Re:[PATCH V4] riscv: kexec: Fixup synchronization problem between init_mm and active_mm

[xingxg2008 <xingxg2008@163.com>]

Tested-by: Xing Xiaoguang <xingxg2008@163.com>

The patch works fine on Linux 6.5-RC1 which runs on SOPHGO
SG2042 EVB that has 64 RISC-V cores.




At 2023-07-14 18:36:59, guoren@kernel.org wrote:
>From: Guo Ren <guoren@linux.alibaba.com>
>
>The machine_kexec() uses set_memory_x to modify the direct mapping
>attributes 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. Because the control code buffer was moved from the
>direct mapping area to the vmalloc location, we need an additional
>va_va_offset to fix up va_pa_offset.
>
>Fixes: 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")
>Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
>Reported-by: Xing XiaoGuang <xingxg2008@163.com>
>Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
>Signed-off-by: Guo Ren <guoren@kernel.org>
>---
>Changelog:
>V4:
> - Fixup va_pa_offset with additional va_va_offset.
> - Add Reported-by tag.
>
>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 | 18 +++++++++++++++---
> 2 files changed, 16 insertions(+), 3 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..60c1ef3c2232 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 +220,10 @@ 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;
>+	unsigned long va_va_offset =
>+			(unsigned long) page_address(image->control_code_page)
>+		      - (unsigned long) control_code_buffer;
> 	riscv_kexec_method kexec_method = NULL;
> 
> #ifdef CONFIG_SMP
>@@ -234,6 +246,6 @@ machine_kexec(struct kimage *image)
> 	/* Jump to the relocation code */
> 	pr_notice("Bye...\n");
> 	kexec_method(first_ind_entry, jump_addr, fdt_addr,
>-		     this_hart_id, kernel_map.va_pa_offset);
>+		     this_hart_id, kernel_map.va_pa_offset - va_va_offset);
> 	unreachable();
> }
>-- 
>2.36.1