2018-10-04 17:48:10

by Peng Hao

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

From: Peng Hao <[email protected]>

modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned

Signed-off-by: Peng Hao <[email protected]>
---
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

2018-10-06 02:13:14

by Wei Yang

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

On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>
>From: Peng Hao <[email protected]>
>
> modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>
>Signed-off-by: Peng Hao <[email protected]>
>---
> 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

2018-10-06 07:09:12

by Wei Yang

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

On Sat, Oct 06, 2018 at 11:31:04AM +0800, [email protected] wrote:
>>On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>>>
>>>From: Peng Hao <[email protected]>
>>>
>>> modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>>>
>>>Signed-off-by: Peng Hao <[email protected]>
>>>---
>>> 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

2018-10-08 02:25:56

by Wei Yang

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

On Mon, Oct 08, 2018 at 09:04:34AM +0800, [email protected] wrote:
>>On Sat, Oct 06, 2018 at 11:31:04AM +0800, [email protected] wrote:
>>>>On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>>>>>
>>>>>From: Peng Hao <[email protected]>
>>>>>
>>>>> modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>>>>>
>>>>>Signed-off-by: Peng Hao <[email protected]>
>>>>>---
>>>>> 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

2018-10-15 17:14:42

by Paolo Bonzini

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

On 08/10/2018 04:25, Wei Yang wrote:
> On Mon, Oct 08, 2018 at 09:04:34AM +0800, [email protected] wrote:
>>> On Sat, Oct 06, 2018 at 11:31:04AM +0800, [email protected] wrote:
>>>>> On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote:
>>>>>>
>>>>>> From: Peng Hao <[email protected]>
>>>>>>
>>>>>> modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned
>>>>>>
>>>>>> Signed-off-by: Peng Hao <[email protected]>
>>>>>> ---
>>>>>> 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