linux-kernel - Re: [PATCH] LoongArch: Ensure FP/SIMD registers in the core dump file is up to date

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Message-ID: <0b509186-bf01-2151-0954-d669075c1f71@xen0n.name>
Date:   Sat, 26 Aug 2023 15:52:35 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-arch@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Ensure FP/SIMD registers in the core dump file
 is up to date

On 8/25/23 19:42, Huacai Chen wrote:
> This is a port of commit 379eb01c21795edb4c ("riscv: Ensure the value
> of FP registers in the core dump file is up to date").
>
> The values of FP/SIMD registers in the core dump file come from the
> thread.fpu. However, kernel saves the FP/SIMD registers only before
> scheduling out the process. If no process switch happens during the
> exception handling, kernel will not have a chance to save the latest
> values of FP/SIMD registers. So it may cause their values in the core
> dump file incorrect. To solve this problem, force fpr_get()/simd_get()
> to save the FP/SIMD registers into the thread.fpu if the target task
> equals the current task.
>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>   arch/loongarch/include/asm/fpu.h | 22 ++++++++++++++++++----
>   arch/loongarch/kernel/ptrace.c   |  4 ++++
>   2 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/fpu.h b/arch/loongarch/include/asm/fpu.h
> index b541f6248837..08a45e9fd15c 100644
> --- a/arch/loongarch/include/asm/fpu.h
> +++ b/arch/loongarch/include/asm/fpu.h
> @@ -173,16 +173,30 @@ static inline void restore_fp(struct task_struct *tsk)
>   		_restore_fp(&tsk->thread.fpu);
>   }
>   
> -static inline union fpureg *get_fpu_regs(struct task_struct *tsk)
> +static inline void get_fpu_regs(struct task_struct *tsk)
Removing the return value from the signature means the function is no 
longer a getter, so maybe the name should get changed as well? Like 
"save_fpu_regs"?
>   {
> +	unsigned int euen;
> +
>   	if (tsk == current) {
>   		preempt_disable();
> -		if (is_fpu_owner())
> +
> +		euen = csr_read32(LOONGARCH_CSR_EUEN);
> +
> +#ifdef CONFIG_CPU_HAS_LASX
> +		if (euen & CSR_EUEN_LASXEN)
> +			_save_lasx(&current->thread.fpu);
> +		else
> +#endif
> +#ifdef CONFIG_CPU_HAS_LSX
> +		if (euen & CSR_EUEN_LSXEN)
> +			_save_lsx(&current->thread.fpu);
> +		else
> +#endif
> +		if (euen & CSR_EUEN_FPEN)
>   			_save_fp(&current->thread.fpu);
> +
>   		preempt_enable();
>   	}
> -
> -	return tsk->thread.fpu.fpr;
>   }
>   
>   static inline int is_simd_owner(void)
> diff --git a/arch/loongarch/kernel/ptrace.c b/arch/loongarch/kernel/ptrace.c
> index 2bb5ec55ae1e..209e3d29e0b2 100644
> --- a/arch/loongarch/kernel/ptrace.c
> +++ b/arch/loongarch/kernel/ptrace.c
> @@ -148,6 +148,8 @@ static int fpr_get(struct task_struct *target,
>   {
>   	int r;
>   
> +	get_fpu_regs(target);
> +
>   	if (sizeof(target->thread.fpu.fpr[0]) == sizeof(elf_fpreg_t))
>   		r = gfpr_get(target, &to);
>   	else
> @@ -279,6 +281,8 @@ static int simd_get(struct task_struct *target,
>   {
>   	const unsigned int wr_size = NUM_FPU_REGS * regset->size;
>   
> +	get_fpu_regs(target);
> +
>   	if (!tsk_used_math(target)) {
>   		/* The task hasn't used FP or LSX, fill with 0xff */
>   		copy_pad_fprs(target, regset, &to, 0);

Otherwise this should be fine. (I don't know why that helper is 
previously unused though...)

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/