[PATCH v2] KVM: arm64: fix compile error because of shift overflow

[PATCH v2] KVM: arm64: fix compile error because of shift overflow

[Yang Yingliang]

Using GENMASK() to generate the masks of device type and device id, it makes
code unambiguous, also it can fix the following fix compile error because of
shift overflow when using low verison gcc(mine version is 7.5):

In function ‘kvm_vm_ioctl_set_device_addr.isra.38’,
    inlined from ‘kvm_arch_vm_ioctl’ at arch/arm64/kvm/arm.c:1454:10:
././include/linux/compiler_types.h:354:38: error: call to ‘__compiletime_assert_599’ \
declared with attribute error: FIELD_GET: mask is not constant
  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

Fixes: 9f968c9266aa ("KVM: arm64: vgic-v2: Add helper for legacy dist/cpuif base address setting")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
---
v2:
  Using GENMASK() to generate the masks.
---
 arch/arm64/include/uapi/asm/kvm.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 3bb134355874..5e7dfaf76ec1 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -75,9 +75,9 @@ struct kvm_regs {
 
 /* KVM_ARM_SET_DEVICE_ADDR ioctl id encoding */
 #define KVM_ARM_DEVICE_TYPE_SHIFT	0
-#define KVM_ARM_DEVICE_TYPE_MASK	(0xffff << KVM_ARM_DEVICE_TYPE_SHIFT)
+#define KVM_ARM_DEVICE_TYPE_MASK	GENMASK(15, KVM_ARM_DEVICE_TYPE_SHIFT)
 #define KVM_ARM_DEVICE_ID_SHIFT		16
-#define KVM_ARM_DEVICE_ID_MASK		(0xffff << KVM_ARM_DEVICE_ID_SHIFT)
+#define KVM_ARM_DEVICE_ID_MASK		GENMASK(31, KVM_ARM_DEVICE_ID_SHIFT)
 
 /* Supported device IDs */
 #define KVM_ARM_DEVICE_VGIC_V2		0
-- 
2.25.1


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Re: [PATCH v2] KVM: arm64: fix compile error because of shift overflow

[Marc Zyngier]

On Tue, 09 Aug 2022 14:51:27 +0100,
Yang Yingliang <yangyingliang@huawei.com> wrote:
> 
> Using GENMASK() to generate the masks of device type and device id, it makes
> code unambiguous, also it can fix the following fix compile error because of
> shift overflow when using low verison gcc(mine version is 7.5):
> 
> In function ‘kvm_vm_ioctl_set_device_addr.isra.38’,
>     inlined from ‘kvm_arch_vm_ioctl’ at arch/arm64/kvm/arm.c:1454:10:
> ././include/linux/compiler_types.h:354:38: error: call to ‘__compiletime_assert_599’ \
> declared with attribute error: FIELD_GET: mask is not constant
>   _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
> 
> Fixes: 9f968c9266aa ("KVM: arm64: vgic-v2: Add helper for legacy dist/cpuif base address setting")
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ---
> v2:
>   Using GENMASK() to generate the masks.
> ---
>  arch/arm64/include/uapi/asm/kvm.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 3bb134355874..5e7dfaf76ec1 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -75,9 +75,9 @@ struct kvm_regs {
>  
>  /* KVM_ARM_SET_DEVICE_ADDR ioctl id encoding */
>  #define KVM_ARM_DEVICE_TYPE_SHIFT	0
> -#define KVM_ARM_DEVICE_TYPE_MASK	(0xffff << KVM_ARM_DEVICE_TYPE_SHIFT)
> +#define KVM_ARM_DEVICE_TYPE_MASK	GENMASK(15, KVM_ARM_DEVICE_TYPE_SHIFT)
>  #define KVM_ARM_DEVICE_ID_SHIFT		16
> -#define KVM_ARM_DEVICE_ID_MASK		(0xffff << KVM_ARM_DEVICE_ID_SHIFT)
> +#define KVM_ARM_DEVICE_ID_MASK		GENMASK(31, KVM_ARM_DEVICE_ID_SHIFT)
>  
>  /* Supported device IDs */
>  #define KVM_ARM_DEVICE_VGIC_V2		0

This is marginally better, but what I was expecting is something like:

#define KVM_ARM_DEVICE_ID_MASK	GENMASK(KVM_ARM_DEVICE_ID_SHIFT + 15, \
					KVM_ARM_DEVICE_ID_SHIFT)

which I find a bit more readable.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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