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xen-devel
Re: [Xen-devel] [PATCH] clflush instruction emulation
WBINVD is a bit heavy since it flushes all caches. I saw 1170 times of
CLFLUSH during FreeBSD booting. After guest boots, 0 was observed. 1170
is not huge though.
-Wei
Keir Fraser wrote:
On 15/04/2010 17:38, "Wei Huang" <wei.huang2@xxxxxxx> wrote:
I created a patch which enables clflush emulation. I have verified that
this patch solves FreeBSD issue. This patch returns immediately without
doing anything. Note that we don't have to intercept clflush in SVM. So
the only time we have page_fault for clflush instruction is when guest
VM flushes MMIO space. In this case, do we need to send this command
over to QEMU? I didn't do it in this patch anyway.
I don't think we need to anything since all guest reads/writes to the mmio
space will get intercepted to qemu, and hence qemu's view of the space is
coherent with the guest with no need for special handling of CLFLUSH.
Still the emulator should call out and let the caller decide what to do. We
could safely turn CLFLUSH into WBINVD (i.e., call the existing wbinvd hook).
Do you know if these CLFLUSH emulations happen often or only very rarely?
That might help us decide how smart we need to be about emulating CLFLUSH
(i.e., add a hook specifically for clflush, separately from wbinvd).
-- Keir
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