cpufreq: amd-pstate: avoid uninitialized variable use

  From: Arnd Bergmann <arnd@arndb.de>

The new epp support causes warnings about three separate
but related bugs:

1) failing before allocation should just return an error:

drivers/cpufreq/amd-pstate.c:951:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (!dev)
            ^~~~
drivers/cpufreq/amd-pstate.c:1018:9: note: uninitialized use occurs here
        return ret;
               ^~~

2) wrong variable to store return code:

drivers/cpufreq/amd-pstate.c:963:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (rc)
            ^~
drivers/cpufreq/amd-pstate.c:1019:9: note: uninitialized use occurs here
        return ret;
               ^~~
drivers/cpufreq/amd-pstate.c:963:2: note: remove the 'if' if its condition is always false
        if (rc)
        ^~~~~~~

3) calling amd_pstate_set_epp() in cleanup path after determining
that it should not be called:

drivers/cpufreq/amd-pstate.c:1055:6: error: variable 'epp' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (cpudata->epp_policy == cpudata->policy)
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/cpufreq/amd-pstate.c:1080:30: note: uninitialized use occurs here
        amd_pstate_set_epp(cpudata, epp);
                                    ^~~

All three are trivial to fix, but most likely there are additional bugs
in this function when the error handling was not really tested.

Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/cpufreq/amd-pstate.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
  

On 07 Feb 17:12, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The new epp support causes warnings about three separate
> but related bugs:
> 
> 1) failing before allocation should just return an error:
> 
> drivers/cpufreq/amd-pstate.c:951:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (!dev)
>             ^~~~
> drivers/cpufreq/amd-pstate.c:1018:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> 
> 2) wrong variable to store return code:
> 
> drivers/cpufreq/amd-pstate.c:963:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (rc)
>             ^~
> drivers/cpufreq/amd-pstate.c:1019:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> drivers/cpufreq/amd-pstate.c:963:2: note: remove the 'if' if its condition is always false
>         if (rc)
>         ^~~~~~~
> 
> 3) calling amd_pstate_set_epp() in cleanup path after determining
> that it should not be called:
> 
> drivers/cpufreq/amd-pstate.c:1055:6: error: variable 'epp' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (cpudata->epp_policy == cpudata->policy)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/cpufreq/amd-pstate.c:1080:30: note: uninitialized use occurs here
>         amd_pstate_set_epp(cpudata, epp);
>                                     ^~~
> 
> All three are trivial to fix, but most likely there are additional bugs
> in this function when the error handling was not really tested.
> 
> Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/cpufreq/amd-pstate.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 168a28bed6ee..847f5f31396d 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -940,7 +940,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
>  	struct amd_cpudata *cpudata;
>  	struct device *dev;
> -	int rc;
>  	u64 value;
>  
>  	/*
> @@ -950,7 +949,7 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	amd_perf_ctl_reset(policy->cpu);
>  	dev = get_cpu_device(policy->cpu);
>  	if (!dev)
> -		goto free_cpudata1;
> +		return -ENODEV;
>  
>  	cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
>  	if (!cpudata)
> @@ -959,8 +958,8 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	cpudata->cpu = policy->cpu;
>  	cpudata->epp_policy = 0;
>  
> -	rc = amd_pstate_init_perf(cpudata);
> -	if (rc)
> +	ret = amd_pstate_init_perf(cpudata);
> +	if (ret)
>  		goto free_cpudata1;
>  
>  	min_freq = amd_get_min_freq(cpudata);
> @@ -1076,9 +1075,9 @@ static void amd_pstate_epp_init(unsigned int cpu)
>  		value |= (u64)epp << 24;
>  	}
>  
> +	amd_pstate_set_epp(cpudata, epp);
>  skip_epp:
>  	WRITE_ONCE(cpudata->cppc_req_cached, value);
> -	amd_pstate_set_epp(cpudata, epp);
>  	cpufreq_cpu_put(policy);
>  }
> 

Tested this on AMD Milan (Zen 3) system.

