Xen devel - Dec 2009 - [PATCH 01/02] pvrdtscp: move the place of write_rdtscp_aux()

Pvrdtscp: move write_rdtscp_aux() to paravirt_ctxt_switch_to()
 - Currently write_rdtscp_aux() is placed in update_vcpu_system_time(), which
is called by schedule() before context_switch(). This will break the HVM guest
TSC_AUX state because at this point, MSR hasn''t beed saved for HVM
guests.So
put the function in the point when a PV vcpu is really scheduled in. 

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>

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This patch is wrong for TSC_MODE_PVRDTSCP.  The original
code should be left in __update_vcpu_system_time and
the context switch code should write to TSC_AUX only
if tsc_mode is *NOT* TSC_MODE_PVRDTSCP because the
implementation of full rdtscp functionality and
TSC_MODE_PVRDTSCP mode are incompatible.

But I continue to question if this should be done at all.
See other thread.
> -----Original Message-----
> From: Xu, Dongxiao [mailto:dongxiao.xu@intel.com]
> Sent: Friday, December 11, 2009 4:54 AM
> To: xen-devel@lists.xensource.com
> Cc: Keir Fraser
> Subject: [Xen-devel][PATCH 01/02] pvrdtscp: move the place of
> write_rdtscp_aux()
> 
> 
>  Pvrdtscp: move write_rdtscp_aux() to paravirt_ctxt_switch_to()
>  - Currently write_rdtscp_aux() is placed in 
> update_vcpu_system_time(), which
> is called by schedule() before context_switch(). This will 
> break the HVM guest
> TSC_AUX state because at this point, MSR hasn''t beed saved 
> for HVM guests.So
> put the function in the point when a PV vcpu is really scheduled in. 
> 
> Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
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Dan Magenheimer wrote:
> This patch is wrong for TSC_MODE_PVRDTSCP.  The original
> code should be left in __update_vcpu_system_time and
> the context switch code should write to TSC_AUX only
> if tsc_mode is *NOT* TSC_MODE_PVRDTSCP because the
> implementation of full rdtscp functionality and
> TSC_MODE_PVRDTSCP mode are incompatible.
Could you detail the wrong place? Appreciate for this!
In my patch, I have done save/restore for guest/host 
TSC_AUX MSR, so it will not break PVRDTSC logic. 
 
> 
> But I continue to question if this should be done at all.
> See other thread.
> 
>> -----Original Message-----
>> From: Xu, Dongxiao [mailto:dongxiao.xu@intel.com]
>> Sent: Friday, December 11, 2009 4:54 AM
>> To: xen-devel@lists.xensource.com
>> Cc: Keir Fraser
>> Subject: [Xen-devel][PATCH 01/02] pvrdtscp: move the place of
>> write_rdtscp_aux() 
>> 
>> 
>>  Pvrdtscp: move write_rdtscp_aux() to paravirt_ctxt_switch_to()
>>  - Currently write_rdtscp_aux() is placed in
>> update_vcpu_system_time(), which
>> is called by schedule() before context_switch(). This will
>> break the HVM guest
>> TSC_AUX state because at this point, MSR hasn''t beed saved
>> for HVM guests.So
>> put the function in the point when a PV vcpu is really scheduled in.
>> 
>> Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
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I am OK with this patch [01/02] now (see other thread),
though still would like the discussion to continue
about the other patch [02/02].

Thanks,
Dan
> -----Original Message-----
> From: Xu, Dongxiao [mailto:dongxiao.xu@intel.com]
> Sent: Friday, December 11, 2009 8:31 AM
> To: Dan Magenheimer; xen-devel@lists.xensource.com
> Cc: Keir Fraser
> Subject: RE: [Xen-devel][PATCH 01/02] pvrdtscp: move the place of
> write_rdtscp_aux()
> 
> 
> Dan Magenheimer wrote:
> > This patch is wrong for TSC_MODE_PVRDTSCP.  The original
> > code should be left in __update_vcpu_system_time and
> > the context switch code should write to TSC_AUX only
> > if tsc_mode is *NOT* TSC_MODE_PVRDTSCP because the
> > implementation of full rdtscp functionality and
> > TSC_MODE_PVRDTSCP mode are incompatible.
> 
> Could you detail the wrong place? Appreciate for this!
> In my patch, I have done save/restore for guest/host 
> TSC_AUX MSR, so it will not break PVRDTSC logic. 
>  
> > 
> > But I continue to question if this should be done at all.
> > See other thread.
> > 
> >> -----Original Message-----
> >> From: Xu, Dongxiao [mailto:dongxiao.xu@intel.com]
> >> Sent: Friday, December 11, 2009 4:54 AM
> >> To: xen-devel@lists.xensource.com
> >> Cc: Keir Fraser
> >> Subject: [Xen-devel][PATCH 01/02] pvrdtscp: move the place of
> >> write_rdtscp_aux() 
> >> 
> >> 
> >>  Pvrdtscp: move write_rdtscp_aux() to paravirt_ctxt_switch_to()
> >>  - Currently write_rdtscp_aux() is placed in
> >> update_vcpu_system_time(), which
> >> is called by schedule() before context_switch(). This will
> >> break the HVM guest
> >> TSC_AUX state because at this point, MSR hasn''t beed
saved
> >> for HVM guests.So
> >> put the function in the point when a PV vcpu is really 
> scheduled in.
> >> 
> >> Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>
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