MSR fixes and cleanups after last round of MSR cleanups

[PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Xin Li (Intel) 7 months, 1 week ago

xen_read_msr_safe() currently passes an uninitialized argument err to
xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
xen_read_msr_safe() could return err with an unpredictable value.

To ensure correctness, initialize err to 0 (representing success)
in xen_read_msr_safe().

Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(),
the latter should be responsible for initializing the value of *err to 0.
Thus initialize *err to 0 in xen_do_read_msr().

Fixes: 502ad6e5a619 ("x86/msr: Change the function type of native_read_msr_safe()")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
---
 arch/x86/xen/enlighten_pv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 3be38350f044..01f1d441347e 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
 {
 	u64 val = 0;	/* Avoid uninitialized value for safe variant. */
 
+	if (err)
+		*err = 0;
+
 	if (pmu_msr_chk_emulated(msr, &val, true))
 		return val;
 
@@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
 
 static int xen_read_msr_safe(u32 msr, u64 *val)
 {
-	int err;
+	int err = 0;
 
 	*val = xen_do_read_msr(msr, &err);
 	return err;
-- 
2.49.0

Re: [PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Ingo Molnar 7 months ago

* Xin Li (Intel) <xin@zytor.com> wrote:

> xen_read_msr_safe() currently passes an uninitialized argument err to
> xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
> xen_read_msr_safe() could return err with an unpredictable value.
> 
> To ensure correctness, initialize err to 0 (representing success)
> in xen_read_msr_safe().
> 
> Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(),
> the latter should be responsible for initializing the value of *err to 0.
> Thus initialize *err to 0 in xen_do_read_msr().
> 
> Fixes: 502ad6e5a619 ("x86/msr: Change the function type of native_read_msr_safe()")
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> ---
>  arch/x86/xen/enlighten_pv.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 3be38350f044..01f1d441347e 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
>  {
>  	u64 val = 0;	/* Avoid uninitialized value for safe variant. */
>  
> +	if (err)
> +		*err = 0;
> +
>  	if (pmu_msr_chk_emulated(msr, &val, true))
>  		return val;
>  
> @@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
>  
>  static int xen_read_msr_safe(u32 msr, u64 *val)
>  {
> -	int err;
> +	int err = 0;
>  
>  	*val = xen_do_read_msr(msr, &err);
>  	return err;

So why not initialize 'err' with 0 in both callers, xen_read_msr_safe() 
and xen_read_msr(), and avoid all the initialization trouble in 
xen_do_read_msr()?

Thanks,

	Ingo

Re: [PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Xin Li 7 months ago

On 5/15/2025 8:29 AM, Ingo Molnar wrote:
> 
> * Xin Li (Intel) <xin@zytor.com> wrote:
> 
>> xen_read_msr_safe() currently passes an uninitialized argument err to
>> xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
>> xen_read_msr_safe() could return err with an unpredictable value.
>>
>> To ensure correctness, initialize err to 0 (representing success)
>> in xen_read_msr_safe().
>>
>> Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(),
>> the latter should be responsible for initializing the value of *err to 0.
>> Thus initialize *err to 0 in xen_do_read_msr().
>>
>> Fixes: 502ad6e5a619 ("x86/msr: Change the function type of native_read_msr_safe()")
>> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
>> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
>> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
>> ---
>>   arch/x86/xen/enlighten_pv.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>> index 3be38350f044..01f1d441347e 100644
>> --- a/arch/x86/xen/enlighten_pv.c
>> +++ b/arch/x86/xen/enlighten_pv.c
>> @@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
>>   {
>>   	u64 val = 0;	/* Avoid uninitialized value for safe variant. */
>>   
>> +	if (err)
>> +		*err = 0;
>> +
>>   	if (pmu_msr_chk_emulated(msr, &val, true))
>>   		return val;
>>   
>> @@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
>>   
>>   static int xen_read_msr_safe(u32 msr, u64 *val)
>>   {
>> -	int err;
>> +	int err = 0;
>>   
>>   	*val = xen_do_read_msr(msr, &err);
>>   	return err;
> 
> So why not initialize 'err' with 0 in both callers, xen_read_msr_safe()
> and xen_read_msr(), and avoid all the initialization trouble in
> xen_do_read_msr()?

Yeah, I should make the change in xen_read_msr() too.

