Re: [PATCH v1 3/4] memblock: add MEMBLOCK_DRIVER_MANAGED to mimic IORESOURCE_SYSRAM_DRIVER_MANAGED

Mike Rapoport
2021-09-29T16:39:58Z

Hi,

On Mon, Sep 27, 2021 at 05:05:17PM +0200, David Hildenbrand wrote:
> Let's add a flag that corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED.
> Similar to MEMBLOCK_HOTPLUG, most infrastructure has to treat such memory
> like ordinary MEMBLOCK_NONE memory -- for example, when selecting memory
> regions to add to the vmcore for dumping in the crashkernel via
> for_each_mem_range().

Can you please elaborate on the difference in semantics of MEMBLOCK_HOTPLUG
and MEMBLOCK_DRIVER_MANAGED?
Unless I'm missing something they both mark memory that can be unplugged
anytime and so it should not be used in certain cases. Why is there a need
for a new flag?

> However, especially kexec_file is not supposed to select such memblocks via
> for_each_free_mem_range() / for_each_free_mem_range_reverse() to place
> kexec images, similar to how we handle IORESOURCE_SYSRAM_DRIVER_MANAGED
> without CONFIG_ARCH_KEEP_MEMBLOCK.
>
> Let's document why kexec_walk_memblock() won't try placing images on
> areas marked MEMBLOCK_DRIVER_MANAGED -- similar to
> IORESOURCE_SYSRAM_DRIVER_MANAGED handling in locate_mem_hole_callback()
> via kexec_walk_resources().
>
> We'll make sure that memory hotplug code sets the flag where applicable
> (IORESOURCE_SYSRAM_DRIVER_MANAGED) next. This prepares architectures
> that need CONFIG_ARCH_KEEP_MEMBLOCK, such as arm64, for virtio-mem
> support.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> include/linux/memblock.h | 16 ++++++++++++++--
> kernel/kexec_file.c | 5 +++++
> mm/memblock.c | 4 ++++
> 3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index b49a58f621bc..7d8d656d5082 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -33,12 +33,17 @@ extern unsigned long long max_possible_pfn;
> * @MEMBLOCK_NOMAP: don't add to kernel direct mapping and treat as
> * reserved in the memory map; refer to memblock_mark_nomap() description
> * for further details
> + * @MEMBLOCK_DRIVER_MANAGED: memory region that is always detected via a driver,
> + * corresponding to IORESOURCE_SYSRAM_DRIVER_MANAGED in the kernel resource
> + * tree. Especially kexec should never use this memory for placing images and
> + * shouldn't expose this memory to the second kernel.
> */
> enum memblock_flags {
> MEMBLOCK_NONE = 0x0, /* No special request */
> MEMBLOCK_HOTPLUG = 0x1, /* hotpluggable region */
> MEMBLOCK_MIRROR = 0x2, /* mirrored region */
> MEMBLOCK_NOMAP = 0x4, /* don't add to kernel direct mapping */
> + MEMBLOCK_DRIVER_MANAGED = 0x8, /* always detected via a driver */
> };
>
> /**
> @@ -209,7 +214,8 @@ static inline void __next_physmem_range(u64 *idx, struct memblock_type *type,
> */
> #define for_each_mem_range(i, p_start, p_end) \
> __for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE, \
> - MEMBLOCK_HOTPLUG, p_start, p_end, NULL)
> + MEMBLOCK_HOTPLUG | MEMBLOCK_DRIVER_MANAGED, \
> + p_start, p_end, NULL)
>
> /**
> * for_each_mem_range_rev - reverse iterate through memblock areas from
> @@ -220,7 +226,8 @@ static inline void __next_physmem_range(u64 *idx, struct memblock_type *type,
> */
> #define for_each_mem_range_rev(i, p_start, p_end) \
> __for_each_mem_range_rev(i, &memblock.memory, NULL, NUMA_NO_NODE, \
> - MEMBLOCK_HOTPLUG, p_start, p_end, NULL)
> + MEMBLOCK_HOTPLUG | MEMBLOCK_DRIVER_MANAGED,\
> + p_start, p_end, NULL)
>
> /**
> * for_each_reserved_mem_range - iterate over all reserved memblock areas
> @@ -250,6 +257,11 @@ static inline bool memblock_is_nomap(struct memblock_region *m)
> return m->flags & MEMBLOCK_NOMAP;
> }
>
> +static inline bool memblock_is_driver_managed(struct memblock_region *m)
> +{
> + return m->flags & MEMBLOCK_DRIVER_MANAGED;
> +}
> +
> int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
> unsigned long *end_pfn);
> void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 33400ff051a8..8347fc158d2b 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -556,6 +556,11 @@ static int kexec_walk_memblock(struct kexec_buf *kbuf,
> if (kbuf->image->type == KEXEC_TYPE_CRASH)
> return func(&crashk_res, kbuf);
>
> + /*
> + * Using MEMBLOCK_NONE will properly skip MEMBLOCK_DRIVER_MANAGED. See
> + * IORESOURCE_SYSRAM_DRIVER_MANAGED handling in
> + * locate_mem_hole_callback().
> + */
> if (kbuf->top_down) {
> for_each_free_mem_range_reverse(i, NUMA_NO_NODE, MEMBLOCK_NONE,
> &mstart, &mend, NULL) {
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 47a56b223141..540a35317fb0 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -979,6 +979,10 @@ static bool should_skip_region(struct memblock_type *type,
> if (!(flags & MEMBLOCK_NOMAP) && memblock_is_nomap(m))
> return true;
>
> + /* skip driver-managed memory unless we were asked for it explicitly */
> + if (!(flags & MEMBLOCK_DRIVER_MANAGED) && memblock_is_driver_managed(m))
> + return true;
> +
> return false;
> }
>
> --
> 2.31.1
>

--
Sincerely yours,
Mike.