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Biederman" Subject: Re: [PATCH v11 03/15] powerpc, kexec_file: factor out memblock-based arch_kexec_walk_mem() Message-ID: <20180720053333.GJ11258@linaro.org> Mail-Followup-To: AKASHI Takahiro , Dave Young , James Morse , catalin.marinas@arm.com, will.deacon@arm.com, dhowells@redhat.com, vgoyal@redhat.com, herbert@gondor.apana.org.au, davem@davemloft.net, bhe@redhat.com, arnd@arndb.de, ard.biesheuvel@linaro.org, bhsharma@redhat.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, "Eric W. Biederman" References: <20180711074203.3019-4-takahiro.akashi@linaro.org> <20180714015223.GA2745@dhcp-128-65.nay.redhat.com> <2a4ec965-5258-5835-3022-8f403a2f6bdd@arm.com> <20180716122412.GA7160@dhcp-128-65.nay.redhat.com> <20180717053104.GB11258@linaro.org> <20180717074923.GA8591@dhcp-128-65.nay.redhat.com> <20180718053818.GF11258@linaro.org> <20180718061350.GA5086@dhcp-128-65.nay.redhat.com> <20180718064041.GI11258@linaro.org> <20180718064519.GB5324@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180718064519.GB5324@dhcp-128-65.nay.redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dave, On Wed, Jul 18, 2018 at 02:45:19PM +0800, Dave Young wrote: > On 07/18/18 at 03:40pm, AKASHI Takahiro wrote: > > On Wed, Jul 18, 2018 at 02:13:50PM +0800, Dave Young wrote: > > > Hi AKASHI, > > > > > > On 07/18/18 at 02:38pm, AKASHI Takahiro wrote: > > > > Dave, > > > > > > > > On Tue, Jul 17, 2018 at 03:49:23PM +0800, Dave Young wrote: > > > > > Hi AKASHI, > > > > > On 07/17/18 at 02:31pm, AKASHI Takahiro wrote: > > > > > > Hi Dave, > > > > > > > > > > > > On Mon, Jul 16, 2018 at 08:24:12PM +0800, Dave Young wrote: > > > > > > > On 07/16/18 at 12:04pm, James Morse wrote: > > > > > > > > Hi Dave, > > > > > > > > > > > > > > > > On 14/07/18 02:52, Dave Young wrote: > > > > > > > > > On 07/11/18 at 04:41pm, AKASHI Takahiro wrote: > > > > > > > > >> Memblock list is another source for usable system memory layout. > > > > > > > > >> So powerpc's arch_kexec_walk_mem() is moved to kexec_file.c so that > > > > > > > > >> other memblock-based architectures, particularly arm64, can also utilise > > > > > > > > >> it. A moved function is now renamed to kexec_walk_memblock() and merged > > > > > > > > >> into the existing arch_kexec_walk_mem() for general use, either resource > > > > > > > > >> list or memblock list. > > > > > > > > >> > > > > > > > > >> A consequent function will not work for kdump with memblock list, but > > > > > > > > >> this will be fixed in the next patch. > > > > > > > > > > > > > > > > >> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > > > > > > > > > > > > > > > > >> @@ -513,6 +563,10 @@ static int locate_mem_hole_callback(struct resource *res, void *arg) > > > > > > > > >> int __weak arch_kexec_walk_mem(struct kexec_buf *kbuf, > > > > > > > > >> int (*func)(struct resource *, void *)) > > > > > > > > >> { > > > > > > > > >> + if (IS_ENABLED(CONFIG_HAVE_MEMBLOCK) && > > > > > > > > >> + !IS_ENABLED(CONFIG_ARCH_DISCARD_MEMBLOCK)) > > > > > > > > >> + return kexec_walk_memblock(kbuf, func); > > > > > > > > > > > > > > > > > > AKASHI, I'm not sure if this works on all arches, for example I chekced > > > > > > > > > the .config on my Nokia N900 kernel tree, there is HAVE_MEMBLOCK=y and > > > > > > > > > no CONFIG_ARCH_DISCARD_MEMBLOCK, in 32bit arm code no arch_kexec_walk_mem() > > > > > > > > By doesn't work you mean it's a change in behaviour? > > > > > > > > I think this is fine because 32bit arm doesn't support KEXEC_FILE, (this file is > > > > > > > > kexec_file specific right?). > > > > > > > > > > > > > > Ah, replied on a train, I forgot this is only for