From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5046C43381 for ; Wed, 10 Mar 2021 22:12:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9520A64FCC for ; Wed, 10 Mar 2021 22:12:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233100AbhCJWLq (ORCPT ); Wed, 10 Mar 2021 17:11:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:52496 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232257AbhCJWLS (ORCPT ); Wed, 10 Mar 2021 17:11:18 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id B964364FAB; Wed, 10 Mar 2021 22:11:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615414278; bh=cJuiPe4bHTlhbjM/I/nNzyVykFnIqt93YhamnPmPPJ0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NdK4xPzvgCr+iQGiJ4yqvhPZZaSYpTdwN6zQ9BY4RaOpzgBC6IDblG4zn7Qd4rVNQ S8fy8lYB1k8X8fsCThEEyLhZKfly8JV+mmgbRk8hTUu7xsFCalWRGxPUHgTePmxGxN t65lOaHcZsHANzm5eOOuSttWHMptaFG54E98bz6OlrNOv0SD1vC+RL4fqOY/YUqBTi 8aACHJMDEcSAtSB5wrJwtrggR8CeQFb7P6OfLpT7frN26nk39EhJW0egx8l8J59UKX nCJDSzOSE1+fk4sC9JYVNlwJRwrmdy2uIgdkYiIaVpcgHlpCxf0Kk5qza/+mjH07V1 GLdMtzk/VlKKg== Date: Thu, 11 Mar 2021 00:10:54 +0200 From: Jarkko Sakkinen To: Kai Huang Cc: Dave Hansen , linux-sgx@vger.kernel.org, Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/5] x86/sgx: Use sgx_free_epc_page() in sgx_reclaim_pages() Message-ID: References: <20210303150323.433207-1-jarkko@kernel.org> <20210303150323.433207-3-jarkko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 11, 2021 at 09:36:15AM +1300, Kai Huang wrote: > On Wed, 2021-03-10 at 17:11 +0200, Jarkko Sakkinen wrote: > > On Wed, Mar 03, 2021 at 08:59:17AM -0800, Dave Hansen wrote: > > > On 3/3/21 7:03 AM, Jarkko Sakkinen wrote: > > > > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c > > > > index 52d070fb4c9a..ed99c60024dc 100644 > > > > --- a/arch/x86/kernel/cpu/sgx/main.c > > > > +++ b/arch/x86/kernel/cpu/sgx/main.c > > > > @@ -305,7 +305,6 @@ static void sgx_reclaim_pages(void) > > > >  { > > > >   struct sgx_epc_page *chunk[SGX_NR_TO_SCAN]; > > > >   struct sgx_backing backing[SGX_NR_TO_SCAN]; > > > > - struct sgx_epc_section *section; > > > >   struct sgx_encl_page *encl_page; > > > >   struct sgx_epc_page *epc_page; > > > >   pgoff_t page_index; > > > > @@ -378,11 +377,7 @@ static void sgx_reclaim_pages(void) > > > >   kref_put(&encl_page->encl->refcount, sgx_encl_release); > > > >   epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED; > > > >   > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - section = &sgx_epc_sections[epc_page->section]; > > > > - spin_lock(§ion->lock); > > > > - list_add_tail(&epc_page->list, §ion->page_list); > > > > - section->free_cnt++; > > > > - spin_unlock(§ion->lock); > > > > + sgx_free_epc_page(epc_page); > > > >   } > > > >  } > > > > > > In current upstream (3fb6d0e00e), sgx_free_epc_page() calls __eremove(). > > >  This code does not call __eremove(). That seems to be changing > > > behavior where none was intended. > > > > EREMOVE does not matter here, as it doesn't in almost all most of the sites > > where sgx_free_epc_page() is used in the driver. It does nothing to an > > uninitialized pages. > > Right. EREMOVE on uninitialized pages does nothing, so a more reasonable way is to > just NOT call EREMOVE (your original code), since it is absolutely unnecessary. > > I don't see ANY reason we should call EREMOVE here. > > Actually w/o my patch to split EREMOVE out of sgx_free_epc_page(), it then makes > perfect sense to have new sgx_free_epc_page() here. > > > > > The two patches that I posted originally for Kai's series took EREMOVE out > > of sgx_free_epc_page() and put an explicit EREMOVE where it is actually > > needed, but for reasons unknown to me, that change is gone. > > > > It's not gone. It goes into a new sgx_encl_free_epc_page(), which is exactly the same > as current sgx_free_epc_page() which as EREMOVE, instead of putting EREMOVE into a > dedicated sgx_reset_epc_page(), as you did in your series: > > https://lore.kernel.org/linux-sgx/20210113233541.17669-1-jarkko@kernel.org/ > > However, your change has side effort: it always put page back into free pool, even > EREMOVE fails. To make your change w/o having any functional change, it has to be: > > if(!sgx_reset_epc_page()) > sgx_free_epc_page(); OK, great, your patch set uses the wrapper only in the necessary call sites. Sorry, I overlooked this part. Anyway, it knowingly does that. I considered either as equally harmful side-ffects when I implemented. Either can only trigger, when there is a bug in the kernel code. It *could* do what that snippet suggest but it's like "out of the frying pan, into the fire" kind of change. Since NUMA patch set anyway requires to have a global dirty list, I think the better way to deal with this, would be to declare a new global in the patch under discussion: static struct list_head sgx_dirty_list; And sgx_encl_free_epc_page() could simply put the pages in this list. In some cases you could possibly even reset the system state using kexec for debugging purposes, so it could potentially bring a tiny bit of value. I can rebase then my NUMA patches on top of SGX specific KVM patches, once Boris have applied them. > And for this, Dave raised one concern we should add a WARN() to let user know EPC > page is leaked, and reboot is requied to get them back. > > However with sgx_reset_epc_page(), there's no place to add such WARN(), and > implementing original sgx_free_epc_page() as sgx_encl_free_epc_page() looks very > reasonable to me: > > https://www.spinics.net/lists/linux-sgx/msg04631.html /Jarkko