On Tue, Jan 17, 2017 at 05:20:44PM +0900, AKASHI Takahiro wrote:
> On Fri, Jan 13, 2017 at 11:39:15AM +0000, Mark Rutland wrote:
> > Great! I think it would be better to follow the approach of
> > mark_rodata_ro(), rather than opening up set_memory_*(), but otherwise,
> > it looks like it should work.
>
> I'm not quite sure what the approach of mark_rodata_ro() means, but
> I found that using create_mapping_late() may cause two problems:
>
> 1) it fails when PTE_CONT bits mismatch between an old and new mmu entry.
> This can happen, say, if the memory range for crash dump kernel
> starts in the mid of _continuous_ pages.
That should only happen if we try to remap a segment different to what
we originally mapped.
I was intending that we'd explicitly map the reserved region separately
in the boot path, like we do for kernel segments in map_kernel(). We
would allow sections and/or CONT entires.
Then, in __map_memblock() we'd then skip that range as we do for the
linear map alias of the kernel image.
That way, we can later use create_mapping_late for that same region, and
it should handle sections and/or CONT entries in the exact same way as
it does for the kernel image segments in mark_rodata_ro().
> 2) The control code page, of one-page size, is still written out in
> machine_kexec() which is called at a crash, and this means that
> the range must be writable even after kexec_load(), but
> create_mapping_late() does not handle a case of changing attributes
> for a single page which is in _section_ mapping.
> We cannot make single-page mapping for the control page since the address
> of that page is not determined at the boot time.
That is a problem. I'm not sure I follow how set_memory_*() helps here
though?
> As for (1), we need to call memblock_isolate_range() to make the region
> an independent one.
>
> > Either way, this still leaves us with an RO alias on crashed cores (and
> > potential cache attribute mismatches in future). Do we need to read from
> > the region later,
>
> I believe not, but the region must be _writable_ as I mentioned in (2) above.
> To avoid this issue, we have to move copying the control code page
> to machine_kexec_prepare() which is called in kexec_load() and so
> the region is writable anyway then.
> I want Geoff to affirm that this change is safe.
>
> (See my second solution below.)
>From a quick scan that looks ok.
> > or could we unmap it entirely?
>
> given the change above, I think we can.
Great!
> Is there any code to re-use especially for unmapping?
I don't think we have much code useful for unmapping. We could re-use
create_mapping_late for this, passing a set of prot bits that means the
entries are invalid (e.g. have a PAGE_KERNEL_INVALID).
We'd have to perform the TLB invalidation ourselves, but that shouldn't
be too painful.
Thanks,
Mark.
> ===8<===
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index c0fc3d458195..80a52e9aaf73 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -26,8 +26,6 @@
> extern const unsigned char arm64_relocate_new_kernel[];
> extern const unsigned long arm64_relocate_new_kernel_size;
>
> -static unsigned long kimage_start;
> -
> /**
> * kexec_image_info - For debugging output.
> */
> @@ -68,7 +66,7 @@ void machine_kexec_cleanup(struct kimage *kimage)
> */
> int machine_kexec_prepare(struct kimage *kimage)
> {
> - kimage_start = kimage->start;
> + void *reboot_code_buffer;
>
> kexec_image_info(kimage);
>
> @@ -77,6 +75,21 @@ int machine_kexec_prepare(struct kimage *kimage)
> return -EBUSY;
> }
>
> + reboot_code_buffer =
> + phys_to_virt(page_to_phys(kimage->control_code_page));
> +
> + /*
> + * Copy arm64_relocate_new_kernel to the reboot_code_buffer for use
> + * after the kernel is shut down.
> + */
> + memcpy(reboot_code_buffer, arm64_relocate_new_kernel,
> + arm64_relocate_new_kernel_size);
> +
> + /* Flush the reboot_code_buffer in preparation for its execution. */
> + __flush_dcache_area(reboot_code_buffer, arm64_relocate_new_kernel_size);
> + flush_icache_range((uintptr_t)reboot_code_buffer,
> + arm64_relocate_new_kernel_size);
> +
> return 0;
> }
>
> @@ -147,7 +160,6 @@ static void kexec_segment_flush(const struct kimage *kimage)
> void machine_kexec(struct kimage *kimage)
> {
> phys_addr_t reboot_code_buffer_phys;
> - void *reboot_code_buffer;
>
> /*
> * New cpus may have become stuck_in_kernel after we loaded the image.
