Date:	Mon, 12 Oct 2015 21:08:57 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Chen Yu <yu.c.chen@...el.com>
Cc:	mingo@...hat.com, pavel@....cz, bp@...e.de, tglx@...utronix.de,
	hpa@...or.com, rui.zhang@...el.com, luto@...nel.org,
	linux@...izon.com, dsmythies@...us.net, linux-pm@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	marcin.kaszewski@...el.com
Subject: Re: [PATCH][v5] x86, suspend: Save/restore extra MSR registers for suspend

On Sunday, October 11, 2015 11:20:01 AM Chen Yu wrote:
> A bug is reported(https://bugzilla.redhat.com/show_bug.cgi?id=1227208)
> that, after resumed from S3, CPU is running at a low speed.
> After investigation, it is found that, BIOS has modified the value
> of THERM_CONTROL register during S3, and changes it from 0 to 0x10
> (thus changes the clock modulation from reserved to enabled),
> since value of 0x10 means CPU can only get 25% of the Duty Cycle,
> this triggers the problem.
> 
> Here is a simple scenario to reproduce the issue(only for above case):
> 1.Boot up the system
> 2.Get MSR with address 0x19a, it should be 0
> 3.Put the system into sleep, then wake it up
> 4.Get MSR with address 0x19a, it should be 0(actually it shows 0x10)
> 
> Although this is a BIOS issue, it would be more robust for linux to deal
> with this situation. This patch fixes this issue by introducing a framework
> to save/restore specified MSR registers(THERM_CONTROL in this case)
> for suspend/resume.
> 
> When user encounters a problematic platform and needs to protect the
> MSRs during suspending, he can simply add a quirk entry in
> msr_save_dmi_table, and customizes MSR registers inside the quirk
> callback, for example:
> 
> u32 msr_id_need_to_save[] = {MSR_ID0, MSR_ID1, MSR_ID2...};
> 
> and the quirk mechanism ensures that, once resumed from suspended,
> the MSRs indicated by these IDs will be restored to their original values
> before suspended.
> 
> Since both 64/32-bit kernels are affected, this patch covers 64/32-bit
> common code path. And because the MSRs specified by the user might not
> be available or readable in any situation, we use rdmsrl_safe to safely
> save these MSRs.
> 
> Tested-by: Marcin Kaszewski <marcin.kaszewski@...el.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
> v5:
>  - Rename some structures and variables for better understanding.
>    Put the defination of struct saved_msr and struct msr_save_data to
>    header: arch/x86/include/asm/msr.h.
>    Re-implement the msr_save_context and msr_restore_context for better
>    maintaining.
>    Convert the msr_context_array to be dynamically allocated.
>    Fix some typos in code comments.
> v4:
>  - Revert v3 to v2, and fix some typos in changelog/comments. 
>    Use msr_info structure instead of msr_id + msr_value.
>    Adjust some codes for better readability.
> v3:
>  - Simplify the patch to only focus on THERM_CONTROL register.
>    This will make things 'just work'.
> v2:
>  - Cover both 64/32-bit common code path.
>    Use rdmsrl_safe to safely read MSR.
>    Introduce a quirk framework for save/restore specified MSR on different
>    platforms.
> ---
>  arch/x86/include/asm/msr.h        | 10 ++++
>  arch/x86/include/asm/suspend_32.h |  1 +
>  arch/x86/include/asm/suspend_64.h |  1 +
>  arch/x86/power/cpu.c              | 98 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 110 insertions(+)
> 
> diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
> index 77d8b28..5ae24ed 100644
> --- a/arch/x86/include/asm/msr.h
> +++ b/arch/x86/include/asm/msr.h
> @@ -32,6 +32,16 @@ struct msr_regs_info {
>  	int err;
>  };
>  
> +struct msr_save_data {
> +	bool msr_saved;
> +	struct msr_info rv;
> +};
> +
> +struct msr_context {
> +	unsigned short num;
> +	struct msr_save_data *msr_array;
> +};
> +
>  static inline unsigned long long native_read_tscp(unsigned int *aux)
>  {
>  	unsigned long low, high;
> diff --git a/arch/x86/include/asm/suspend_32.h b/arch/x86/include/asm/suspend_32.h
> index d1793f0..5057f65 100644
> --- a/arch/x86/include/asm/suspend_32.h
> +++ b/arch/x86/include/asm/suspend_32.h
> @@ -15,6 +15,7 @@ struct saved_context {
>  	unsigned long cr0, cr2, cr3, cr4;
>  	u64 misc_enable;
>  	bool misc_enable_saved;
> +	struct msr_context msr_to_save;
>  	struct desc_ptr gdt_desc;
>  	struct desc_ptr idt;
>  	u16 ldt;
> diff --git a/arch/x86/include/asm/suspend_64.h b/arch/x86/include/asm/suspend_64.h
> index 7ebf0eb..60941de 100644
