Xen devel - Mar 2010 - set_msi_affinity() vs. pci_restore_msi_state()

Isn''t the fact that the former updates the MSI message data without
updating the copy of it in memory a problem for the latter, i.e. won''t
the latter restore stale information? While the problem (if there is one)
existed before c/s 20073, the fact that the vector now can change
seems to make the potential effect of this much worse.

Thanks, Jan


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Jan, 
    Have you met any issue ?  Per my understanding, there is no problem here. 
For set_msi_affinity, it calls write_msi_msg to write the MSI info to real
hardware and also update it to (msi_desc)entry->msg, so entry->msg should
store the latest msi''s data/addr. And only if pci_restore_msi_state
uses entry->msg to restore msi state, the correct info should be restored.
And the key point is that write_msi_msg not only update hardware''s msi
state, but it stores the latest MSI info to msi descriptor entry->msg.
Xiantao

-----Original Message-----
From: Jan Beulich [mailto:JBeulich@novell.com] 
Sent: Saturday, March 06, 2010 12:04 AM
To: Zhang, Xiantao
Cc: xen-devel@lists.xensource.com
Subject: set_msi_affinity() vs. pci_restore_msi_state()

Isn''t the fact that the former updates the MSI message data without
updating the copy of it in memory a problem for the latter, i.e. won''t
the latter restore stale information? While the problem (if there is one)
existed before c/s 20073, the fact that the vector now can change
seems to make the potential effect of this much worse.

Thanks, Jan


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Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

>>> "Zhang, Xiantao" <xiantao.zhang@intel.com> 08.03.10
03:14 >>>
>Jan, 
>    Have you met any issue ?
Yes, but not in the resume code path. Instead, I got a log including
output from the new ''M'' debug key, which showed that
entry->msg.data
must have been all zero. That lead me to look at the code paths where
this field would get written.
>Per my understanding, there is no problem here.  For set_msi_affinity,
>it calls write_msi_msg to write the MSI info to real hardware and also
update it to (msi_desc)entry->msg, so entry->msg should store
the
>latest msi''s data/addr.
Oh, right, I overlooked write_msi_msg() writing entry->msg - mislead
by the fact that it may be called with &entry->msg (which makes the
 - in this case unnecessary - assignment sort of unexpected.

Jan


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