From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751028AbeBIMlF (ORCPT ); Fri, 9 Feb 2018 07:41:05 -0500 Received: from mail-pl0-f68.google.com ([209.85.160.68]:33595 "EHLO mail-pl0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750863AbeBIMlD (ORCPT ); Fri, 9 Feb 2018 07:41:03 -0500 X-Google-Smtp-Source: AH8x227B6mGbYfPM4LwizvjDwSlRBK+JgvmnORBe/AkR3JeVlsTH0E5j59F5crk7iAeAl6iGx9bhEQ== Date: Fri, 9 Feb 2018 21:40:56 +0900 From: AKASHI Takahiro To: James Morse Cc: catalin.marinas@arm.com, will.deacon@arm.com, bauerman@linux.vnet.ibm.com, dhowells@redhat.com, vgoyal@redhat.com, herbert@gondor.apana.org.au, davem@davemloft.net, akpm@linux-foundation.org, mpe@ellerman.id.au, dyoung@redhat.com, bhe@redhat.com, arnd@arndb.de, ard.biesheuvel@linaro.org, julien.thierry@arm.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 05/11] arm64: kexec_file: create purgatory Message-ID: <20180209124055.xlwqdvb33uxsqlzh@fireball> Mail-Followup-To: AKASHI Takahiro , James Morse , catalin.marinas@arm.com, will.deacon@arm.com, bauerman@linux.vnet.ibm.com, dhowells@redhat.com, vgoyal@redhat.com, herbert@gondor.apana.org.au, davem@davemloft.net, akpm@linux-foundation.org, mpe@ellerman.id.au, dyoung@redhat.com, bhe@redhat.com, arnd@arndb.de, ard.biesheuvel@linaro.org, julien.thierry@arm.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20171204025801.12161-1-takahiro.akashi@linaro.org> <20171204025801.12161-6-takahiro.akashi@linaro.org> <5A7B475C.2080008@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5A7B475C.2080008@arm.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 07, 2018 at 06:37:16PM +0000, James Morse wrote: > Hi Akashi, > > On 04/12/17 02:57, AKASHI Takahiro wrote: > > This is a basic purgatory, or a kind of glue code between the two kernels, > > for arm64. > > > > Since purgatory is assumed to be relocatable (not executable) object by > > kexec generic code, arch_kexec_apply_relocations_add() is required in > > general. Arm64's purgatory, however, is a simple asm and all the references > > can be resolved as local, no re-linking is needed here. > > > > Please note that even if we don't support digest check at purgatory we > > (You knew what I was going to ask!) Yes, definitely. > > > need purgatory_sha_regions and purgatory_sha256_digest as they are > > referenced by generic kexec code. > > As somewhere to store the values? If we aren't doing the validation could we add > something about why not to the commit message? I think its because we only worry > about memory corruption for kdump, and for kdump we unmap the crash-kernel > region during normal-operation to prevent it getting corrupted. > > As we aren't doing the hash validation, could we hide its core-code behind some > ARCH_HAS_KEXEC_PURGATORY_HASH, instead of defining dummy symbols and doing > unnecessary work to fill them in? Yes, this is one idea. But as you mentioned below, adding a purgatory for arm64's kexec_file does make little sense as I've already removed digest check code after MarkR's comment. > > > diff --git a/arch/arm64/purgatory/entry.S b/arch/arm64/purgatory/entry.S > > new file mode 100644 > > index 000000000000..fe6e968076db > > --- /dev/null > > +++ b/arch/arm64/purgatory/entry.S > > @@ -0,0 +1,55 @@ > > +/* > > + * kexec core purgatory > > + */ > > +#include > > +#include > > + > > +#define SHA256_DIGEST_SIZE 32 /* defined in crypto/sha.h */ > > + > > +.text > > + > > +ENTRY(purgatory_start) > > + /* Start new image. */ > > + ldr x17, __kernel_entry > > + ldr x0, __dtb_addr > > + mov x1, xzr > > + mov x2, xzr > > + mov x3, xzr > > + br x17 > > +END(purgatory_start) > > Is this what arm64_relocate_new_kernel() drops into? I thought that had the > kernel boot register values already so we wouldn't need another trampoline for > kexec_file_load()... Indeed > .. but now that I look, it doesn't have the DTB, presumably because for regular > kexec we don't know where user-space put it. > > Could we add some x0_for_kexec that is 0 by default (if that's the ABI), or the First, I didn't get what you meaned here. After managing to modify my code, I found that we could re-use cpu_soft_restart(), especially, the fifth argument, which is currently contant 0, but we will be able to pass dtb address here. In turn, we can also use this argument to determine, in relocate_new_kernel(), whether we should call puragatory (kexec_load) or directly jump into the kernel (kexec_file_load). > DTB address for kexec_file_load()? This would avoid this extra trampoline, and > patching in the values from load_other_segments(). > > I'd love to avoid an in-kernel purgatory! (its code with funny > compile/link/relocation requirements that is impossible to debug) Lovely! I really appreicated your valuable comments. and more on other patches comming? -Takahiro AKASHI > > Thanks, > > James