Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1230813 > unrolled thread

Re: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR"

Started byMarcelo Tosatti <mtosatti@redhat.com>
First post2015-09-22 21:10 +0200
Last post2015-09-24 02:10 +0200
Articles 3 — 2 participants

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0  initializes kvmclock system MSR" Marcelo Tosatti <mtosatti@redhat.com> - 2015-09-22 21:10 +0200
    Re: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0  initializes kvmclock system MSR" Paolo Bonzini <pbonzini@redhat.com> - 2015-09-22 22:00 +0200
      Re: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0  initializes kvmclock system MSR" Marcelo Tosatti <mtosatti@redhat.com> - 2015-09-24 02:10 +0200

#1230813 — Re: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR"

FromMarcelo Tosatti <mtosatti@redhat.com>
Date2015-09-22 21:10 +0200
SubjectRe: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR"
Message-ID<qbB6X-5Uu-59@gated-at.bofh.it>
On Fri, Sep 18, 2015 at 05:54:30PM +0200, Radim Krčmář wrote:
> Shifting pvclock_vcpu_time_info.system_time on write to KVM system time
> MSR is a change of ABI.  Probably only 2.6.16 based SLES 10 breaks due
> to its custom enhancements to kvmclock, but KVM never declared the MSR
> only for one-shot initialization.  (Doc says that only one write is
> needed.)
> 
> This reverts commit b7e60c5aedd2b63f16ef06fde4f81ca032211bc5.
> And adds a note to the definition of PVCLOCK_COUNTS_FROM_ZERO.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  arch/x86/include/asm/pvclock-abi.h | 1 +
>  arch/x86/kvm/x86.c                 | 4 ----
>  2 files changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
> index 655e07a48f6c..67f08230103a 100644
> --- a/arch/x86/include/asm/pvclock-abi.h
> +++ b/arch/x86/include/asm/pvclock-abi.h
> @@ -41,6 +41,7 @@ struct pvclock_wall_clock {
>  
>  #define PVCLOCK_TSC_STABLE_BIT	(1 << 0)
>  #define PVCLOCK_GUEST_STOPPED	(1 << 1)
> +/* PVCLOCK_COUNTS_FROM_ZERO broke ABI and can't be used anymore. */
>  #define PVCLOCK_COUNTS_FROM_ZERO (1 << 2)
>  #endif /* __ASSEMBLY__ */
>  #endif /* _ASM_X86_PVCLOCK_ABI_H */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 18d59b584dee..34d33f4757d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1707,8 +1707,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>  		vcpu->pvclock_set_guest_stopped_request = false;
>  	}
>  
> -	pvclock_flags |= PVCLOCK_COUNTS_FROM_ZERO;
> -
>  	/* If the host uses TSC clocksource, then it is stable */
>  	if (use_master_clock)
>  		pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
> @@ -2006,8 +2004,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  					&vcpu->requests);
>  
>  			ka->boot_vcpu_runs_old_kvmclock = tmp;
> -
> -			ka->kvmclock_offset = -get_kernel_ns();
>  		}
>  
>  		vcpu->arch.time = data;
> -- 
> 2.5.2

ACK

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1230896

FromPaolo Bonzini <pbonzini@redhat.com>
Date2015-09-22 22:00 +0200
Message-ID<qbBTk-6Qf-19@gated-at.bofh.it>
In reply to#1230813

On 22/09/2015 21:01, Marcelo Tosatti wrote:
> On Fri, Sep 18, 2015 at 05:54:30PM +0200, Radim Krčmář wrote:
>> Shifting pvclock_vcpu_time_info.system_time on write to KVM system time
>> MSR is a change of ABI.  Probably only 2.6.16 based SLES 10 breaks due
>> to its custom enhancements to kvmclock, but KVM never declared the MSR
>> only for one-shot initialization.  (Doc says that only one write is
>> needed.)
>>
>> This reverts commit b7e60c5aedd2b63f16ef06fde4f81ca032211bc5.
>> And adds a note to the definition of PVCLOCK_COUNTS_FROM_ZERO.
>>
>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>> ---
>>  arch/x86/include/asm/pvclock-abi.h | 1 +
>>  arch/x86/kvm/x86.c                 | 4 ----
>>  2 files changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
>> index 655e07a48f6c..67f08230103a 100644
>> --- a/arch/x86/include/asm/pvclock-abi.h
>> +++ b/arch/x86/include/asm/pvclock-abi.h
>> @@ -41,6 +41,7 @@ struct pvclock_wall_clock {
>>  
>>  #define PVCLOCK_TSC_STABLE_BIT	(1 << 0)
>>  #define PVCLOCK_GUEST_STOPPED	(1 << 1)
>> +/* PVCLOCK_COUNTS_FROM_ZERO broke ABI and can't be used anymore. */
>>  #define PVCLOCK_COUNTS_FROM_ZERO (1 << 2)
>>  #endif /* __ASSEMBLY__ */
>>  #endif /* _ASM_X86_PVCLOCK_ABI_H */
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 18d59b584dee..34d33f4757d2 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1707,8 +1707,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>>  		vcpu->pvclock_set_guest_stopped_request = false;
>>  	}
>>  
>> -	pvclock_flags |= PVCLOCK_COUNTS_FROM_ZERO;
>> -
>>  	/* If the host uses TSC clocksource, then it is stable */
>>  	if (use_master_clock)
>>  		pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
>> @@ -2006,8 +2004,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  					&vcpu->requests);
>>  
>>  			ka->boot_vcpu_runs_old_kvmclock = tmp;
>> -
>> -			ka->kvmclock_offset = -get_kernel_ns();
>>  		}
>>  
>>  		vcpu->arch.time = data;
>> -- 
>> 2.5.2
> 
> ACK

