* [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero
@ 2020-02-07 23:18 Colin King
2020-02-08 0:47 ` Sean Christopherson
0 siblings, 1 reply; 4+ messages in thread
From: Colin King @ 2020-02-07 23:18 UTC (permalink / raw)
To: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, H . Peter Anvin, x86, kvm
Cc: kernel-janitors, linux-kernel
From: Colin Ian King <colin.king@canonical.com>
The check cpu->hv_clock.system_time < 0 is redundant since system_time
is a u64 and hence can never be less than zero. Remove it.
Addresses-Coverity: ("Macro compares unsigned to 0")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
arch/x86/kvm/x86.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fbabb2f06273..d4967ac47e68 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2448,7 +2448,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
vcpu->last_guest_tsc = tsc_timestamp;
- WARN_ON(vcpu->hv_clock.system_time < 0);
/* If the host uses TSC clocksource, then it is stable */
pvclock_flags = 0;
--
2.24.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero
2020-02-07 23:18 [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero Colin King
@ 2020-02-08 0:47 ` Sean Christopherson
2020-02-08 12:09 ` Colin Ian King
2020-02-12 12:32 ` Paolo Bonzini
0 siblings, 2 replies; 4+ messages in thread
From: Sean Christopherson @ 2020-02-08 0:47 UTC (permalink / raw)
To: Colin King
Cc: Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, x86, kvm, kernel-janitors, linux-kernel
On Fri, Feb 07, 2020 at 11:18:13PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> The check cpu->hv_clock.system_time < 0 is redundant since system_time
> is a u64 and hence can never be less than zero. Remove it.
>
> Addresses-Coverity: ("Macro compares unsigned to 0")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
> arch/x86/kvm/x86.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fbabb2f06273..d4967ac47e68 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2448,7 +2448,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
> vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
> vcpu->last_guest_tsc = tsc_timestamp;
> - WARN_ON(vcpu->hv_clock.system_time < 0);
Don't know this code well, but @kernel_ns and @v->kvm->arch.kvmclock_offset
are both s64, so maybe this was intended and/or desirable?
WARN_ON((s64)vcpu->hv_clock.system_time < 0);
> /* If the host uses TSC clocksource, then it is stable */
> pvclock_flags = 0;
> --
> 2.24.0
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero
2020-02-08 0:47 ` Sean Christopherson
@ 2020-02-08 12:09 ` Colin Ian King
2020-02-12 12:32 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Colin Ian King @ 2020-02-08 12:09 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, x86, kvm, kernel-janitors, linux-kernel
On 08/02/2020 00:47, Sean Christopherson wrote:
> On Fri, Feb 07, 2020 at 11:18:13PM +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> The check cpu->hv_clock.system_time < 0 is redundant since system_time
>> is a u64 and hence can never be less than zero. Remove it.
>>
>> Addresses-Coverity: ("Macro compares unsigned to 0")
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>> arch/x86/kvm/x86.c | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index fbabb2f06273..d4967ac47e68 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2448,7 +2448,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>> vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
>> vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
>> vcpu->last_guest_tsc = tsc_timestamp;
>> - WARN_ON(vcpu->hv_clock.system_time < 0);
>
> Don't know this code well, but @kernel_ns and @v->kvm->arch.kvmclock_offset
> are both s64, so maybe this was intended and/or desirable?
Something is definitely not correct for sure.
>
> WARN_ON((s64)vcpu->hv_clock.system_time < 0);
>
>
>> /* If the host uses TSC clocksource, then it is stable */
>> pvclock_flags = 0;
>> --
>> 2.24.0
>>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero
2020-02-08 0:47 ` Sean Christopherson
2020-02-08 12:09 ` Colin Ian King
@ 2020-02-12 12:32 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2020-02-12 12:32 UTC (permalink / raw)
To: Sean Christopherson, Colin King
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, H . Peter Anvin,
x86, kvm, kernel-janitors, linux-kernel
On 08/02/20 01:47, Sean Christopherson wrote:
> On Fri, Feb 07, 2020 at 11:18:13PM +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> The check cpu->hv_clock.system_time < 0 is redundant since system_time
>> is a u64 and hence can never be less than zero. Remove it.
>>
>> Addresses-Coverity: ("Macro compares unsigned to 0")
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>> arch/x86/kvm/x86.c | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index fbabb2f06273..d4967ac47e68 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2448,7 +2448,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>> vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
>> vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
>> vcpu->last_guest_tsc = tsc_timestamp;
>> - WARN_ON(vcpu->hv_clock.system_time < 0);
>
> Don't know this code well, but @kernel_ns and @v->kvm->arch.kvmclock_offset
> are both s64, so maybe this was intended and/or desirable?
>
> WARN_ON((s64)vcpu->hv_clock.system_time < 0);
Yes, that's related to the bugfix where kvmclock would get negative. I
queued the patch with the (s64) cast added. Thanks to both of you!
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-02-12 12:32 UTC | newest]
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2020-02-07 23:18 [PATCH][next] KVM: x86: remove redundant WARN_ON check of an unsigned less than zero Colin King
2020-02-08 0:47 ` Sean Christopherson
2020-02-08 12:09 ` Colin Ian King
2020-02-12 12:32 ` Paolo Bonzini
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