[PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[Peng Hao]

From: Peng Hao <peng.hao2@zte.com.cn>

  modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
---
 arch/x86/kvm/svm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d96092b..bf1ded4 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -262,7 +262,7 @@ struct amd_svm_iommu_ir {
 };
 
 #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK	(0xFF)
-#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK		(1 << 31)
+#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK		(1UL << 31)
 
 #define AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK	(0xFFULL)
 #define AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK	(0xFFFFFFFFFFULL << 12)
-- 
1.8.3.1

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[Wei Yang]

On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>
>From: Peng Hao <peng.hao2@zte.com.cn>
>
>  modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>
>Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
>---
> arch/x86/kvm/svm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>index d96092b..bf1ded4 100644
>--- a/arch/x86/kvm/svm.c
>+++ b/arch/x86/kvm/svm.c
>@@ -262,7 +262,7 @@ struct amd_svm_iommu_ir {
> };
> 
> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK	(0xFF)
>-#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK		(1 << 31)
>+#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK		(1UL << 31)

It is reasonable to change to unsigned, while not necessary to unsigned
long?

> 
> #define AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK	(0xFFULL)
> #define AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK	(0xFFFFFFFFFFULL << 12)
>-- 
>1.8.3.1
>

-- 
Wei Yang
Help you, Help me

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[Wei Yang]

On Sat, Oct 06, 2018 at 11:31:04AM +0800, peng.hao2@zte.com.cn wrote:
>>On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>>>
>>>From: Peng Hao <peng.hao2@zte.com.cn>
>>>
>>>  modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>>>
>>>Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
>>>---
>>> arch/x86/kvm/svm.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>>diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>>index d96092b..bf1ded4 100644
>>>--- a/arch/x86/kvm/svm.c
>>>+++ b/arch/x86/kvm/svm.c
>>>@@ -262,7 +262,7 @@ struct amd_svm_iommu_ir {
>>> };
>>>
>>> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK    (0xFF)
>>>-#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1 << 31)
>>>+#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1UL << 31)
>
>>It is reasonable to change to unsigned, while not necessary to unsigned
>>long?
>AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used in function avic_ldr_write.
>here I think it doesn't matter if you use unsigned or unsigned long. Do you have any suggestions?

In current case, AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used to calculate
the value of new_entry with type of u32. So the definition here is not
harmful.

Also, I did a quick grep and found similar definition (1 << 31) is popular
in the whole kernel tree.

The reason to make this change is not that strong to me. Would you
minding sharing more reason behind this change?

>>--
>>Wei Yang
>>Help you, Help me


-- 
Wei Yang
Help you, Help me

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[Wei Yang]

On Mon, Oct 08, 2018 at 09:04:34AM +0800, peng.hao2@zte.com.cn wrote:
>>On Sat, Oct 06, 2018 at 11:31:04AM +0800, peng.hao2@zte.com.cn wrote:
>>>>On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>>>>>
>>>>>From: Peng Hao <peng.hao2@zte.com.cn>
>>>>>
>>>>>  modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>>>>>
>>>>>Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
>>>>>---
>>>>> arch/x86/kvm/svm.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>>diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>>>>index d96092b..bf1ded4 100644
>>>>>--- a/arch/x86/kvm/svm.c
>>>>>+++ b/arch/x86/kvm/svm.c
>>>>>@@ -262,7 +262,7 @@ struct amd_svm_iommu_ir {
>>>>> };
>>>>>
>>>>> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK    (0xFF)
>>>>>-#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1 << 31)
>>>>>+#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1UL << 31)
>>>
>>>>It is reasonable to change to unsigned, while not necessary to unsigned
>>>>long?
>>>AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used in function avic_ldr_write.
>>>here I think it doesn't matter if you use unsigned or unsigned long. Do you have any suggestions?
>
>>In current case, AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used to calculate
>>the value of new_entry with type of u32. So the definition here is not
>>harmful.
>
>>Also, I did a quick grep and found similar definition (1 << 31) is popular
>>in the whole kernel tree.
>
>>The reason to make this change is not that strong to me. Would you
>>minding sharing more reason behind this change?
>oh, I'm just thinking logically, not more reason.

This definition may introduce problem when this value is used to
calculate a 64bit data.

Since current entry is 32bit, we may leave it as it is for now.