So I suppose you changed your mind :) but can you explain the reasoning?

Paolo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1231790

FromMarcelo Tosatti <mtosatti@redhat.com>
Date2015-09-24 02:10 +0200
Message-ID<qc2gO-3eb-1@gated-at.bofh.it>
In reply to#1230896
On Tue, Sep 22, 2015 at 09:52:49PM +0200, Paolo Bonzini wrote:
> 
> 
> On 22/09/2015 21:01, Marcelo Tosatti wrote:
> > On Fri, Sep 18, 2015 at 05:54:30PM +0200, Radim Krčmář wrote:
> >> Shifting pvclock_vcpu_time_info.system_time on write to KVM system time
> >> MSR is a change of ABI.  Probably only 2.6.16 based SLES 10 breaks due
> >> to its custom enhancements to kvmclock, but KVM never declared the MSR
> >> only for one-shot initialization.  (Doc says that only one write is
> >> needed.)
> >>
> >> This reverts commit b7e60c5aedd2b63f16ef06fde4f81ca032211bc5.
> >> And adds a note to the definition of PVCLOCK_COUNTS_FROM_ZERO.
> >>
> >> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> >> ---
> >>  arch/x86/include/asm/pvclock-abi.h | 1 +
> >>  arch/x86/kvm/x86.c                 | 4 ----
> >>  2 files changed, 1 insertion(+), 4 deletions(-)
> >>
> >> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
> >> index 655e07a48f6c..67f08230103a 100644
> >> --- a/arch/x86/include/asm/pvclock-abi.h
> >> +++ b/arch/x86/include/asm/pvclock-abi.h
> >> @@ -41,6 +41,7 @@ struct pvclock_wall_clock {
> >>  
> >>  #define PVCLOCK_TSC_STABLE_BIT	(1 << 0)
> >>  #define PVCLOCK_GUEST_STOPPED	(1 << 1)
> >> +/* PVCLOCK_COUNTS_FROM_ZERO broke ABI and can't be used anymore. */
> >>  #define PVCLOCK_COUNTS_FROM_ZERO (1 << 2)
> >>  #endif /* __ASSEMBLY__ */
> >>  #endif /* _ASM_X86_PVCLOCK_ABI_H */
> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >> index 18d59b584dee..34d33f4757d2 100644
> >> --- a/arch/x86/kvm/x86.c
> >> +++ b/arch/x86/kvm/x86.c
> >> @@ -1707,8 +1707,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> >>  		vcpu->pvclock_set_guest_stopped_request = false;
> >>  	}
> >>  
> >> -	pvclock_flags |= PVCLOCK_COUNTS_FROM_ZERO;
> >> -
> >>  	/* If the host uses TSC clocksource, then it is stable */
> >>  	if (use_master_clock)
> >>  		pvclock_flags |= PVCLOCK_TSC_STABLE_BIT;
> >> @@ -2006,8 +2004,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >>  					&vcpu->requests);
> >>  
> >>  			ka->boot_vcpu_runs_old_kvmclock = tmp;
> >> -
> >> -			ka->kvmclock_offset = -get_kernel_ns();
> >>  		}
> >>  
> >>  		vcpu->arch.time = data;
> >> -- 
> >> 2.5.2
> > 
> > ACK
> 
> So I suppose you changed your mind :) but can you explain the reasoning?
> 
> Paolo

The patch is correct. Overflow (issue raised) is only an issue 
without PVCLOCK_TSC_STABLE_BIT.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web