Tested-by: Wyes Karny <wyes.karny@amd.com>

> -- 
> 2.39.1
>
  

[AMD Official Use Only - General]

Hi Arnd,

> -----Original Message-----
> From: Arnd Bergmann <arnd@kernel.org>
> Sent: Wednesday, February 8, 2023 12:13 AM
> To: Huang, Ray <Ray.Huang@amd.com>; Rafael J. Wysocki
> <rafael@kernel.org>; Viresh Kumar <viresh.kumar@linaro.org>; Karny, Wyes
> <Wyes.Karny@amd.com>; Yuan, Perry <Perry.Yuan@amd.com>; Limonciello,
> Mario <Mario.Limonciello@amd.com>
> Cc: Arnd Bergmann <arnd@arndb.de>; Yuan, Perry <Perry.Yuan@amd.com>;
> Limonciello, Mario <Mario.Limonciello@amd.com>; Jinzhou Su
> <Jinzhou.Su@amd.com>; Meng, Li (Jassmine) <Li.Meng@amd.com>; linux-
> pm@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: [PATCH] cpufreq: amd-pstate: avoid uninitialized variable use
> 
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The new epp support causes warnings about three separate but related bugs:
> 
> 1) failing before allocation should just return an error:
> 
> drivers/cpufreq/amd-pstate.c:951:6: error: variable 'ret' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (!dev)
>             ^~~~
> drivers/cpufreq/amd-pstate.c:1018:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> 
> 2) wrong variable to store return code:
> 
> drivers/cpufreq/amd-pstate.c:963:6: error: variable 'ret' is used uninitialized
> whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (rc)
>             ^~
> drivers/cpufreq/amd-pstate.c:1019:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> drivers/cpufreq/amd-pstate.c:963:2: note: remove the 'if' if its condition is
> always false
>         if (rc)
>         ^~~~~~~
> 
> 3) calling amd_pstate_set_epp() in cleanup path after determining that it
> should not be called:
> 
> drivers/cpufreq/amd-pstate.c:1055:6: error: variable 'epp' is used
> uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-
> uninitialized]
>         if (cpudata->epp_policy == cpudata->policy)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/cpufreq/amd-pstate.c:1080:30: note: uninitialized use occurs here
>         amd_pstate_set_epp(cpudata, epp);
>                                     ^~~
> 
> All three are trivial to fix, but most likely there are additional bugs in this
> function when the error handling was not really tested.
> 
> Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support
> for the AMD processors")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/cpufreq/amd-pstate.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 168a28bed6ee..847f5f31396d 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -940,7 +940,6 @@ static int amd_pstate_epp_cpu_init(struct
> cpufreq_policy *policy)
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
>  	struct amd_cpudata *cpudata;
>  	struct device *dev;
> -	int rc;
>  	u64 value;
> 
>  	/*
> @@ -950,7 +949,7 @@ static int amd_pstate_epp_cpu_init(struct
> cpufreq_policy *policy)
>  	amd_perf_ctl_reset(policy->cpu);
>  	dev = get_cpu_device(policy->cpu);
>  	if (!dev)
> -		goto free_cpudata1;
> +		return -ENODEV;
> 
>  	cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
>  	if (!cpudata)
> @@ -959,8 +958,8 @@ static int amd_pstate_epp_cpu_init(struct
> cpufreq_policy *policy)
>  	cpudata->cpu = policy->cpu;
>  	cpudata->epp_policy = 0;
> 
> -	rc = amd_pstate_init_perf(cpudata);
> -	if (rc)
> +	ret = amd_pstate_init_perf(cpudata);
> +	if (ret)
>  		goto free_cpudata1;
> 
>  	min_freq = amd_get_min_freq(cpudata);
> @@ -1076,9 +1075,9 @@ static void amd_pstate_epp_init(unsigned int cpu)
>  		value |= (u64)epp << 24;
>  	}
> 
> +	amd_pstate_set_epp(cpudata, epp);
>  skip_epp:
>  	WRITE_ONCE(cpudata->cppc_req_cached, value);
> -	amd_pstate_set_epp(cpudata, epp);
>  	cpufreq_cpu_put(policy);
>  }
> 
> --
> 2.39.1

Thanks for your quick fix patch.
 
