linux-kernel - Re: [PATCH -fixes v4 3/3] riscv: Save/restore envcfg CSR during CPU suspend

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Date: Wed, 28 Feb 2024 14:27:31 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Samuel Holland <samuel.holland@...ive.com>
Cc: Palmer Dabbelt <palmer@...belt.com>, linux-kernel@...r.kernel.org, 
	Conor Dooley <conor@...nel.org>, Alexandre Ghiti <alex@...ti.fr>, linux-riscv@...ts.infradead.org, 
	Stefan O'Rear <sorear@...tmail.com>, stable@...r.kernel.org
Subject: Re: [PATCH -fixes v4 3/3] riscv: Save/restore envcfg CSR during CPU
 suspend

On Tue, Feb 27, 2024 at 10:55:35PM -0800, Samuel Holland wrote:
> The value of the [ms]envcfg CSR is lost when entering a nonretentive
> idle state, so the CSR must be rewritten when resuming the CPU.
> 
> Cc: <stable@...r.kernel.org> # v6.7+
> Fixes: 43c16d51a19b ("RISC-V: Enable cbo.zero in usermode")
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
> 
> Changes in v4:
>  - Check for Xlinuxenvcfg instead of Zicboz
> 
> Changes in v3:
>  - Check for Zicboz instead of the privileged ISA version
> 
> Changes in v2:
>  - Check for privileged ISA v1.12 instead of the specific CSR
>  - Use riscv_has_extension_likely() instead of new ALTERNATIVE()s
> 
>  arch/riscv/include/asm/suspend.h | 1 +
>  arch/riscv/kernel/suspend.c      | 4 ++++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
> index 02f87867389a..491296a335d0 100644
> --- a/arch/riscv/include/asm/suspend.h
> +++ b/arch/riscv/include/asm/suspend.h
> @@ -14,6 +14,7 @@ struct suspend_context {
>  	struct pt_regs regs;
>  	/* Saved and restored by high-level functions */
>  	unsigned long scratch;
> +	unsigned long envcfg;
>  	unsigned long tvec;
>  	unsigned long ie;
>  #ifdef CONFIG_MMU
> diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
> index 239509367e42..299795341e8a 100644
> --- a/arch/riscv/kernel/suspend.c
> +++ b/arch/riscv/kernel/suspend.c
> @@ -15,6 +15,8 @@
>  void suspend_save_csrs(struct suspend_context *context)
>  {
>  	context->scratch = csr_read(CSR_SCRATCH);
> +	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_XLINUXENVCFG))
> +		context->envcfg = csr_read(CSR_ENVCFG);
>  	context->tvec = csr_read(CSR_TVEC);
>  	context->ie = csr_read(CSR_IE);
>  
> @@ -36,6 +38,8 @@ void suspend_save_csrs(struct suspend_context *context)
>  void suspend_restore_csrs(struct suspend_context *context)
>  {
>  	csr_write(CSR_SCRATCH, context->scratch);
> +	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_XLINUXENVCFG))
> +		csr_write(CSR_ENVCFG, context->envcfg);
>  	csr_write(CSR_TVEC, context->tvec);
>  	csr_write(CSR_IE, context->ie);
>  
> -- 
> 2.43.1
>

Picking _likely vs. _unlikely sometimes feels like flipping a coin, but
we'll presumably be increasing the likelihood of xlinuxenvcfg being
present as we add more and more envcfg using extensions, so maybe we
should use _likely here now, lest we forget to change it someday. But,
either way,

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>

Thanks,
drew