Messages in this thread | | | Date | Tue, 26 Aug 2008 12:52:54 -0700 | From | "H. Peter Anvin" <> | Subject | Re: 2.6.{26.2,27-rc} oops on virtualbox |
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One thing that I think really needs to be considered is that the current PV stubs are (a) large, and (b) non-atomic.
In the case at hand we have:
c012fc69: 51 push %ecx c012fc6a: 52 push %edx c012fc6b: ff 15 40 b9 41 c0 call *0xc041b940 c012fc71: 5a pop %edx c012fc72: 59 pop %ecx
Ten bytes replacing a two-byte native sequence.
If this was done as a call to an out-of-line stub, it would be only five bytes, which would reduce native icache overhead from 400% to 150%, but perhaps more importantly, it would not be subject to returns inside the sequence itself (since the out-of-line stub would still exist.) As an optional bonus, at least on 32 bits the indirect call could be replaced with a direct call in the out-of-line stub.
-hpa
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