Re: [PATCH v9 04/11] arm64: kexec_file: allocate memory walking through memblock list

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

James,

On Tue, May 01, 2018 at 06:46:09PM +0100, James Morse wrote:
> Hi Akashi,
> 
> On 25/04/18 07:26, AKASHI Takahiro wrote:
> > We need to prevent firmware-reserved memory regions, particularly EFI
> > memory map as well as ACPI tables, from being corrupted by loading
> > kernel/initrd (or other kexec buffers). We also want to support memory
> > allocation in top-down manner in addition to default bottom-up.
> > So let's have arm64 specific arch_kexec_walk_mem() which will search
> > for available memory ranges in usable memblock list,
> > i.e. !NOMAP & !reserved, 
> 
> > instead of system resource tree.
> 
> Didn't we try to fix the system-resource-tree in order to fix regular-kexec to
> be safe in the EFI-memory-map/ACPI-tables case?
> 
> It would be good to avoid having two ways of doing this, and I would like to
> avoid having extra arch code...

I know what you mean.
/proc/iomem or system resource is, in my opinion, not the best place to
describe memory usage of kernel but rather to describe *physical* hardware
layout. As we are still discussing about "reserved" memory, I don't want
to depend on it.
Along with memblock list, we will have more accurate control over memory
usage.

> 
> > diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> > new file mode 100644
> > index 000000000000..f9ebf54ca247
> > --- /dev/null
> > +++ b/arch/arm64/kernel/machine_kexec_file.c
> > @@ -0,0 +1,57 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * kexec_file for arm64
> > + *
> > + * Copyright (C) 2018 Linaro Limited
> > + * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > + *
> 
> > + * Most code is derived from arm64 port of kexec-tools
> 
> How does kexec-tools walk memblock?

Will remove this comment from this patch.
Obviously, this comment is for the rest of the code which will be
added to succeeding patches (patch #5 and #7).


> 
> > + */
> > +
> > +#define pr_fmt(fmt) "kexec_file: " fmt
> > +
> > +#include <linux/ioport.h>
> > +#include <linux/kernel.h>
> > +#include <linux/kexec.h>
> > +#include <linux/memblock.h>
> > +
> > +int arch_kexec_walk_mem(struct kexec_buf *kbuf,
> > +				int (*func)(struct resource *, void *))
> > +{
> > +	phys_addr_t start, end;
> > +	struct resource res;
> > +	u64 i;
> > +	int ret = 0;
> > +
> > +	if (kbuf->image->type == KEXEC_TYPE_CRASH)
> > +		return func(&crashk_res, kbuf);
> > +
> > +	if (kbuf->top_down)
> > +		for_each_mem_range_rev(i, &memblock.memory, &memblock.reserved,
> > +				NUMA_NO_NODE, MEMBLOCK_NONE,
> > +				&start, &end, NULL) {
> 
> for_each_free_mem_range_reverse() is a more readable version of this helper.

OK. I used to use my own limited list of reserved memory instead of
memblock.reserved here to exclude verbose ranges.


> > +			if (!memblock_is_map_memory(start))
> > +				continue;
> 
> Passing MEMBLOCK_NONE means this walk will never find MEMBLOCK_NOMAP memory.

Sure, I confirmed it.

> 
> > +			res.start = start;
> > +			res.end = end;
> > +			ret = func(&res, kbuf);
> > +			if (ret)
> > +				break;
> > +		}
> > +	else
> > +		for_each_mem_range(i, &memblock.memory, &memblock.reserved,
> > +				NUMA_NO_NODE, MEMBLOCK_NONE,
> > +				&start, &end, NULL) {
> 
> for_each_free_mem_range()?

OK.

> > +			if (!memblock_is_map_memory(start))
> > +				continue;
> > +
> > +			res.start = start;
> > +			res.end = end;
> > +			ret = func(&res, kbuf);
> > +			if (ret)
> > +				break;
> > +		}
> > +
> > +	return ret;
> > +}
> > 
> 
> With these changes, what we have is almost:
> arch/powerpc/kernel/machine_kexec_file_64.c::arch_kexec_walk_mem() !
> (the difference being powerpc doesn't yet support crash-kernels here)
> 
> If the argument is walking memblock gives a better answer than the stringy
> walk_system_ram_res() thing, is there any mileage in moving this code into
> kexec_file.c, and using it if !IS_ENABLED(CONFIG_ARCH_DISCARD_MEMBLOCK)?
> 
> This would save arm64/powerpc having near-identical implementations.
> 32bit arm keeps memblock if it has kexec, so it may be useful there too if
> kexec_file_load() support is added.

Thanks. I've forgot ppc.

-Takahiro AKASHI


> 
> Thanks,
> 
> James

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