Reviewed-by: Yuan Perry <Perry.Yuan@amd.com>
  

On Wed, Feb 08, 2023 at 12:12:51AM +0800, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The new epp support causes warnings about three separate
> but related bugs:
> 
> 1) failing before allocation should just return an error:
> 
> drivers/cpufreq/amd-pstate.c:951:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (!dev)
>             ^~~~
> drivers/cpufreq/amd-pstate.c:1018:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> 
> 2) wrong variable to store return code:
> 
> drivers/cpufreq/amd-pstate.c:963:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (rc)
>             ^~
> drivers/cpufreq/amd-pstate.c:1019:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> drivers/cpufreq/amd-pstate.c:963:2: note: remove the 'if' if its condition is always false
>         if (rc)
>         ^~~~~~~
> 
> 3) calling amd_pstate_set_epp() in cleanup path after determining
> that it should not be called:
> 
> drivers/cpufreq/amd-pstate.c:1055:6: error: variable 'epp' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (cpudata->epp_policy == cpudata->policy)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/cpufreq/amd-pstate.c:1080:30: note: uninitialized use occurs here
>         amd_pstate_set_epp(cpudata, epp);
>                                     ^~~
> 
> All three are trivial to fix, but most likely there are additional bugs
> in this function when the error handling was not really tested.
> 
> Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks!

Acked-by: Huang Rui <ray.huang@amd.com>

> ---
>  drivers/cpufreq/amd-pstate.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 168a28bed6ee..847f5f31396d 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -940,7 +940,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
>  	struct amd_cpudata *cpudata;
>  	struct device *dev;
> -	int rc;
>  	u64 value;
>  
>  	/*
> @@ -950,7 +949,7 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	amd_perf_ctl_reset(policy->cpu);
>  	dev = get_cpu_device(policy->cpu);
>  	if (!dev)
> -		goto free_cpudata1;
> +		return -ENODEV;
>  
>  	cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
>  	if (!cpudata)
> @@ -959,8 +958,8 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  	cpudata->cpu = policy->cpu;
>  	cpudata->epp_policy = 0;
>  
> -	rc = amd_pstate_init_perf(cpudata);
> -	if (rc)
> +	ret = amd_pstate_init_perf(cpudata);
> +	if (ret)
>  		goto free_cpudata1;
>  
>  	min_freq = amd_get_min_freq(cpudata);
> @@ -1076,9 +1075,9 @@ static void amd_pstate_epp_init(unsigned int cpu)
>  		value |= (u64)epp << 24;
>  	}
>  
> +	amd_pstate_set_epp(cpudata, epp);
>  skip_epp:
>  	WRITE_ONCE(cpudata->cppc_req_cached, value);
> -	amd_pstate_set_epp(cpudata, epp);
>  	cpufreq_cpu_put(policy);
>  }
>  
> -- 
> 2.39.1
>
  

Hi Arnd, Ray, Perry,

On 07 Feb 17:12, Arnd Bergmann wrote:
> @@ -1076,9 +1075,9 @@ static void amd_pstate_epp_init(unsigned int cpu)
>  		value |= (u64)epp << 24;
>  	}
>  
> +	amd_pstate_set_epp(cpudata, epp);
>  skip_epp:
>  	WRITE_ONCE(cpudata->cppc_req_cached, value);
> -	amd_pstate_set_epp(cpudata, epp);
>  	cpufreq_cpu_put(policy);
>  }

I see an issue here with MSR-based systems.
Here EPP is being set before updating `cppc_req_cached` and for MSR
based systems while updating EPP value, MIN_PERF and MAX_PERF also
updated. So, here whatever value MSR_AMD_CPPC_REQ had for min and max
perf that will be rewritten instead of highest and lowest perf from
MSR_AMD_CPPC_CAP1.

Can we do something like this:

@@ -1053,32 +1052,34 @@ static void amd_pstate_epp_init(unsigned int
cpu)
        value &= ~AMD_CPPC_DES_PERF(~0L);
        value |= AMD_CPPC_DES_PERF(0);

+       /* No need to set epp again if previous and current policy is same */
        if (cpudata->epp_policy == cpudata->policy)
                goto skip_epp;

        cpudata->epp_policy = cpudata->policy;

