linux-kernel - Re: [PATCH] LoongArch: Save and restore CSR.CNTC for hibernation

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Message-ID: <7135de9f-4372-4e12-994d-ecdc234bff28@linux.dev>
Date: Thu, 15 May 2025 09:30:36 +0800
From: Yanteng Si <si.yanteng@...ux.dev>
To: Huacai Chen <chenhuacai@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, Xuefeng Li <lixuefeng@...ngson.cn>,
 Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
 Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, Xianglai Li <lixianglai@...ngson.cn>
Subject: Re: [PATCH] LoongArch: Save and restore CSR.CNTC for hibernation

在 5/14/25 10:46 PM, Huacai Chen 写道:
> Save and restore CSR.CNTC for hibernation which is similar to suspend.
> 
> For host this is unnecessary because sched clock is ensured continuous,
> but for kvm guest sched clock isn't enough because rdtime.d should also
> be continuous.
> 
> Host::rdtime.d = Host::CSR.CNTC + counter
> Guest::rdtime.d = Host::CSR.CNTC + Host::CSR.GCNTC + Guest::CSR.CNTC + counter
> 
> so,
> 
> Guest::rdtime.d = Host::rdtime.d + Host::CSR.GCNTC + Guest::CSR.CNTC
> 
> To ensure Guest::rdtime.d continuous, Host::rdtime.d should be at first
> continuous, while Host::CSR.GCNTC / Guest::CSR.CNTC is maintained by KVM.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Xianglai Li <lixianglai@...ngson.cn>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
Reviewed-by: Yanteng Si <si.yanteng@...ux.dev>

Thanks,
Yanteng
> ---
>   arch/loongarch/kernel/time.c     | 2 +-
>   arch/loongarch/power/hibernate.c | 3 +++
>   2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/loongarch/kernel/time.c b/arch/loongarch/kernel/time.c
> index e2d3bfeb6366..bc75a3a69fc8 100644
> --- a/arch/loongarch/kernel/time.c
> +++ b/arch/loongarch/kernel/time.c
> @@ -111,7 +111,7 @@ static unsigned long __init get_loops_per_jiffy(void)
>   	return lpj;
>   }
>   
> -static long init_offset __nosavedata;
> +static long init_offset;
>   
>   void save_counter(void)
>   {
> diff --git a/arch/loongarch/power/hibernate.c b/arch/loongarch/power/hibernate.c
> index 1e0590542f98..e7b7346592cb 100644
> --- a/arch/loongarch/power/hibernate.c
> +++ b/arch/loongarch/power/hibernate.c
> @@ -2,6 +2,7 @@
>   #include <asm/fpu.h>
>   #include <asm/loongson.h>
>   #include <asm/sections.h>
> +#include <asm/time.h>
>   #include <asm/tlbflush.h>
>   #include <linux/suspend.h>
>   
> @@ -14,6 +15,7 @@ struct pt_regs saved_regs;
>   
>   void save_processor_state(void)
>   {
> +	save_counter();
>   	saved_crmd = csr_read32(LOONGARCH_CSR_CRMD);
>   	saved_prmd = csr_read32(LOONGARCH_CSR_PRMD);
>   	saved_euen = csr_read32(LOONGARCH_CSR_EUEN);
> @@ -26,6 +28,7 @@ void save_processor_state(void)
>   
>   void restore_processor_state(void)
>   {
> +	sync_counter();
>   	csr_write32(saved_crmd, LOONGARCH_CSR_CRMD);
>   	csr_write32(saved_prmd, LOONGARCH_CSR_PRMD);
>   	csr_write32(saved_euen, LOONGARCH_CSR_EUEN);