However xen_do_read_msr() should be implemented in a defensive way to
set *err properly as it's part of its return value.  Actually it was so,
but one of my previous cleanup patch removed it because err is no longer
passed to pmu_msr_chk_emulated().

Thanks!
     Xin

Re: [PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Jürgen Groß 7 months ago

On 15.05.25 20:11, Xin Li wrote:
> On 5/15/2025 8:29 AM, Ingo Molnar wrote:
>>
>> * Xin Li (Intel) <xin@zytor.com> wrote:
>>
>>> xen_read_msr_safe() currently passes an uninitialized argument err to
>>> xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
>>> xen_read_msr_safe() could return err with an unpredictable value.
>>>
>>> To ensure correctness, initialize err to 0 (representing success)
>>> in xen_read_msr_safe().
>>>
>>> Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(),
>>> the latter should be responsible for initializing the value of *err to 0.
>>> Thus initialize *err to 0 in xen_do_read_msr().
>>>
>>> Fixes: 502ad6e5a619 ("x86/msr: Change the function type of 
>>> native_read_msr_safe()")
>>> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
>>> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
>>> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
>>> ---
>>>   arch/x86/xen/enlighten_pv.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>>> index 3be38350f044..01f1d441347e 100644
>>> --- a/arch/x86/xen/enlighten_pv.c
>>> +++ b/arch/x86/xen/enlighten_pv.c
>>> @@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
>>>   {
>>>       u64 val = 0;    /* Avoid uninitialized value for safe variant. */
>>> +    if (err)
>>> +        *err = 0;
>>> +
>>>       if (pmu_msr_chk_emulated(msr, &val, true))
>>>           return val;
>>> @@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
>>>   static int xen_read_msr_safe(u32 msr, u64 *val)
>>>   {
>>> -    int err;
>>> +    int err = 0;
>>>       *val = xen_do_read_msr(msr, &err);
>>>       return err;
>>
>> So why not initialize 'err' with 0 in both callers, xen_read_msr_safe()
>> and xen_read_msr(), and avoid all the initialization trouble in
>> xen_do_read_msr()?
> 
> Yeah, I should make the change in xen_read_msr() too.
> 
> However xen_do_read_msr() should be implemented in a defensive way to
> set *err properly as it's part of its return value.  Actually it was so,
> but one of my previous cleanup patch removed it because err is no longer
> passed to pmu_msr_chk_emulated().

xen_do_read_msr() is usable only in enlighten_pv.c as it is static.

So I'd prefer to drop setting err to 0 in xen_do_read_msr() initially
and to set err to 0 in all callers.


Juergen

Re: [PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Xin Li 7 months ago

On 5/16/2025 6:42 AM, Jürgen Groß wrote:
> On 15.05.25 20:11, Xin Li wrote:
>> On 5/15/2025 8:29 AM, Ingo Molnar wrote:
>>>
>>> * Xin Li (Intel) <xin@zytor.com> wrote:
>>>
>>>> xen_read_msr_safe() currently passes an uninitialized argument err to
>>>> xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
>>>> xen_read_msr_safe() could return err with an unpredictable value.
>>>>
>>>> To ensure correctness, initialize err to 0 (representing success)
>>>> in xen_read_msr_safe().
>>>>
>>>> Because xen_read_msr_safe() is essentially a wrapper of 
>>>> xen_do_read_msr(),
>>>> the latter should be responsible for initializing the value of *err 
>>>> to 0.
>>>> Thus initialize *err to 0 in xen_do_read_msr().
>>>>
>>>> Fixes: 502ad6e5a619 ("x86/msr: Change the function type of 
>>>> native_read_msr_safe()")
>>>> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
>>>> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0- 
>>>> MhtBSZG@stanley.mountain/
>>>> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
>>>> ---
>>>>   arch/x86/xen/enlighten_pv.c | 5 ++++-
>>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>>>> index 3be38350f044..01f1d441347e 100644
>>>> --- a/arch/x86/xen/enlighten_pv.c
>>>> +++ b/arch/x86/xen/enlighten_pv.c
>>>> @@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
>>>>   {
>>>>       u64 val = 0;    /* Avoid uninitialized value for safe variant. */
>>>> +    if (err)
>>>> +        *err = 0;
>>>> +
>>>>       if (pmu_msr_chk_emulated(msr, &val, true))
>>>>           return val;
>>>> @@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, 
>>>> int *err)
>>>>   static int xen_read_msr_safe(u32 msr, u64 *val)
>>>>   {
>>>> -    int err;
>>>> +    int err = 0;
>>>>       *val = xen_do_read_msr(msr, &err);
>>>>       return err;
>>>
>>> So why not initialize 'err' with 0 in both callers, xen_read_msr_safe()
>>> and xen_read_msr(), and avoid all the initialization trouble in
>>> xen_do_read_msr()?
>>
>> Yeah, I should make the change in xen_read_msr() too.
>>
>> However xen_do_read_msr() should be implemented in a defensive way to
>> set *err properly as it's part of its return value.  Actually it was so,
>> but one of my previous cleanup patch removed it because err is no longer
>> passed to pmu_msr_chk_emulated().
> 
> xen_do_read_msr() is usable only in enlighten_pv.c as it is static.
> 
> So I'd prefer to drop setting err to 0 in xen_do_read_msr() initially
> and to set err to 0 in all callers.

