Re: [PATCH V3] riscv: kexec: Fixup synchronization problem between init_mm and active_mm

[Guo Ren]

Sorry, this patch is broken with riscv_kexec_relocate which depends on
direct mapping. I'm debugging on it. Please abandon it.

On Thu, Jul 13, 2023 at 11:08 AM <guoren@xxxxxxxxxx> wrote:
>
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> The machine_kexec() uses set_memory_x to modify the direct mapping
> Aattributes from RW to RWX. The current implementation of set_memory_x

> does not split hugepages in the linear mapping and then when a PGD
> mapping is used, the whole PGD is marked as executable. But changing
> the permissions at the PGD level must be propagated to all the page
> tables. When kexec jumps into control_buffer, the instruction page
> fault happens, and there is no minor_pagefault for it, then panic.
>
> The bug is found on an MMU_sv39 machine, and the direct mapping used a
> 1GB PUD, the pgd entries. Here is the bug output:
>
>  kexec_core: Starting new kernel
>  Will call new kernel at 00300000 from hart id 0
>  FDT image at 747c7000
>  Bye...
>  Unable to handle kernel paging request at virtual address ffffffda23b0d000
>  Oops [#1]
>  Modules linked in:
>  CPU: 0 PID: 53 Comm: uinit Not tainted 6.4.0-rc6 #15
>  Hardware name: Sophgo Mango (DT)
>  epc : 0xffffffda23b0d000
>   ra : machine_kexec+0xa6/0xb0
>  epc : ffffffda23b0d000 ra : ffffffff80008272 sp : ffffffc80c173d10
>   gp : ffffffff8150e1e0 tp : ffffffd9073d2c40 t0 : 0000000000000000
>   t1 : 0000000000000042 t2 : 6567616d69205444 s0 : ffffffc80c173d50
>   s1 : ffffffd9076c4800 a0 : ffffffd9076c4800 a1 : 0000000000300000
>   a2 : 00000000747c7000 a3 : 0000000000000000 a4 : ffffffd800000000
>   a5 : 0000000000000000 a6 : ffffffd903619c40 a7 : ffffffffffffffff
>   s2 : ffffffda23b0d000 s3 : 0000000000300000 s4 : 00000000747c7000
>   s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
>   s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000000000000000
>   s11: 0000003f940001a0 t3 : ffffffff815351af t4 : ffffffff815351af
>   t5 : ffffffff815351b0 t6 : ffffffc80c173b50
>  status: 0000000200000100 badaddr: ffffffda23b0d000 cause: 000000000000000c
>
> Given the current flaw in the set_memory_x implementation, the simplest
> solution is to fix machine_kexec() to remap control code page outside
> the linear mapping.
>
> Fixes: 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")
> Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> ---
> Changelog:
> V3:
>  - Resume set_memory_x to set the _PAGE_EXEC attribute
>  - Optimize the commit log with Alexandre advice
>
> V2:
>  - Use vm_map_ram instead of modifying set_memory_x
>  - Correct Fixes tag
> ---
>  arch/riscv/include/asm/kexec.h    |  1 +
>  arch/riscv/kernel/machine_kexec.c | 13 +++++++++++--
>  2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kexec.h b/arch/riscv/include/asm/kexec.h
> index 2b56769cb530..17456e91476e 100644
> --- a/arch/riscv/include/asm/kexec.h
> +++ b/arch/riscv/include/asm/kexec.h
> @@ -41,6 +41,7 @@ crash_setup_regs(struct pt_regs *newregs,
>  struct kimage_arch {
>         void *fdt; /* For CONFIG_KEXEC_FILE */
>         unsigned long fdt_addr;
> +       void *control_code_buffer;
>  };
>
>  extern const unsigned char riscv_kexec_relocate[];
> diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
> index 2d139b724bc8..83b499178902 100644
> --- a/arch/riscv/kernel/machine_kexec.c
> +++ b/arch/riscv/kernel/machine_kexec.c
> @@ -86,7 +86,14 @@ machine_kexec_prepare(struct kimage *image)
>
>         /* Copy the assembler code for relocation to the control page */
>         if (image->type != KEXEC_TYPE_CRASH) {
> -               control_code_buffer = page_address(image->control_code_page);
> +               control_code_buffer = vm_map_ram(&image->control_code_page,
> +                                                KEXEC_CONTROL_PAGE_SIZE/PAGE_SIZE,
> +                                                NUMA_NO_NODE);
> +               if (control_code_buffer == NULL) {
> +                       pr_err("Failed to vm_map control page\n");
> +                       return -ENOMEM;
> +               }
> +
>                 control_code_buffer_sz = page_size(image->control_code_page);
>
>                 if (unlikely(riscv_kexec_relocate_size > control_code_buffer_sz)) {
> @@ -99,6 +106,8 @@ machine_kexec_prepare(struct kimage *image)
>
>                 /* Mark the control page executable */
>                 set_memory_x((unsigned long) control_code_buffer, 1);
> +
> +               internal->control_code_buffer = control_code_buffer;
>         }
>
>         return 0;
> @@ -211,7 +220,7 @@ machine_kexec(struct kimage *image)
>         unsigned long this_cpu_id = __smp_processor_id();
>         unsigned long this_hart_id = cpuid_to_hartid_map(this_cpu_id);
>         unsigned long fdt_addr = internal->fdt_addr;
> -       void *control_code_buffer = page_address(image->control_code_page);
> +       void *control_code_buffer = internal->control_code_buffer;
>         riscv_kexec_method kexec_method = NULL;
>
>  #ifdef CONFIG_SMP
> --
> 2.36.1
>


--
Best Regards
 Guo Ren