Date: Mon, 29 Oct 2018 20:21:18 +0200 From: Igor Stoppa <igor.stoppa@...il.com> To: Matthew Wilcox <willy@...radead.org> Cc: Mimi Zohar <zohar@...ux.vnet.ibm.com>, Kees Cook <keescook@...omium.org>, Dave Chinner <david@...morbit.com>, James Morris <jmorris@...ei.org>, Michal Hocko <mhocko@...nel.org>, kernel-hardening@...ts.openwall.com, linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, igor.stoppa@...wei.com, Dave Hansen <dave.hansen@...ux.intel.com>, Jonathan Corbet <corbet@....net>, Laura Abbott <labbott@...hat.com>, Vlastimil Babka <vbabka@...e.cz>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andrew Morton <akpm@...ux-foundation.org>, Pavel Tatashin <pasha.tatashin@...cle.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 08/17] prmem: struct page: track vmap_area On 25/10/2018 03:13, Matthew Wilcox wrote: > On Thu, Oct 25, 2018 at 02:01:02AM +0300, Igor Stoppa wrote: >>>> @@ -1747,6 +1750,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, >>>> if (!addr) >>>> return NULL; >>>> + va = __find_vmap_area((unsigned long)addr); >>>> + for (i = 0; i < va->vm->nr_pages; i++) >>>> + va->vm->pages[i]->area = va; >>> >>> I don't like it that you're calling this for _every_ vmalloc() caller >>> when most of them will never use this. Perhaps have page->va be initially >>> NULL and then cache the lookup in it when it's accessed for the first time. >>> >> >> If __find_vmap_area() was part of the API, this loop could be left out from >> __vmalloc_node_range() and the user of the allocation could initialize the >> field, if needed. >> >> What is the reason for keeping __find_vmap_area() private? > > Well, for one, you're walking the rbtree without holding the spinlock, > so you're going to get crashes. I don't see why we shouldn't export > find_vmap_area() though. Argh, yes, sorry. But find_vmap_area() would be enough for what I need. > Another way we could approach this is to embed the vmap_area in the > vm_struct. It'd require a bit of juggling of the alloc/free paths in > vmalloc, but it might be worthwhile. I have a feeling of unease about the whole vmap_area / vm_struct duality. They clearly are different types, with different purposes, but here and there there are functions that are named after some "area", yet they actually refer to vm_struct pointers. I wouldn't mind spending some time understanding the reason for this apparently bizarre choice, but after I have emerged from the prmem swamp. For now I'd stick to find_vmap_area(). -- igor
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