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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id y15sm11968095wrm.93.2021.02.08.10.18.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Feb 2021 10:18:57 -0800 (PST) To: Christoph Hellwig Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, jgg@ziepe.ca, linux-mm@kvack.org, Andrew Morton , dan.j.williams@intel.com References: <20210205103259.42866-1-pbonzini@redhat.com> <20210205103259.42866-2-pbonzini@redhat.com> <20210208173936.GA1496438@infradead.org> From: Paolo Bonzini Subject: Re: [PATCH 1/2] mm: provide a sane PTE walking API for modules Message-ID: <3b10057c-e117-89fa-1bd4-23fb5a4efb5f@redhat.com> Date: Mon, 8 Feb 2021 19:18:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210208173936.GA1496438@infradead.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/21 18:39, Christoph Hellwig wrote: >> +int follow_pte(struct mm_struct *mm, unsigned long address, >> + pte_t **ptepp, spinlock_t **ptlp) >> +{ >> + return follow_invalidate_pte(mm, address, NULL, ptepp, NULL, ptlp); >> +} >> +EXPORT_SYMBOL_GPL(follow_pte); > > I still don't think this is good as a general API. Please document this > as KVM only for now, and hopefully next merge window I'll finish an > export variant restricting us to specific modules. Fair enough. I would expect that pretty much everyone using follow_pfn will at least want to switch to this one (as it's less bad and not impossible to use correctly), but I'll squash this in: diff --git a/include/linux/mm.h b/include/linux/mm.h index 90b527260edf..24b292fce8e5 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1659,8 +1659,8 @@ void free_pgd_range(struct mmu_gather *tlb, unsigned long addr, int copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma); int follow_invalidate_pte(struct mm_struct *mm, unsigned long address, - struct mmu_notifier_range *range, pte_t **ptepp, pmd_t **pmdpp, - spinlock_t **ptlp); + struct mmu_notifier_range *range, pte_t **ptepp, + pmd_t **pmdpp, spinlock_t **ptlp); int follow_pte(struct mm_struct *mm, unsigned long address, pte_t **ptepp, spinlock_t **ptlp); int follow_pfn(struct vm_area_struct *vma, unsigned long address, diff --git a/mm/memory.c b/mm/memory.c index 3632f7416248..c8679b15c004 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4792,6 +4792,9 @@ int follow_invalidate_pte(struct mm_struct *mm, unsigned long address, * Only IO mappings and raw PFN mappings are allowed. The mmap semaphore * should be taken for read. * + * KVM uses this function. While it is arguably less bad than + * ``follow_pfn``, it is not a good general-purpose API. + * * Return: zero on success, -ve otherwise. */ int follow_pte(struct mm_struct *mm, unsigned long address, @@ -4809,6 +4812,9 @@ EXPORT_SYMBOL_GPL(follow_pte); * * Only IO mappings and raw PFN mappings are allowed. * + * This function does not allow the caller to read the permissions + * of the PTE. Do not use it. + * * Return: zero and the pfn at @pfn on success, -ve otherwise. */ int follow_pfn(struct vm_area_struct *vma, unsigned long address, (apologies in advance if Thunderbird destroys the patch). Paolo