From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752799AbeCFI2B (ORCPT ); Tue, 6 Mar 2018 03:28:01 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:40523 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750769AbeCFI17 (ORCPT ); Tue, 6 Mar 2018 03:27:59 -0500 X-Google-Smtp-Source: AG47ELvvb7Jngklu5fIYvwWILlS5th7ZXufmFC+IhuA7/uvUwWDFVGa7uXNEIZdalZbYu4vl8nMVoA== Date: Tue, 6 Mar 2018 11:27:43 +0300 From: "Kirill A. Shutemov" To: Dave Hansen Cc: "Kirill A. Shutemov" , Ingo Molnar , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Tom Lendacky , Kai Huang , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC, PATCH 13/22] mm, rmap: Free encrypted pages once mapcount drops to zero Message-ID: <20180306082743.2epdfxv4ds7hz7py@node.shutemov.name> References: <20180305162610.37510-1-kirill.shutemov@linux.intel.com> <20180305162610.37510-14-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180223 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 05, 2018 at 11:13:36AM -0800, Dave Hansen wrote: > On 03/05/2018 08:26 AM, Kirill A. Shutemov wrote: > > @@ -1292,6 +1308,12 @@ static void page_remove_anon_compound_rmap(struct page *page) > > __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr); > > deferred_split_huge_page(page); > > } > > + > > + anon_vma = page_anon_vma(page); > > + if (anon_vma_encrypted(anon_vma)) { > > + int keyid = anon_vma_keyid(anon_vma); > > + free_encrypt_page(page, keyid, compound_order(page)); > > + } > > } > > It's not covered in the description and I'm to lazy to dig into it, so: > Without this code, where do they get freed? Why does it not cause any > problems to free them here? It's the only place where we get it freed. "Freeing" is not the best terminology here, but I failed to come up with something batter. We prepare the encryption page to being freed: flush the cache in MKTME case. The page itself gets freed later in a usual manner: once refcount drops to zero. The problem is that we may not have valid anon_vma around once mapcount drops to zero, so we have to do "freeing" here. For anonymous memory once mapcount dropped to zero there's no way it will get mapped back to userspace. page_remove_anon Kernel still will be able to access the page with kmap() and I will need to be very careful to get it right wrt cache management. I'll update the description. -- Kirill A. Shutemov