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

[AKASHI Takahiro]

James,

On Mon, May 07, 2018 at 02:59:07PM +0900, AKASHI Takahiro wrote:
> 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.

If you don't have further objection, I will take memblock approach
(with factoring out powerpc's arch_kexec_walk_mem()).

Thanks,
-Takahiro AKASHI


> > 
> > > 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@xxxxxxxxxx>
> > > + *
> > 
> > > + * 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