On Tue, Sep 13, 2011 at 03:26:36PM +0200, Michael Holzheu wrote:
> From: Michael Holzheu <holzheu at linux.vnet.ibm.com>
>
> This patch introduces a mechanism that allows architecture backends to
> remove page tables for the crashkernel memory. This can protect the loaded
> kdump kernel from being overwritten by broken kernel code. Two new
> functions crash_map_reserved_pages() and crash_unmap_reserved_pages() are
> added that can be implemented by architecture code. The
> crash_map_reserved_pages() function is called before and
> crash_unmap_reserved_pages() after the crashkernel segments are loaded. The
> functions are also called in crash_shrink_memory() to create/remove page
> tables when the crashkernel memory size is reduced.
>
> To support architectures that have large pages this patch also introduces
> a new define KEXEC_CRASH_MEM_ALIGN. The crashkernel start and size must
> always be aligned with KEXEC_CRASH_MEM_ALIGN.
>
> Signed-off-by: Michael Holzheu <holzheu at linux.vnet.ibm.com>
Looks reasonable conceptually. Hence...
Acked-by: Vivek Goyal <vgoyal at redhat.com>
Thanks
Vivek
> ---
> include/linux/kexec.h | 6 ++++++
> kernel/kexec.c | 21 +++++++++++++++++++--
> 2 files changed, 25 insertions(+), 2 deletions(-)
>
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -37,6 +37,10 @@
> #define KEXEC_CRASH_CONTROL_MEMORY_LIMIT KEXEC_CONTROL_MEMORY_LIMIT
> #endif
>
> +#ifndef KEXEC_CRASH_MEM_ALIGN
> +#define KEXEC_CRASH_MEM_ALIGN PAGE_SIZE
> +#endif
> +
> #define KEXEC_NOTE_HEAD_BYTES ALIGN(sizeof(struct elf_note), 4)
> #define KEXEC_CORE_NOTE_NAME "CORE"
> #define KEXEC_CORE_NOTE_NAME_BYTES ALIGN(sizeof(KEXEC_CORE_NOTE_NAME), 4)
> @@ -133,6 +137,8 @@ extern void crash_kexec(struct pt_regs *
> int kexec_should_crash(struct task_struct *);
> void crash_save_cpu(struct pt_regs *regs, int cpu);
> void crash_save_vmcoreinfo(void);
> +void crash_map_reserved_pages(void);
> +void crash_unmap_reserved_pages(void);
> void arch_crash_save_vmcoreinfo(void);
> void vmcoreinfo_append_str(const char *fmt, ...)
> __attribute__ ((format (printf, 1, 2)));
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -999,6 +999,7 @@ SYSCALL_DEFINE4(kexec_load, unsigned lon
> kimage_free(xchg(&kexec_crash_image, NULL));
> result = kimage_crash_alloc(&image, entry,
> nr_segments, segments);
> + crash_map_reserved_pages();
> }
> if (result)
> goto out;
> @@ -1015,6 +1016,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned lon
> goto out;
> }
> kimage_terminate(image);
> + if (flags & KEXEC_ON_CRASH)
> + crash_unmap_reserved_pages();
> }
> /* Install the new kernel, and Uninstall the old */
> image = xchg(dest_image, image);
> @@ -1026,6 +1029,18 @@ out:
> return result;
> }
>
> +/*
> + * Add and remove page tables for crashkernel memory
> + *
> + * Provide an empty default implementation here -- architecture
> + * code may override this
> + */
> +void __weak crash_map_reserved_pages(void)
> +{}
> +
> +void __weak crash_unmap_reserved_pages(void)
> +{}
> +
> #ifdef CONFIG_COMPAT
> asmlinkage long compat_sys_kexec_load(unsigned long entry,
> unsigned long nr_segments,
> @@ -1134,14 +1149,16 @@ int crash_shrink_memory(unsigned long ne
> goto unlock;
> }
>
> - start = roundup(start, PAGE_SIZE);
> - end = roundup(start + new_size, PAGE_SIZE);
> + start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
> + end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);
>
> + crash_map_reserved_pages();
> crash_free_reserved_phys_range(end, crashk_res.end);
>
> if ((start == end) && (crashk_res.parent != NULL))
> release_resource(&crashk_res);
> crashk_res.end = end - 1;
> + crash_unmap_reserved_pages();
>
> unlock:
> mutex_unlock(&kexec_mutex);
