Re: [Xen-devel] [PATCH] clflush instruction emulation

[Wei Huang <wei.huang2@xxxxxxx>]

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
>
>
>
>   


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel