[PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

[PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

[Sean Christopherson]

Explicitly cast the integer literal to an unsigned long when stuffing a
non-canonical value into the host virtual address during private memslot
deletion.  The explicit cast fixes a warning that gets promoted to an
error when running with KVM's newfangled -Werror setting.

  arch/x86/kvm/x86.c:9739:9: error: large integer implicitly truncated
  to unsigned type [-Werror=overflow]

Fixes: a3e967c0b87d3 ("KVM: Terminate memslot walks via used_slots"
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/x86.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ba4d476b79ad..fa03f31ab33c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9735,8 +9735,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 		if (!slot || !slot->npages)
 			return 0;
 
-		/* Stuff a non-canonical value to catch use-after-delete. */
-		hva = 0xdeadull << 48;
+		/*
+		 * Stuff a non-canonical value to catch use-after-delete.  This
+		 * ends up being 0 on 32-bit KVM, but there's no better
+		 * alternative.
+		 */
+		hva = (unsigned long)(0xdeadull << 48);
 		old_npages = slot->npages;
 	}
 
-- 
2.24.1

Re: [PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

[Vitaly Kuznetsov]

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Explicitly cast the integer literal to an unsigned long when stuffing a
> non-canonical value into the host virtual address during private memslot
> deletion.  The explicit cast fixes a warning that gets promoted to an
> error when running with KVM's newfangled -Werror setting.
>
>   arch/x86/kvm/x86.c:9739:9: error: large integer implicitly truncated
>   to unsigned type [-Werror=overflow]
>
> Fixes: a3e967c0b87d3 ("KVM: Terminate memslot walks via used_slots"

Missing ')'

> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/x86.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ba4d476b79ad..fa03f31ab33c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9735,8 +9735,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
>  		if (!slot || !slot->npages)
>  			return 0;
>  
> -		/* Stuff a non-canonical value to catch use-after-delete. */
> -		hva = 0xdeadull << 48;
> +		/*
> +		 * Stuff a non-canonical value to catch use-after-delete.  This
> +		 * ends up being 0 on 32-bit KVM, but there's no better
> +		 * alternative.
> +		 */
> +		hva = (unsigned long)(0xdeadull << 48);
>  		old_npages = slot->npages;
>  	}

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly

Re: [PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

[Paolo Bonzini]

On 05/03/20 01:24, Sean Christopherson wrote:
> Explicitly cast the integer literal to an unsigned long when stuffing a
> non-canonical value into the host virtual address during private memslot
> deletion.  The explicit cast fixes a warning that gets promoted to an
> error when running with KVM's newfangled -Werror setting.
> 
>   arch/x86/kvm/x86.c:9739:9: error: large integer implicitly truncated
>   to unsigned type [-Werror=overflow]
> 
> Fixes: a3e967c0b87d3 ("KVM: Terminate memslot walks via used_slots"
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/x86.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ba4d476b79ad..fa03f31ab33c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9735,8 +9735,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
>  		if (!slot || !slot->npages)
>  			return 0;
>  
> -		/* Stuff a non-canonical value to catch use-after-delete. */
> -		hva = 0xdeadull << 48;
> +		/*
> +		 * Stuff a non-canonical value to catch use-after-delete.  This
> +		 * ends up being 0 on 32-bit KVM, but there's no better
> +		 * alternative.
> +		 */
> +		hva = (unsigned long)(0xdeadull << 48);
>  		old_npages = slot->npages;
>  	}
>  
> 

Queued, thanks.

Paolo

Re: [PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

[Sean Christopherson]

On Thu, Mar 05, 2020 at 11:00:20AM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@intel.com> writes:
> 
> > Explicitly cast the integer literal to an unsigned long when stuffing a
> > non-canonical value into the host virtual address during private memslot
> > deletion.  The explicit cast fixes a warning that gets promoted to an
> > error when running with KVM's newfangled -Werror setting.
> >
> >   arch/x86/kvm/x86.c:9739:9: error: large integer implicitly truncated
> >   to unsigned type [-Werror=overflow]
> >
> > Fixes: a3e967c0b87d3 ("KVM: Terminate memslot walks via used_slots"
> 
> Missing ')'

Hrm, surprised checkpatch didn't catch that.