kexec_file, sorry > > > > > > > about that. Please ignore the comment. > > > > > > > > > > > > > > But since we have a weak function arch_kexec_walk_mem, adding another > > > > > > > condition branch within this weak function looks not good. > > > > > > > Something like below would be better: > > > > > > > > > > > > I see your concern here, but > > > > > > > > > > > > > > > > > > > int kexec_locate_mem_hole(struct kexec_buf *kbuf) > > > > > > > { > > > > > > > int ret; > > > > > > > > > > > > > > + if use memblock > > > > > > > + ret = kexec_walk_memblock() > > > > > > > + else > > > > > > > ret = arch_kexec_walk_mem(kbuf, locate_mem_hole_callback); > > > > > > > > > > > > > > return ret == 1 ? 0 : -EADDRNOTAVAIL; > > > > > > > } > > > > > > > > > > > > what if yet another architecture comes to kexec_file and wanna > > > > > > take a third approach? How can it override those functions? > > > > > > Depending on kernel configuration, it might re-define either > > > > > > kexec_walk_memblock() or arch_kexec_walk_mem(). It sounds weird to me. > > > > > > > > > > I also feel this weird, but it is slightly better because currently no > > > > > user need another overriding requirement, and I feel it is not expected to have in > > > > > the future for the memblock use. > > > > > > > > > > Rethinking about this issue, we can just remove the weak function and > > > > > just use general function. > > > > > > > > Do you really want to remove "weak" attribute? > > > > > > > > > Currently with your patch applied only s390 use arch_kexec_walk_mem like > > > > > below: > > > > > /* > > > > > * The kernel is loaded to a fixed location. Turn off kexec_locate_mem_hole > > > > > * and provide kbuf->mem by hand. > > > > > */ > > > > > int arch_kexec_walk_mem(struct kexec_buf *kbuf, > > > > > int (*func)(struct resource *, void *)) > > > > > { > > > > > return 1; > > > > > } > > > > > > > > > > AFAIK, all other users initialize kbuf->mem as NULL, so we can check > > > > > > > > As a matter of fact, nobody initializes kbuf->mem before calling > > > > kexec_add_buffer (in turn, kexec_locate_mem_hole()). > > > > > > Not sure we understand each other.. > > > Let's take an example in arch/x86/kernel/kexec-bzimage64.c: > > > bzImage64_load() : > > > struct kexec_buf kbuf = { .image = image, .buf_max = ULONG_MAX, > > > .top_down = true }; > > > > > > Except the three fields above other members will be initialized as zero > > > when compiling including the kbuf->mem > > > > Ah, you're right. > > (My armr64 patch doesn't use struct initializer, though.) > > > > > > > > > > > kbuf->mem in int kexec_locate_mem_hole: > > > > > > > > > > if (kbuf->mem) > > > > > return 0; > > > > > > > > > > if use memblock > > > > > kexec_walk_memblock > > > > > else > > > > > kexec_walk_mem > > > > > > kexec_walk_resource will be better than kexec_walk_mem > > > > > > > > > > > I think that your solution will work for existing architectures > > > > with appropriate patches, but to take your approach, as I said above, > > > > we will have to modify every call site on all kexec_file-capable architectures. > > > > > > > > If this is what you expect, I will work on it, but I don't think > > > > that it would be a better idea. > > > > So you would expect me to modify my own arm64 code as well as s390. > > Yes :) But I had not get time to read all your patches so I was not > aware the struct initialization in arm64 code so I assumed only s390 > need a change.. Okay, but I don't want to mix cross-arch changes into a single patch, prefer to leave the current patch as it is and add an additional patch as you suggested here. Is that OK for you? Thanks, -Takahiro AKASHI > Thanks > Dave