-       if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE) {
-               epp = amd_pstate_get_epp(cpudata, value);
-               if (epp < 0)
-                       goto skip_epp;
-               /* force the epp value to be zero for performance policy */
-               epp = 0;
-       } else {
-               /* Get BIOS pre-defined epp value */
-               epp = amd_pstate_get_epp(cpudata, value);
-               if (epp)
-                       goto skip_epp;
+       /* Get BIOS pre-defined epp value */
+       epp = amd_pstate_get_epp(cpudata, value);
+       if (epp < 0) {
+               /**
+                * This return value can only be negative for shared_memory
+                * systems where EPP register read/write not supported.
+                */
+               goto skip_epp;
        }
+
+       if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
+               epp = 0;
+
        /* Set initial EPP value */
        if (boot_cpu_has(X86_FEATURE_CPPC)) {
                value &= ~GENMASK_ULL(31, 24);
                value |= (u64)epp << 24;
        }

-skip_epp:
        WRITE_ONCE(cpudata->cppc_req_cached, value);
        amd_pstate_set_epp(cpudata, epp);
+skip_epp:
        cpufreq_cpu_put(policy);
 }


>  
> -- 
> 2.39.1
>
  

On Thu, Feb 9, 2023 at 6:04 AM Huang Rui <ray.huang@amd.com> wrote:
>
> On Wed, Feb 08, 2023 at 12:12:51AM +0800, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > The new epp support causes warnings about three separate
> > but related bugs:
> >
> > 1) failing before allocation should just return an error:
> >
> > drivers/cpufreq/amd-pstate.c:951:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
> >         if (!dev)
> >             ^~~~
> > drivers/cpufreq/amd-pstate.c:1018:9: note: uninitialized use occurs here
> >         return ret;
> >                ^~~
> >
> > 2) wrong variable to store return code:
> >
> > drivers/cpufreq/amd-pstate.c:963:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
> >         if (rc)
> >             ^~
> > drivers/cpufreq/amd-pstate.c:1019:9: note: uninitialized use occurs here
> >         return ret;
> >                ^~~
> > drivers/cpufreq/amd-pstate.c:963:2: note: remove the 'if' if its condition is always false
> >         if (rc)
> >         ^~~~~~~
> >
> > 3) calling amd_pstate_set_epp() in cleanup path after determining
> > that it should not be called:
> >
> > drivers/cpufreq/amd-pstate.c:1055:6: error: variable 'epp' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
> >         if (cpudata->epp_policy == cpudata->policy)
> >             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/cpufreq/amd-pstate.c:1080:30: note: uninitialized use occurs here
> >         amd_pstate_set_epp(cpudata, epp);
> >                                     ^~~
> >
> > All three are trivial to fix, but most likely there are additional bugs
> > in this function when the error handling was not really tested.
> >
> > Fixes: ffa5096a7c33 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Thanks!
>
> Acked-by: Huang Rui <ray.huang@amd.com>
>
> > ---
> >  drivers/cpufreq/amd-pstate.c | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> > index 168a28bed6ee..847f5f31396d 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -940,7 +940,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> >       int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
> >       struct amd_cpudata *cpudata;
> >       struct device *dev;
> > -     int rc;
> >       u64 value;
> >
> >       /*
> > @@ -950,7 +949,7 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> >       amd_perf_ctl_reset(policy->cpu);
> >       dev = get_cpu_device(policy->cpu);
> >       if (!dev)
> > -             goto free_cpudata1;
> > +             return -ENODEV;
> >
> >       cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
> >       if (!cpudata)
> > @@ -959,8 +958,8 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> >       cpudata->cpu = policy->cpu;
> >       cpudata->epp_policy = 0;
> >
> > -     rc = amd_pstate_init_perf(cpudata);
> > -     if (rc)
> > +     ret = amd_pstate_init_perf(cpudata);
> > +     if (ret)
> >               goto free_cpudata1;
> >
> >       min_freq = amd_get_min_freq(cpudata);
> > @@ -1076,9 +1075,9 @@ static void amd_pstate_epp_init(unsigned int cpu)
> >               value |= (u64)epp << 24;
> >       }
> >
> > +     amd_pstate_set_epp(cpudata, epp);
> >  skip_epp:
> >       WRITE_ONCE(cpudata->cppc_req_cached, value);
> > -     amd_pstate_set_epp(cpudata, epp);
> >       cpufreq_cpu_put(policy);
> >  }
> >
> > --

Applied, thanks!