[v3,2/2] KVM: make crash_clear_loaded_vmcss valid when loading kvm_intel module

Commit Message

Yanfei Zhang Oct. 31, 2012, 3:34 a.m. UTC

Signed-off-by: Zhang Yanfei <[e-mail]>
---
 arch/x86/kvm/vmx.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

Comments

Daisuke HATAYAMA Oct. 31, 2012, 9:01 a.m. UTC | #1

> -----Original Message-----
> From: [e-mail]
> [mailto:[e-mail]] On Behalf Of zhangyanfei
> Sent: Wednesday, October 31, 2012 12:34 PM
> To: [e-mail]; [e-mail]; Avi Kivity; Marcelo
> Tosatti
> Cc: [e-mail]; [e-mail]
> Subject: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
> loading kvm_intel module
> 
> Signed-off-by: Zhang Yanfei <[e-mail]>

[...]

> @@ -7230,6 +7231,10 @@ static int __init vmx_init(void)
>  	if (r)
>  		goto out3;
> 
> +#ifdef CONFIG_KEXEC
> +	crash_clear_loaded_vmcss = vmclear_local_loaded_vmcss;
> +#endif
> +

Assignment here cannot cover the case where NMI is initiated after VMX is on in kvm_init and before vmclear_local_loaded_vmcss is assigned, though rare but can happen.

What does happen if calling vmclear_local_loaded_vmcss before kvm_init? I think it no problem since the list is initially empty.

>  	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
>  	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
>  	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
> @@ -7265,6 +7270,10 @@ static void __exit vmx_exit(void)
>  	free_page((unsigned long)vmx_io_bitmap_b);
>  	free_page((unsigned long)vmx_io_bitmap_a);
> 
> +#ifdef CONFIG_KEXEC
> +	crash_clear_loaded_vmcss = NULL;
> +#endif
> +
>  	kvm_exit();
>  }

Also, this is converse to the above.

Thanks.
HATAYAMA, Daisuke

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Yanfei Zhang Nov. 1, 2012, 5:55 a.m. UTC | #2

? 2012?10?31? 17:01, Hatayama, Daisuke ??:
> 
> 
>> -----Original Message-----
>> From: [e-mail]
>> [mailto:[e-mail]] On Behalf Of zhangyanfei
>> Sent: Wednesday, October 31, 2012 12:34 PM
>> To: [e-mail]; [e-mail]; Avi Kivity; Marcelo
>> Tosatti
>> Cc: [e-mail]; [e-mail]
>> Subject: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
>> loading kvm_intel module
>>
>> Signed-off-by: Zhang Yanfei <[e-mail]>
> 
> [...]
> 
>> @@ -7230,6 +7231,10 @@ static int __init vmx_init(void)
>>  	if (r)
>>  		goto out3;
>>
>> +#ifdef CONFIG_KEXEC
>> +	crash_clear_loaded_vmcss = vmclear_local_loaded_vmcss;
>> +#endif
>> +
> 
> Assignment here cannot cover the case where NMI is initiated after VMX is on in kvm_init and before vmclear_local_loaded_vmcss is assigned, though rare but can happen.
> 

By saying "VMX is on in kvm init", you mean kvm_init enables the VMX feature in the logical processor?
No, only there is a vcpu to be created, kvm will enable the VMX feature.

I think there is no difference with this assignment before or after kvm_init because the vmcs linked
list must be empty before vmx_init is finished.

Thanks
Zhang Yanfei

> What does happen if calling vmclear_local_loaded_vmcss before kvm_init? I think it no problem since the list is initially empty.
> 
>>  	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
>>  	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
>>  	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
>> @@ -7265,6 +7270,10 @@ static void __exit vmx_exit(void)
>>  	free_page((unsigned long)vmx_io_bitmap_b);
>>  	free_page((unsigned long)vmx_io_bitmap_a);
>>
>> +#ifdef CONFIG_KEXEC
>> +	crash_clear_loaded_vmcss = NULL;
>> +#endif
>> +
>>  	kvm_exit();
>>  }
> 
> Also, this is converse to the above.
> 
> Thanks.
> HATAYAMA, Daisuke
> 
> 

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Marcelo Tosatti Nov. 13, 2012, 9:22 p.m. UTC | #3

On Thu, Nov 01, 2012 at 01:55:04PM +0800, zhangyanfei wrote:
> ? 2012?10?31? 17:01, Hatayama, Daisuke ??:
> > 
> > 
> >> -----Original Message-----
> >> From: [e-mail]
> >> [mailto:[e-mail]] On Behalf Of zhangyanfei
> >> Sent: Wednesday, October 31, 2012 12:34 PM
> >> To: [e-mail]; [e-mail]; Avi Kivity; Marcelo
> >> Tosatti
> >> Cc: [e-mail]; [e-mail]
> >> Subject: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
> >> loading kvm_intel module
> >>
> >> Signed-off-by: Zhang Yanfei <[e-mail]>
> > 
> > [...]
> > 
> >> @@ -7230,6 +7231,10 @@ static int __init vmx_init(void)
> >>  	if (r)
> >>  		goto out3;
> >>
> >> +#ifdef CONFIG_KEXEC
> >> +	crash_clear_loaded_vmcss = vmclear_local_loaded_vmcss;
> >> +#endif
> >> +
> > 
> > Assignment here cannot cover the case where NMI is initiated after VMX is on in kvm_init and before vmclear_local_loaded_vmcss is assigned, though rare but can happen.
> > 
> 
> By saying "VMX is on in kvm init", you mean kvm_init enables the VMX feature in the logical processor?
> No, only there is a vcpu to be created, kvm will enable the VMX feature.
> 
> I think there is no difference with this assignment before or after kvm_init because the vmcs linked
> list must be empty before vmx_init is finished.

The list is not initialized before hardware_enable(), though. Should
move the assignment after that.

Also, it is possible that the loaded_vmcss_on_cpu list is being modified
_while_ crash executes say via NMI, correct? If that is the case, better
flag that the list is under manipulation so the vmclear can be skipped.

> Thanks
> Zhang Yanfei
> 
> > What does happen if calling vmclear_local_loaded_vmcss before kvm_init? I think it no problem since the list is initially empty.
> > 
> >>  	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
> >>  	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
> >>  	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
> >> @@ -7265,6 +7270,10 @@ static void __exit vmx_exit(void)
> >>  	free_page((unsigned long)vmx_io_bitmap_b);
> >>  	free_page((unsigned long)vmx_io_bitmap_a);
> >>
> >> +#ifdef CONFIG_KEXEC
> >> +	crash_clear_loaded_vmcss = NULL;
> >> +#endif
> >> +
> >>  	kvm_exit();
> >>  }
> > 
> > Also, this is converse to the above.
> > 
> > Thanks.
> > HATAYAMA, Daisuke
> > 
> > 
> 
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Yanfei Zhang Nov. 14, 2012, 9:13 a.m. UTC | #4

? 2012?11?14? 05:22, Marcelo Tosatti ??:
> On Thu, Nov 01, 2012 at 01:55:04PM +0800, zhangyanfei wrote:
>> ? 2012?10?31? 17:01, Hatayama, Daisuke ??:
>>>
>>>
>>>> -----Original Message-----
>>>> From: [e-mail]
>>>> [mailto:[e-mail]] On Behalf Of zhangyanfei
>>>> Sent: Wednesday, October 31, 2012 12:34 PM
>>>> To: [e-mail]; [e-mail]; Avi Kivity; Marcelo
>>>> Tosatti
>>>> Cc: [e-mail]; [e-mail]
>>>> Subject: [PATCH v3 2/2] KVM: make crash_clear_loaded_vmcss valid when
>>>> loading kvm_intel module
>>>>
>>>> Signed-off-by: Zhang Yanfei <[e-mail]>
>>>
>>> [...]
>>>
>>>> @@ -7230,6 +7231,10 @@ static int __init vmx_init(void)
>>>>  	if (r)
>>>>  		goto out3;
>>>>
>>>> +#ifdef CONFIG_KEXEC
>>>> +	crash_clear_loaded_vmcss = vmclear_local_loaded_vmcss;
>>>> +#endif
>>>> +
>>>
>>> Assignment here cannot cover the case where NMI is initiated after VMX is on in kvm_init and before vmclear_local_loaded_vmcss is assigned, though rare but can happen.
>>>
>>
>> By saying "VMX is on in kvm init", you mean kvm_init enables the VMX feature in the logical processor?
>> No, only there is a vcpu to be created, kvm will enable the VMX feature.
>>
>> I think there is no difference with this assignment before or after kvm_init because the vmcs linked
>> list must be empty before vmx_init is finished.
> 
> The list is not initialized before hardware_enable(), though. Should
> move the assignment after that.
> 
> Also, it is possible that the loaded_vmcss_on_cpu list is being modified
> _while_ crash executes say via NMI, correct? If that is the case, better
> flag that the list is under manipulation so the vmclear can be skipped.
> 

Thanks for your comments.
In the new patchset, I didn't move the crash_clear_loaded_vmcss assignment.
I added a new percpu variable vmclear_skipped to indicate everything:
1. Before the loaded_vmcss_on_cpu list is initialized, vmclear_skipped is 1 and
   this means if the machine crashes and doing kdump, crash_clear_loaded_vmcss
   still will not be called.
2. If the loaded_vmcss_on_cpu list is under manipulation, vmclear_skipped is
   set to 1 and after the manipulation is finished, the variable is set to 0.
3. After all loaded vmcss are vmcleared, vmclear_skipped is set to 1. So we
   needn't repeat to vmclear loaded vmcss in kdump path.

Please refer to the new version of the patchset I sent. If you have any suggestions, that'll be helpful.

Thanks
Zhang

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Patch

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4ff0ab9..f6a16b2 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -41,6 +41,7 @@ 
 #include <asm/i387.h>
 #include <asm/xcr.h>
 #include <asm/perf_event.h>
+#include <asm/kexec.h>
 
 #include "trace.h"
 
@@ -7230,6 +7231,10 @@  static int __init vmx_init(void)
 	if (r)
 		goto out3;
 
+#ifdef CONFIG_KEXEC
+	crash_clear_loaded_vmcss = vmclear_local_loaded_vmcss;
+#endif
+
 	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
 	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
 	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
@@ -7265,6 +7270,10 @@  static void __exit vmx_exit(void)
 	free_page((unsigned long)vmx_io_bitmap_b);
 	free_page((unsigned long)vmx_io_bitmap_a);
 
+#ifdef CONFIG_KEXEC
+	crash_clear_loaded_vmcss = NULL;
+#endif
+
 	kvm_exit();
 }