diff mbox series

KVM: Fix steal time asm constraints in 32-bit mode

Message ID 89bf72db1b859990355f9c40713a34e0d2d86c98.camel@infradead.org (mailing list archive)
State New, archived
Headers show
Series KVM: Fix steal time asm constraints in 32-bit mode | expand

Commit Message

David Woodhouse Nov. 14, 2021, 8:59 a.m. UTC 
From: David Woodhouse <dwmw@amazon.co.uk>

In 64-bit mode, x86 instruction encoding allows us to use the low 8 bits
of any GPR as an 8-bit operand. In 32-bit mode, however, we can only use
the [abcd] registers. For which, GCC has the "q" constraint instead of
the less restrictive "r".

Fixes: 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time / preempted status")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Paolo Bonzini Nov. 16, 2021, 9:46 a.m. UTC | #1 
On 11/14/21 09:59, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> In 64-bit mode, x86 instruction encoding allows us to use the low 8 bits
> of any GPR as an 8-bit operand. In 32-bit mode, however, we can only use
> the [abcd] registers. For which, GCC has the "q" constraint instead of
> the less restrictive "r".
> 
> Fixes: 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time / preempted status")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   arch/x86/kvm/x86.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8f156905ae38..0a689bb62e9e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3307,7 +3307,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
>   			     "xor %1, %1\n"
>   			     "2:\n"
>   			     _ASM_EXTABLE_UA(1b, 2b)
> -			     : "+r" (st_preempted),
> +			     : "+q" (st_preempted),
>   			       "+&r" (err)
>   			     : "m" (st->preempted));
>   		if (err)
> 

Queued with the addition of the "m" -> "+m" change, thanks.

Paolo
diff mbox series

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8f156905ae38..0a689bb62e9e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3307,7 +3307,7 @@  static void record_steal_time(struct kvm_vcpu *vcpu)
 			     "xor %1, %1\n"
 			     "2:\n"
 			     _ASM_EXTABLE_UA(1b, 2b)
-			     : "+r" (st_preempted),
+			     : "+q" (st_preempted),
 			       "+&r" (err)
 			     : "m" (st->preempted));
 		if (err)