> --- a/arch/x86/include/asm/suspend_64.h
> +++ b/arch/x86/include/asm/suspend_64.h
> @@ -24,6 +24,7 @@ struct saved_context {
>  	unsigned long cr0, cr2, cr3, cr4, cr8;
>  	u64 misc_enable;
>  	bool misc_enable_saved;
> +	struct msr_context msr_to_save;
>  	unsigned long efer;
>  	u16 gdt_pad; /* Unused */
>  	struct desc_ptr gdt_desc;
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index 9ab5279..fd3243a 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -23,6 +23,7 @@
>  #include <asm/debugreg.h>
>  #include <asm/cpu.h>
>  #include <asm/mmu_context.h>
> +#include <linux/dmi.h>
>  
>  #ifdef CONFIG_X86_32
>  __visible unsigned long saved_context_ebx;
> @@ -32,6 +33,29 @@ __visible unsigned long saved_context_eflags;
>  #endif
>  struct saved_context saved_context;
>  
> +static void msr_save_context(struct saved_context *ctxt)
> +{
> +	struct msr_save_data *msr = ctxt->msr_to_save.msr_array;
> +	struct msr_save_data *end = msr + ctxt->msr_to_save.num;
> +
> +	while (msr < end) {
> +		msr->msr_saved = !rdmsrl_safe(msr->rv.msr_no, &msr->rv.reg.q);
> +		msr++;
> +	}
> +}
> +
> +static void msr_restore_context(struct saved_context *ctxt)
> +{
> +	struct msr_save_data *msr = ctxt->msr_to_save.msr_array;
> +	struct msr_save_data *end = msr + ctxt->msr_to_save.num;
> +
> +	while (msr < end) {
> +		if (msr->msr_saved)
> +			wrmsrl(msr->rv.msr_no, msr->rv.reg.q);
> +		msr++;
> +	}
> +}
> +
>  /**
>   *	__save_processor_state - save CPU registers before creating a
>   *		hibernation image and before restoring the memory state from it
> @@ -111,6 +135,7 @@ static void __save_processor_state(struct saved_context *ctxt)
>  #endif
>  	ctxt->misc_enable_saved = !rdmsrl_safe(MSR_IA32_MISC_ENABLE,
>  					       &ctxt->misc_enable);
> +	msr_save_context(ctxt);
>  }
>  
>  /* Needed by apm.c */
> @@ -229,6 +254,7 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
>  	x86_platform.restore_sched_clock_state();
>  	mtrr_bp_restore();
>  	perf_restore_debug_store();
> +	msr_restore_context(ctxt);
>  }
>  
>  /* Needed by apm.c */
> @@ -320,3 +346,75 @@ static int __init bsp_pm_check_init(void)
>  }
>  
>  core_initcall(bsp_pm_check_init);
> +
> +/*
> + * The following section is a quirk framework for problematic BIOS:
> + * Sometimes MSRs are modified by BIOS after suspended to
> + * RAM, this might cause unexpected behavior after wakeup.
> + * Thus we save/restore these specified MSRs during suspending
> + * in order to work around it.
> + * A typical bug is reported at:
> + * https://bugzilla.redhat.com/show_bug.cgi?id=1227208
> + */
> +static int msr_init_context(const u32 *msr_id, const int total_num)
> +{
> +	int i = 0;
> +	struct msr_save_data *msr_data = NULL;
> +
> +	if (saved_context.msr_to_save.msr_array ||
> +			saved_context.msr_to_save.num > 0) {
> +		pr_err("PM: quirk already applied, please check your dmi match table.\n");
> +		return -EINVAL;
> +	}
> +
> +	msr_data = kmalloc_array(total_num,
> +			sizeof(struct msr_save_data), GFP_KERNEL);
> +	if (!msr_data) {
> +		pr_err("PM: can not allocate memory to save/restore MSRs during suspend.\n");
> +		return -ENOMEM;
> +	}
> +
> +	for (i = 0; i < total_num; i++) {
> +		msr_data[i].rv.msr_no = msr_id[i];
> +		msr_data[i].msr_saved = false;
> +		msr_data[i].rv.reg.q = 0;
> +	}
> +	saved_context.msr_to_save.num = total_num;
> +	saved_context.msr_to_save.msr_array = msr_data;
> +	return 0;
> +}
> +
> +/*
> + * For any further problematic BIOS/platforms,
> + * please add your own function similar to msr_initialize_bdw.
> + */
> +static int msr_initialize_bdw(const struct dmi_system_id *d)
> +{
> +	/* Add any extra MSR ids into this array. */
> +	u32 bdw_msr_id[] = {MSR_IA32_THERM_CONTROL};
> +
> +	pr_info("PM: %s detected, MSR saving is needed during suspending.\n",
> +		d->ident);
> +	return msr_init_context(bdw_msr_id, ARRAY_SIZE(bdw_msr_id));
> +}
> +
> +static struct dmi_system_id msr_save_dmi_table[] = {
> +	{
> +	 .callback = msr_initialize_bdw,
> +	 .ident = "BROADWELL BDX_EP",
> +	 .matches = {
> +		DMI_MATCH(DMI_SYS_VENDOR, "Intel Corporation"),
> +		DMI_MATCH(DMI_PRODUCT_NAME, "GRANTLEY"),
> +		DMI_MATCH(DMI_PRODUCT_VERSION, "E63448-400"),
> +		},
> +	},
> +	{}
> +};
> +
> +static int pm_check_save_msr(void)
> +{
> +	dmi_check_system(msr_save_dmi_table);
> +	return 0;
> +}
> +
> +late_initcall(pm_check_save_msr);
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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