Okay, I will send v1A to address this comment then.

Thanks!
     Xin

> Juergen

[PATCH v1A 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Xin Li (Intel) 7 months ago

xen_read_msr_safe() currently passes an uninitialized argument err to
xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
xen_read_msr_safe() could return err with an unpredictable value.

To ensure correctness, initialize err to 0 (representing success)
in xen_read_msr_safe().

Do the same in xen_read_msr(), even err is not used after being passed
to xen_do_read_msr().

Fixes: d815da84fdd0 ("x86/msr: Change the function type of native_read_msr_safe()"
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
---

Change in v1A:
*) Drop setting err to 0 in xen_do_read_msr() initially and set err to
   0 in all callers (Jürgen Groß).
---
 arch/x86/xen/enlighten_pv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 7f9ded1bc707..26bbaf4b7330 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1162,7 +1162,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
 
 static int xen_read_msr_safe(u32 msr, u64 *val)
 {
-	int err;
+	int err = 0;
 
 	*val = xen_do_read_msr(msr, &err);
 	return err;
@@ -1179,7 +1179,7 @@ static int xen_write_msr_safe(u32 msr, u64 val)
 
 static u64 xen_read_msr(u32 msr)
 {
-	int err;
+	int err = 0;
 
 	return xen_do_read_msr(msr, xen_msr_safe ? &err : NULL);
 }
-- 
2.49.0

Re: [PATCH v1A 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Jürgen Groß 7 months ago

On 17.05.25 18:57, Xin Li (Intel) wrote:
> xen_read_msr_safe() currently passes an uninitialized argument err to
> xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
> xen_read_msr_safe() could return err with an unpredictable value.
> 
> To ensure correctness, initialize err to 0 (representing success)
> in xen_read_msr_safe().
> 
> Do the same in xen_read_msr(), even err is not used after being passed
> to xen_do_read_msr().
> 
> Fixes: d815da84fdd0 ("x86/msr: Change the function type of native_read_msr_safe()"
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

[tip: x86/core] x86/xen/msr: Fix uninitialized variable 'err'

Posted by tip-bot2 for Xin Li (Intel) 7 months ago

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     e95534e107d2e9e136aa4d7cbededb3827e80074
Gitweb:        https://git.kernel.org/tip/e95534e107d2e9e136aa4d7cbededb3827e80074
Author:        Xin Li (Intel) <xin@zytor.com>
AuthorDate:    Sat, 17 May 2025 09:57:12 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 21 May 2025 08:44:31 +02:00

x86/xen/msr: Fix uninitialized variable 'err'

xen_read_msr_safe() currently passes an uninitialized argument 'err' to
xen_do_read_msr(). But as xen_do_read_msr() may not set the argument,
xen_read_msr_safe() could return err with an unpredictable value.

To ensure correctness, initialize err to 0 (representing success)
in xen_read_msr_safe().

Do the same in xen_read_msr(), even err is not used after being passed
to xen_do_read_msr().

Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Link: https://lore.kernel.org/r/20250517165713.935384-1-xin@zytor.com
---
 arch/x86/xen/enlighten_pv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 7f9ded1..26bbaf4 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1162,7 +1162,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
 
 static int xen_read_msr_safe(u32 msr, u64 *val)
 {
-	int err;
+	int err = 0;
 
 	*val = xen_do_read_msr(msr, &err);
 	return err;
@@ -1179,7 +1179,7 @@ static int xen_write_msr_safe(u32 msr, u64 val)
 
 static u64 xen_read_msr(u32 msr)
 {
-	int err;
+	int err = 0;
 
 	return xen_do_read_msr(msr, xen_msr_safe ? &err : NULL);
 }

[tip: x86/core] x86/xen/msr: Fix uninitialized variable 'err'

Posted by tip-bot2 for Xin Li (Intel) 7 months ago

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     54c2c688cd9305bdbab4883b9da6ff63f4deca5d
Gitweb:        https://git.kernel.org/tip/54c2c688cd9305bdbab4883b9da6ff63f4deca5d
Author:        Xin Li (Intel) <xin@zytor.com>
AuthorDate:    Sat, 17 May 2025 09:57:12 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 18 May 2025 08:39:16 +02:00

x86/xen/msr: Fix uninitialized variable 'err'

xen_read_msr_safe() currently passes an uninitialized argument 'err' to
xen_do_read_msr(). But as xen_do_read_msr() may not set the argument,
xen_read_msr_safe() could return err with an unpredictable value.

To ensure correctness, initialize err to 0 (representing success)
in xen_read_msr_safe().

Do the same in xen_read_msr(), even err is not used after being passed
to xen_do_read_msr().

Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
Fixes: d815da84fdd0 ("x86/msr: Change the function type of native_read_msr_safe()"
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Link: https://lore.kernel.org/r/20250517165713.935384-1-xin@zytor.com
---
 arch/x86/xen/enlighten_pv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 7f9ded1..26bbaf4 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1162,7 +1162,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
 
 static int xen_read_msr_safe(u32 msr, u64 *val)
 {
-	int err;
+	int err = 0;
 
 	*val = xen_do_read_msr(msr, &err);
 	return err;
@@ -1179,7 +1179,7 @@ static int xen_write_msr_safe(u32 msr, u64 val)
 
 static u64 xen_read_msr(u32 msr)
 {
-	int err;
+	int err = 0;
 
 	return xen_do_read_msr(msr, xen_msr_safe ? &err : NULL);
 }

Re: [PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

Posted by Ingo Molnar 7 months ago

* Xin Li <xin@zytor.com> wrote:

> On 5/15/2025 8:29 AM, Ingo Molnar wrote:
> > 
> > * Xin Li (Intel) <xin@zytor.com> wrote:
> > 
> > > xen_read_msr_safe() currently passes an uninitialized argument err to
> > > xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
> > > xen_read_msr_safe() could return err with an unpredictable value.
> > > 
> > > To ensure correctness, initialize err to 0 (representing success)
> > > in xen_read_msr_safe().
> > > 
> > > Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(),
> > > the latter should be responsible for initializing the value of *err to 0.
> > > Thus initialize *err to 0 in xen_do_read_msr().
> > > 
> > > Fixes: 502ad6e5a619 ("x86/msr: Change the function type of native_read_msr_safe()")
> > > Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> > > Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
> > > Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> > > ---
> > >   arch/x86/xen/enlighten_pv.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> > > index 3be38350f044..01f1d441347e 100644
> > > --- a/arch/x86/xen/enlighten_pv.c
> > > +++ b/arch/x86/xen/enlighten_pv.c
> > > @@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
> > >   {
> > >   	u64 val = 0;	/* Avoid uninitialized value for safe variant. */
> > > +	if (err)
> > > +		*err = 0;
> > > +
> > >   	if (pmu_msr_chk_emulated(msr, &val, true))
> > >   		return val;
> > > @@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
> > >   static int xen_read_msr_safe(u32 msr, u64 *val)
> > >   {
> > > -	int err;
> > > +	int err = 0;
> > >   	*val = xen_do_read_msr(msr, &err);
> > >   	return err;
> > 
> > So why not initialize 'err' with 0 in both callers, xen_read_msr_safe()
> > and xen_read_msr(), and avoid all the initialization trouble in
> > xen_do_read_msr()?
> 
> Yeah, I should make the change in xen_read_msr() too.
> 
> However xen_do_read_msr() should be implemented in a defensive way to
> set *err properly as it's part of its return value.  Actually it was so,
> but one of my previous cleanup patch removed it because err is no longer
> passed to pmu_msr_chk_emulated().

Maybe. It's up to Juergen though.

Thanks,

	Ingo