From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from list by lists.gnu.org with archive (Exim 4.71) id 1aXpdT-0002yK-AZ for mharc-grub-devel@gnu.org; Mon, 22 Feb 2016 07:30:43 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43236) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aXpdO-0002vc-8H for grub-devel@gnu.org; Mon, 22 Feb 2016 07:30:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aXpdI-0001tO-Rp for grub-devel@gnu.org; Mon, 22 Feb 2016 07:30:38 -0500 Received: from mx2.suse.de ([195.135.220.15]:33838) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aXpdI-0001tG-Gc for grub-devel@gnu.org; Mon, 22 Feb 2016 07:30:32 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 583D8AC46; Mon, 22 Feb 2016 12:30:31 +0000 (UTC) Subject: Re: [PATCH v4 10/11] xen: modify page table construction To: Daniel Kiper References: <1456120999-5639-1-git-send-email-jgross@suse.com> <1456120999-5639-11-git-send-email-jgross@suse.com> <20160222091748.GO3482@olila.local.net-space.pl> <56CAD4E0.80304@suse.com> <20160222121858.GQ3482@olila.local.net-space.pl> From: Juergen Gross X-Enigmail-Draft-Status: N1110 Message-ID: <56CAFF66.1080709@suse.com> Date: Mon, 22 Feb 2016 13:30:30 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160222121858.GQ3482@olila.local.net-space.pl> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x (no timestamps) [generic] X-Received-From: 195.135.220.15 Cc: grub-devel@gnu.org, phcoder@gmail.com, mchang@suse.com, xen-devel@lists.xen.org X-BeenThere: grub-devel@gnu.org X-Mailman-Version: 2.1.14 Precedence: list Reply-To: The development of GNU GRUB List-Id: The development of GNU GRUB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Feb 2016 12:30:42 -0000 On 22/02/16 13:18, Daniel Kiper wrote: > On Mon, Feb 22, 2016 at 10:29:04AM +0100, Juergen Gross wrote: >> On 22/02/16 10:17, Daniel Kiper wrote: >>> On Mon, Feb 22, 2016 at 07:03:18AM +0100, Juergen Gross wrote: >>>> Modify the page table construction to allow multiple virtual regions >>>> to be mapped. This is done as preparation for removing the p2m list >>>> from the initial kernel mapping in order to support huge pv domains. >>>> >>>> This allows a cleaner approach for mapping the relocator page by >>>> using this capability. >>>> >>>> The interface to the assembler level of the relocator has to be changed >>>> in order to be able to process multiple page table areas. >>>> >>>> Signed-off-by: Juergen Gross >>>> --- >>>> V4: align variables in assembly sources >>>> use separate structure define as requested by Daniel Kiper >>>> >>>> V3: use constants instead of numbers as requested by Daniel Kiper >>>> add lots of comments to assembly code as requested by Daniel Kiper >>>> --- >>>> grub-core/lib/i386/xen/relocator.S | 88 ++++++---- >>>> grub-core/lib/x86_64/xen/relocator.S | 135 ++++++--------- >>>> grub-core/lib/xen/relocator.c | 28 ++- >>>> grub-core/loader/i386/xen.c | 325 ++++++++++++++++++++++++----------- >>>> include/grub/i386/memory.h | 7 + >>>> include/grub/xen/relocator.h | 6 +- >>>> 6 files changed, 359 insertions(+), 230 deletions(-) >>>> >>>> diff --git a/grub-core/lib/i386/xen/relocator.S b/grub-core/lib/i386/xen/relocator.S >>>> index 694a54c..f8d135a 100644 >>>> --- a/grub-core/lib/i386/xen/relocator.S >>>> +++ b/grub-core/lib/i386/xen/relocator.S >>>> @@ -102,6 +112,10 @@ VARIABLE(grub_relocator_xen_remap_continue) >>>> >>>> jmp *%eax >>>> >>>> + .p2align 2 >>> >>> I do not think this is needed but... >> >> Even if the processor does allow unaligned loads: it's cleaner to >> avoid them. > > I do not think that it pays here. However, if you are going > to leave .p2align please align other variables too. Which? The only candidate would be grub_relocator_xen_mmu_op which already is aligned due to above p2align. All other variables must be kept as they are, because they are part of instructions and alignment would break the code. > >>>> diff --git a/grub-core/lib/x86_64/xen/relocator.S b/grub-core/lib/x86_64/xen/relocator.S >>>> index 92e9e72..38ae157 100644 >>>> --- a/grub-core/lib/x86_64/xen/relocator.S >>>> +++ b/grub-core/lib/x86_64/xen/relocator.S >>>> >>>> jmp *%rax >>>> >>>> -LOCAL(mmu_op): >>>> + .p2align 3 >>> >>> Ditto... >>> >>>> diff --git a/grub-core/lib/xen/relocator.c b/grub-core/lib/xen/relocator.c >>>> index 8f427d3..a05b253 100644 >>>> --- a/grub-core/lib/xen/relocator.c >>>> +++ b/grub-core/lib/xen/relocator.c >>>> @@ -29,6 +29,11 @@ >>>> >>>> typedef grub_addr_t grub_xen_reg_t; >>>> >>>> +struct grub_relocator_xen_paging_area { >>>> + grub_xen_reg_t start; >>>> + grub_xen_reg_t size; >>>> +}; >>>> + >>> >>> ... this should have GRUB_PACKED because compiler may >>> add padding to align size member. >> >> Why would the compiler add padding to a structure containing two items >> of the same type? I don't think the C standard would allow this. >> >> grub_xen_reg_t is either unsigned (32 bit) or unsigned long (64 bit). >> There is no way this could require any padding. > > You are right but we should add this here just in case. Sorry, I don't think this makes any sense. The C standard is very clear in this case: a type requiring a special alignment has always a length being a multiple of that alignment. Otherwise arrays wouldn't work. Adding GRUB_PACKED would make the code less clear IMO. Finding such a qualifier in some code I want to modify would make me search for the reason for it which isn't existing. Juergen