but why not pass the file argument to arch_calc_vm_flag_bits() and set VM_MTE_ALLOWED in there? -- Catalin