linux-kernel - Re: [PATCH 10/14] arm64: kexec_file: load initrd, device-tree and purgatory segments

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Message-ID: <20170825013417.GA7282@akashi-kouhiroshi-no-MacBook-Air.local>
Date:   Fri, 25 Aug 2017 10:34:19 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     catalin.marinas@....com, will.deacon@....com,
        bauerman@...ux.vnet.ibm.com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, akpm@...ux-foundation.org, mpe@...erman.id.au,
        dyoung@...hat.com, bhe@...hat.com, arnd@...db.de,
        ard.biesheuvel@...aro.org, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 10/14] arm64: kexec_file: load initrd, device-tree and
 purgatory segments

On Thu, Aug 24, 2017 at 06:11:31PM +0100, Mark Rutland wrote:
> On Thu, Aug 24, 2017 at 05:18:07PM +0900, AKASHI Takahiro wrote:
> > load_other_segments() sets up and adds all the memory segments necessary
> > other than kernel, including initrd, device-tree blob and purgatory.
> > Most of the code was borrowed from kexec-tools' counterpart.
> > 
> > In addition, arch_kexec_image_probe(), arch_kexec_image_load() and
> > arch_kexec_kernel_verify_sig() are stubs for supporting multiple types
> > of kernel image formats.
> > 
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will.deacon@....com>
> > ---
> >  arch/arm64/include/asm/kexec.h         |  18 +++
> >  arch/arm64/kernel/machine_kexec_file.c | 255 +++++++++++++++++++++++++++++++++
> >  2 files changed, 273 insertions(+)
> 
> > +int load_other_segments(struct kimage *image, unsigned long kernel_load_addr,
> > +			char *initrd, unsigned long initrd_len,
> > +			char *cmdline, unsigned long cmdline_len)
> > +{
> > +	struct kexec_buf kbuf;
> > +	unsigned long initrd_load_addr = 0;
> > +	unsigned long purgatory_load_addr, dtb_load_addr;
> > +	char *dtb = NULL;
> > +	unsigned long dtb_len;
> > +	int ret = 0;
> > +
> > +	kbuf.image = image;
> > +
> > +	/* Load initrd */
> > +	if (initrd) {
> > +		kbuf.buffer = initrd;
> > +		kbuf.bufsz = initrd_len;
> > +		kbuf.memsz = initrd_len;
> > +		kbuf.buf_align = PAGE_SIZE;
> > +		/* within 1GB-aligned window of up to 32GB in size */
> > +		kbuf.buf_min = kernel_load_addr;
> > +		kbuf.buf_max = round_down(kernel_load_addr, SZ_1G)
> > +						+ (unsigned long)SZ_1G * 31;
> > +		kbuf.top_down = 0;
> > +
> > +		ret = kexec_add_buffer(&kbuf);
> > +		if (ret)
> > +			goto out_err;
> > +		initrd_load_addr = kbuf.mem;
> > +
> > +		pr_debug("Loaded initrd at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> > +				initrd_load_addr, initrd_len, initrd_len);
> > +	}
> > +
> > +	/* Load dtb blob */
> > +	ret = setup_dtb(image, initrd_load_addr, initrd_len,
> > +				cmdline, cmdline_len, &dtb, &dtb_len);
> > +	if (ret) {
> > +		pr_err("Preparing for new dtb failed\n");
> > +		goto out_err;
> > +	}
> > +
> > +	kbuf.buffer = dtb;
> > +	kbuf.bufsz = dtb_len;
> > +	kbuf.memsz = dtb_len;
> > +	/* not across 2MB boundary */
> > +	kbuf.buf_align = SZ_2M;
> > +	/*
> > +	 * Note for backporting:
> > +	 * On kernel prior to v4.2, fdt must reside within 512MB block
> > +	 * where the kernel also resides. So
> > +	 *   kbuf.buf_min = round_down(kernel_load_addr, SZ_512M);
> > +	 *   kbuf.buf_max = round_up(kernel_load_addr, SZ_512M);
> > +	 * would be required.
> > +	 */
> > +	kbuf.buf_min = kernel_load_addr;
> > +	kbuf.buf_max = ULONG_MAX;
> > +	kbuf.top_down = 1;
> 
> IIUC, this is trying to load the DTB above the kernel. Is that correct?

Yes.

> Assuming so, shouldn't that kernel_load_addr be kernel_load_addr +
> image_size from the kernel header?

Okey, it would be much safer.

> Otherwise, if the kernel is loaded close to the end of memory, the DTB
> could overlap.

Right, but we allocate the kernel from "bottom up"(top_down=0)
and such a corruption is very unlikely. If it happens, it means
that system memory is just too small.

Thanks,
-Takahiro AKASHI

> Thanks,
> Mark.