> @@ -156,7 +168,6 @@ void machine_kexec(struct kimage *kimage)
> !WARN_ON(kimage == kexec_crash_image));
>
> reboot_code_buffer_phys = page_to_phys(kimage->control_code_page);
> - reboot_code_buffer = phys_to_virt(reboot_code_buffer_phys);
>
> kexec_image_info(kimage);
>
> @@ -164,26 +175,12 @@ void machine_kexec(struct kimage *kimage)
> kimage->control_code_page);
> pr_debug("%s:%d: reboot_code_buffer_phys: %pa\n", __func__, __LINE__,
> &reboot_code_buffer_phys);
> - pr_debug("%s:%d: reboot_code_buffer: %p\n", __func__, __LINE__,
> - reboot_code_buffer);
> pr_debug("%s:%d: relocate_new_kernel: %p\n", __func__, __LINE__,
> arm64_relocate_new_kernel);
> pr_debug("%s:%d: relocate_new_kernel_size: 0x%lx(%lu) bytes\n",
> __func__, __LINE__, arm64_relocate_new_kernel_size,
> arm64_relocate_new_kernel_size);
>
> - /*
> - * Copy arm64_relocate_new_kernel to the reboot_code_buffer for use
> - * after the kernel is shut down.
> - */
> - memcpy(reboot_code_buffer, arm64_relocate_new_kernel,
> - arm64_relocate_new_kernel_size);
> -
> - /* Flush the reboot_code_buffer in preparation for its execution. */
> - __flush_dcache_area(reboot_code_buffer, arm64_relocate_new_kernel_size);
> - flush_icache_range((uintptr_t)reboot_code_buffer,
> - arm64_relocate_new_kernel_size);
> -
> /* Flush the kimage list and its buffers. */
> kexec_list_flush(kimage);
>
> @@ -206,7 +203,7 @@ void machine_kexec(struct kimage *kimage)
> */
>
> cpu_soft_restart(kimage != kexec_crash_image,
> - reboot_code_buffer_phys, kimage->head, kimage_start, 0);
> + reboot_code_buffer_phys, kimage->head, kimage->start, 0);
>
> BUG(); /* Should never get here. */
> }
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 569ec3325bc8..e4cc170edc0c 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -90,6 +90,7 @@ early_param("initrd", early_initrd);
> static void __init reserve_crashkernel(void)
> {
> unsigned long long crash_size, crash_base;
> + int start_rgn, end_rgn;
> int ret;
>
> ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> @@ -120,6 +121,8 @@ static void __init reserve_crashkernel(void)
> return;
> }
> }
> + memblock_isolate_range(&memblock.memory, crash_base, crash_size,
> + &start_rgn, &end_rgn);
> memblock_reserve(crash_base, crash_size);
>
> pr_info("Reserving %lldMB of memory at %lldMB for crashkernel\n",
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 17243e43184e..b7c75845407a 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -22,6 +22,8 @@
> #include <linux/kernel.h>
> #include <linux/errno.h>
> #include <linux/init.h>
> +#include <linux/ioport.h>
> +#include <linux/kexec.h>
> #include <linux/libfdt.h>
> #include <linux/mman.h>
> #include <linux/nodemask.h>
> @@ -817,3 +819,27 @@ int pmd_clear_huge(pmd_t *pmd)
> pmd_clear(pmd);
> return 1;
> }
> +
> +#ifdef CONFIG_KEXEC_CORE
> +void arch_kexec_protect_crashkres(void)
> +{
> + flush_tlb_all();
> +
> + create_mapping_late(crashk_res.start, __phys_to_virt(crashk_res.start),
> + resource_size(&crashk_res), PAGE_KERNEL_RO);
> +
> + /* flush the TLBs after updating live kernel mappings */
> + flush_tlb_all();
> +}
> +
> +void arch_kexec_unprotect_crashkres(void)
> +{
> + flush_tlb_all();
> +
> + create_mapping_late(crashk_res.start, __phys_to_virt(crashk_res.start),
> + resource_size(&crashk_res), PAGE_KERNEL);
> +
> + /* flush the TLBs after updating live kernel mappings */
> + flush_tlb_all();
> +}
> +#endif
> ===>8===