-- 
Wei Yang
Help you, Help me

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[Paolo Bonzini]

On 08/10/2018 04:25, Wei Yang wrote:
> On Mon, Oct 08, 2018 at 09:04:34AM +0800, peng.hao2@zte.com.cn wrote:
>>> On Sat, Oct 06, 2018 at 11:31:04AM +0800, peng.hao2@zte.com.cn wrote:
>>>>> On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>>>>>>
>>>>>> From: Peng Hao <peng.hao2@zte.com.cn>
>>>>>>
>>>>>>  modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>>>>>>
>>>>>> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
>>>>>> ---
>>>>>> arch/x86/kvm/svm.c | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>>>>> index d96092b..bf1ded4 100644
>>>>>> --- a/arch/x86/kvm/svm.c
>>>>>> +++ b/arch/x86/kvm/svm.c
>>>>>> @@ -262,7 +262,7 @@ struct amd_svm_iommu_ir {
>>>>>> };
>>>>>>
>>>>>> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK    (0xFF)
>>>>>> -#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1 << 31)
>>>>>> +#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1UL << 31)
>>>>
>>>>> It is reasonable to change to unsigned, while not necessary to unsigned
>>>>> long?
>>>> AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used in function avic_ldr_write.
>>>> here I think it doesn't matter if you use unsigned or unsigned long. Do you have any suggestions?
>>
>>> In current case, AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used to calculate
>>> the value of new_entry with type of u32. So the definition here is not
>>> harmful.
>>
>>> Also, I did a quick grep and found similar definition (1 << 31) is popular
>>> in the whole kernel tree.
>>
>>> The reason to make this change is not that strong to me. Would you
>>> minding sharing more reason behind this change?
>> oh, I'm just thinking logically, not more reason.
> 
> This definition may introduce problem when this value is used to
> calculate a 64bit data.
> 
> Since current entry is 32bit, we may leave it as it is for now.

I agree.

Paolo

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[H. Peter Anvin]

On 10/7/18 6:04 PM, peng.hao2@zte.com.cn wrote:
\>>>>>
>>>>> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK    (0xFF)
>>>>> -#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1 << 31)
>>>>> +#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1UL << 31)
>>>
>>>> It is reasonable to change to unsigned, while not necessary to unsigned
>>>> long?
>>> AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used in function avic_ldr_write.
>>> here I think it doesn't matter if you use unsigned or unsigned long. Do you have any suggestions?
> 
>> In current case, AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used to calculate
>> the value of new_entry with type of u32. So the definition here is not
>> harmful.
> 
>> Also, I did a quick grep and found similar definition (1 << 31) is popular
>> in the whole kernel tree.
> 
>> The reason to make this change is not that strong to me. Would you
>> minding sharing more reason behind this change?
> oh, I'm just thinking logically, not more reason.

The right way to do this would be to use the _BITUL() (or _BITULL()) macro.

	-hpa

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[Paolo Bonzini]

On 15/10/2018 19:16, H. Peter Anvin wrote:
> On 10/7/18 6:04 PM, peng.hao2@zte.com.cn wrote:
> \>>>>>
>>>>>> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK    (0xFF)
>>>>>> -#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1 << 31)
>>>>>> +#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK        (1UL << 31)
>>>>
>>>>> It is reasonable to change to unsigned, while not necessary to unsigned
>>>>> long?
>>>> AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used in function avic_ldr_write.
>>>> here I think it doesn't matter if you use unsigned or unsigned long. Do you have any suggestions?
>>
>>> In current case, AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used to calculate
>>> the value of new_entry with type of u32. So the definition here is not
>>> harmful.
>>
>>> Also, I did a quick grep and found similar definition (1 << 31) is popular
>>> in the whole kernel tree.
>>
>>> The reason to make this change is not that strong to me. Would you
>>> minding sharing more reason behind this change?
>> oh, I'm just thinking logically, not more reason.
> 
> The right way to do this would be to use the _BITUL() (or _BITULL()) macro.

Even for a value from a 32-bit register?  That would be _BIT, which
doesn't exist.

Paolo

Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits

[H. Peter Anvin]

On 10/15/18 10:23 AM, Paolo Bonzini wrote:
> 
> Even for a value from a 32-bit register?  That would be _BIT, which
> doesn't exist.
> 

Just use _BITUL(). gcc is smart enough to know that that the resulting value
is representable in 32 bits.

Or if you really care, submit a patch to create _BITU(), but I don't
personally see much of a point.

	-hpa