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[Xen-devel] reading IOPL

  • To: "xen-devel" <xen-devel@xxxxxxxxxxxxx>
  • From: "Jan Beulich" <JBeulich@xxxxxxxx>
  • Date: Thu, 03 May 2012 17:07:04 +0100
  • Delivery-date: Thu, 03 May 2012 16:07:24 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

Both Linux and Xen offer only ways to set the IOPL. While on native Linux
this is not a problem since user mode code can read the IOPL by inspecting
EFLAGS, on Xen this would always yield zero.

Now X folks appear to be using save-modify-restore cycles in some newer
code, and this obviously breaks under Xen, as they would restore IOPL 0
even when IOPL 3 was in effect before.

Since the only way to read the IOPL is xc_vcpu_getcontext() (i.e.
XEN_DOMCTL_getvcpucontext), I wonder whether we shouldn't add
e.g. a "get" counterpart to PHYSDEVOP_set_iopl.

Or am I overlooking some other access mechanism?


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