Re: [PATCH] riscv: mm: Add proper handling for HWPOISON faults

[Ruidong Tian <tianruidong@linux.alibaba.com>]

Gentle reminder on this patch. Thanks.

> From: winterddd <tianruidong@linux.alibaba.com>
>
> Currently, the RISC-V fault handler treats memory poisoning faults
> (VM_FAULT_HWPOISON and VM_FAULT_HWPOISON_LARGE) as a generic bus error
> (BUS_ADRERR). This is incorrect as it loses crucial information about
> the nature of the error.
>
> As for describe in [0], A SIGBUS is sent with the correct machine check
> error code (BUS_MCEERR_AR) and populates `si_addr_lsb`(log2 of the
> corruption page size) in siginfo while there is page fault with poison
> page.
>
> The logic is based on the existing arm64 implementation for handling
> HWPOISON.
>
> Testing
> --------------
> ras-tools[0] is used to test.
>
> ./einj_mem_uc -j -k single &
>
> echo 0x107943b400 > /sys/devices/system/memory/hard_offline_page
>
> echo trigger > ./trigger_start
>
> before apply this patch:
> 	signal 7 code 2 addr 0x7fff95bdc400
> after apply this patch:
> 	signal 7 code 4 addr 0x7fff95bdc400
>
> [0]: https://www.man7.org/linux/man-pages/man2/sigaction.2.html
> [1]: https://kernel.googlesource.com/pub/scm/linux/kernel/git/aegl/ras-tools/
>
> Signed-off-by: Ruidong Tian <tianruidong@linux.alibaba.com>
> ---
>   arch/riscv/include/asm/bug.h |  1 +
>   arch/riscv/kernel/traps.c    | 32 ++++++++++++++++++++++----------
>   arch/riscv/mm/fault.c        | 12 +++++++++++-
>   3 files changed, 34 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/include/asm/bug.h b/arch/riscv/include/asm/bug.h
> index 4c03e20ad11f..23711f2ffae3 100644
> --- a/arch/riscv/include/asm/bug.h
> +++ b/arch/riscv/include/asm/bug.h
> @@ -95,5 +95,6 @@ struct task_struct;
>   void __show_regs(struct pt_regs *regs);
>   void die(struct pt_regs *regs, const char *str);
>   void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr);
> +void riscv_force_sig_mceerr(int code, unsigned long addr, short lsb);
>   
>   #endif /* _ASM_RISCV_BUG_H */
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index d46347482509..17dad6f8d678 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -113,20 +113,32 @@ void die(struct pt_regs *regs, const char *str)
>   		make_task_dead(SIGSEGV);
>   }
>   
> -void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
> +static void riscv_show_signal(int signo, int code, unsigned long addr)
>   {
>   	struct task_struct *tsk = current;
> +	struct pt_regs *regs = task_pt_regs(tsk);
>   
> -	if (show_unhandled_signals && unhandled_signal(tsk, signo)
> -	    && printk_ratelimit()) {
> -		pr_info("%s[%d]: unhandled signal %d code 0x%x at 0x" REG_FMT,
> -			tsk->comm, task_pid_nr(tsk), signo, code, addr);
> -		print_vma_addr(KERN_CONT " in ", instruction_pointer(regs));
> -		pr_cont("\n");
> -		__show_regs(regs);
> -		dump_instr(KERN_INFO, regs);
> -	}
> +	if (!show_unhandled_signals || !unhandled_signal(tsk, signo)
> +	    || !printk_ratelimit())
> +		return;
> +
> +	pr_info("%s[%d]: unhandled signal %d code 0x%x at 0x" REG_FMT,
> +		tsk->comm, task_pid_nr(tsk), signo, code, addr);
> +	print_vma_addr(KERN_CONT " in ", instruction_pointer(regs));
> +	pr_cont("\n");
> +	__show_regs(regs);
> +	dump_instr(KERN_INFO, regs);
> +}
>   
> +void riscv_force_sig_mceerr(int code, unsigned long addr, short lsb)
> +{
> +	riscv_show_signal(SIGBUS, code, addr);
> +	force_sig_mceerr(code, (void __user *)addr, lsb);
> +}
> +
> +void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
> +{
> +	riscv_show_signal(signo, code, addr);
>   	force_sig_fault(signo, code, (void __user *)addr);
>   }
>   
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 04ed6f8acae4..a6ccc4ab3a75 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -16,6 +16,7 @@
>   #include <linux/kprobes.h>
>   #include <linux/kfence.h>
>   #include <linux/entry-common.h>
> +#include <linux/hugetlb.h>
>   
>   #include <asm/ptrace.h>
>   #include <asm/tlbflush.h>
> @@ -128,10 +129,19 @@ static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_f
>   		 */
>   		pagefault_out_of_memory();
>   		return;
> -	} else if (fault & (VM_FAULT_SIGBUS | VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) {
> +	} else if (fault & VM_FAULT_SIGBUS) {
>   		/* Kernel mode? Handle exceptions or die */
>   		do_trap(regs, SIGBUS, BUS_ADRERR, addr);
>   		return;
> +	} else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) {
> +		unsigned int lsb;
> +
> +		lsb = PAGE_SHIFT;
> +		if (fault & VM_FAULT_HWPOISON_LARGE)
> +			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
> +
> +		riscv_force_sig_mceerr(BUS_MCEERR_AR, addr, lsb);
> +		return;
>   	} else if (fault & VM_FAULT_SIGSEGV) {
>   		do_trap(regs, SIGSEGV, SEGV_MAPERR, addr);
>   		return;