Re: [PATCH] kvm:x86:Fix error handling in the function kvm_lapic_sync_to_vapic

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/08/2015 21:26, Nicholas Krause wrote:
> This fixes error handling in the function kvm_lapic_sync_to_vapic
> to check the value of the call to kvm_write_guest_cached to see if
> it failed by returning a error code and if so execute WARN_ON to
> allow the user to see in their logs the failure when executing the
> function kvm_lapic_sync_to_vapic.
> 
> Signed-off-by: Nicholas Krause <xerofoify@gmail.com>
> ---
>  arch/x86/kvm/lapic.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 2a5ca97..f3946c0 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1935,7 +1935,7 @@ static void apic_sync_pv_eoi_to_guest(struct kvm_vcpu *vcpu,
>  void kvm_lapic_sync_to_vapic(struct kvm_vcpu *vcpu)
>  {
>  	u32 data, tpr;
> -	int max_irr, max_isr;
> +	int max_irr, max_isr, ret;
>  	struct kvm_lapic *apic = vcpu->arch.apic;
>  
>  	apic_sync_pv_eoi_to_guest(vcpu, apic);
> @@ -1952,8 +1952,9 @@ void kvm_lapic_sync_to_vapic(struct kvm_vcpu *vcpu)
>  		max_isr = 0;
>  	data = (tpr & 0xff) | ((max_isr & 0xf0) << 8) | (max_irr << 24);
>  
> -	kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.apic->vapic_cache, &data,
> -				sizeof(u32));
> +	ret = kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.apic->vapic_cache, &data,
> +				     sizeof(u32));
> +	WARN_ON(ret);
>  }
>  
>  int kvm_lapic_set_vapic_addr(struct kvm_vcpu *vcpu, gpa_t vapic_addr)
> 

It shouldn't happen, but I cannot rule out that a guest cannot trigger
it.  It would be a bug or bad behavior in the guest but, if it can, a
WARN message in the host dmesg would not be the right thing to do.

So I prefer to leave the return value unchecked.

Paolo