From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f197.google.com (mail-lj1-f197.google.com [209.85.208.197]) by kanga.kvack.org (Postfix) with ESMTP id 373E76B000A for ; Thu, 4 Oct 2018 08:15:28 -0400 (EDT) Received: by mail-lj1-f197.google.com with SMTP id l11-v6so3548259ljb.2 for ; Thu, 04 Oct 2018 05:15:28 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id p20-v6sor592221ljg.43.2018.10.04.05.15.26 for (Google Transport Security); Thu, 04 Oct 2018 05:15:26 -0700 (PDT) MIME-Version: 1.0 References: <20181003185854.GA1174@jordon-HP-15-Notebook-PC> <20181003200003.GA9965@bombadil.infradead.org> <20181003221444.GZ30658@n2100.armlinux.org.uk> In-Reply-To: <20181003221444.GZ30658@n2100.armlinux.org.uk> From: Souptick Joarder Date: Thu, 4 Oct 2018 17:45:13 +0530 Message-ID: Subject: Re: [PATCH v2] mm: Introduce new function vm_insert_kmem_page Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Russell King - ARM Linux Cc: Matthew Wilcox , Miguel Ojeda , robin@protonic.nl, stefanr@s5r6.in-berlin.de, hjc@rock-chips.com, Heiko Stuebner , airlied@linux.ie, robin.murphy@arm.com, iamjoonsoo.kim@lge.com, Andrew Morton , Marek Szyprowski , Kees Cook , treding@nvidia.com, Michal Hocko , Dan Williams , "Kirill A. Shutemov" , Mark Rutland , aryabinin@virtuozzo.com, Dmitry Vyukov , Kate Stewart , tchibo@google.com, riel@redhat.com, Minchan Kim , Peter Zijlstra , "Huang, Ying" , ak@linux.intel.com, rppt@linux.vnet.ibm.com, linux@dominikbrodowski.net, Arnd Bergmann , cpandya@codeaurora.org, hannes@cmpxchg.org, Joe Perches , mcgrof@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux1394-devel@lists.sourceforge.net, dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org, Linux-MM On Thu, Oct 4, 2018 at 3:45 AM Russell King - ARM Linux wrote: > > On Wed, Oct 03, 2018 at 01:00:03PM -0700, Matthew Wilcox wrote: > > On Thu, Oct 04, 2018 at 12:28:54AM +0530, Souptick Joarder wrote: > > > These are the approaches which could have been taken to handle > > > this scenario - > > > > > > * Replace vm_insert_page with vmf_insert_page and then write few > > > extra lines of code to convert VM_FAULT_CODE to errno which > > > makes driver users more complex ( also the reverse mapping errno to > > > VM_FAULT_CODE have been cleaned up as part of vm_fault_t migration , > > > not preferred to introduce anything similar again) > > > > > > * Maintain both vm_insert_page and vmf_insert_page and use it in > > > respective places. But it won't gurantee that vm_insert_page will > > > never be used in #PF context. > > > > > > * Introduce a similar API like vm_insert_page, convert all non #PF > > > consumer to use it and finally remove vm_insert_page by converting > > > it to vmf_insert_page. > > > > > > And the 3rd approach was taken by introducing vm_insert_kmem_page(). > > > > > > In short, vmf_insert_page will be used in page fault handlers > > > context and vm_insert_kmem_page will be used to map kernel > > > memory to user vma outside page fault handlers context. > > > > As far as I can tell, vm_insert_kmem_page() is line-for-line identical > > with vm_insert_page(). Seriously, here's a diff I just did: > > > > -static int insert_page(struct vm_area_struct *vma, unsigned long addr, > > - struct page *page, pgprot_t prot) > > +static int insert_kmem_page(struct vm_area_struct *vma, unsigned long addr, > > + struct page *page, pgprot_t prot) > > - /* Ok, finally just insert the thing.. */ > > -int vm_insert_page(struct vm_area_struct *vma, unsigned long addr, > > +int vm_insert_kmem_page(struct vm_area_struct *vma, unsigned long addr, > > - return insert_page(vma, addr, page, vma->vm_page_prot); > > + return insert_kmem_page(vma, addr, page, vma->vm_page_prot); > > -EXPORT_SYMBOL(vm_insert_page); > > +EXPORT_SYMBOL(vm_insert_kmem_page); > > > > What on earth are you trying to do? > > Reading the commit log, it seems that the intention is to split out > vm_insert_page() used outside of page-fault handling with the use > within page-fault handling, so that different return codes can be > used. > > I don't see that justifies the code duplication - can't > vm_insert_page() and vm_insert_kmem_page() use the same mechanics > to do their job, and just translate the error code from the most- > specific to the least-specific error code? Do we really need two > copies of the same code just to return different error codes. Sorry about it. can I take below approach in a patch series -> create a wrapper function vm_insert_kmem_page using vm_insert_page. Convert all the non #PF users to use it. Then make vm_insert_page static and convert inline vmf_insert_page to caller.