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[104.129.187.94]) by smtp.gmail.com with ESMTPSA id d76sm7941194pfd.185.2019.09.21.06.19.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 21 Sep 2019 06:19:52 -0700 (PDT) Subject: Re: [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared To: Matthew Wilcox , Jia He References: <20190920135437.25622-1-justin.he@arm.com> <20190920135437.25622-4-justin.he@arm.com> <20190920155300.GC15392@bombadil.infradead.org> From: Jia He Message-ID: Date: Sat, 21 Sep 2019 21:19:34 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20190920155300.GC15392@bombadil.infradead.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190921_061954_836386_E44F2B0D X-CRM114-Status: GOOD ( 19.77 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kaly Xin , Ralph Campbell , Andrew Morton , Suzuki Poulose , Catalin Marinas , Anshuman Khandual , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , James Morse , linux-arm-kernel@lists.infradead.org, Punit Agrawal , Marc Zyngier , Thomas Gleixner , nd@arm.com, Will Deacon , Alex Van Brunt , "Kirill A. Shutemov" , Robin Murphy Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org [On behalf of justin.he@arm.com] Hi Matthew On 2019/9/20 23:53, Matthew Wilcox wrote: > On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote: >> -static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma) >> +static inline int cow_user_page(struct page *dst, struct page *src, >> + struct vm_fault *vmf) >> { > Can we talk about the return type here? > >> + } else { >> + /* Other thread has already handled the fault >> + * and we don't need to do anything. If it's >> + * not the case, the fault will be triggered >> + * again on the same address. >> + */ >> + pte_unmap_unlock(vmf->pte, vmf->ptl); >> + return -1; > ... >> + return 0; >> } > So -1 for "try again" and 0 for "succeeded". > >> + if (cow_user_page(new_page, old_page, vmf)) { > Then we use it like a bool. But it's kind of backwards from a bool because > false is success. > >> + /* COW failed, if the fault was solved by other, >> + * it's fine. If not, userspace would re-fault on >> + * the same address and we will handle the fault >> + * from the second attempt. >> + */ >> + put_page(new_page); >> + if (old_page) >> + put_page(old_page); >> + return 0; > And we don't use the return value; in fact we invert it. > > Would this make more sense: > > static inline bool cow_user_page(struct page *dst, struct page *src, > struct vm_fault *vmf) > ... > pte_unmap_unlock(vmf->pte, vmf->ptl); > return false; > ... > return true; > ... > if (!cow_user_page(new_page, old_page, vmf)) { > > That reads more sensibly for me. We could also go with returning a > vm_fault_t, but that would be more complex than needed today, I think. Ok, will change the return type to bool as you suggested. Thanks --- Cheers, Justin (Jia He) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel