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RE: [Xen-devel][PATCH 01/02] pvrdtscp: move the place of write_rdtscp_au

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel][PATCH 01/02] pvrdtscp: move the place of write_rdtscp_aux()
From: "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>
Date: Fri, 11 Dec 2009 23:31:24 +0800
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Cc: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Thread-topic: [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@xxxxxxxxx]
>> Sent: Friday, December 11, 2009 4:54 AM
>> To: xen-devel@xxxxxxxxxxxxxxxxxxx
>> 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@xxxxxxxxx>
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