Re: [Xen-merge] write_cr{0,4}

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

Writes to cr0 already are emulated -- the TS bit is virtualised and all 
other modified bits are ignored. We could also emulate (ignore) writes 
to cr4, if that avoids xen-specific changes in the guest. The change to 
do this is utterly trivial. Reads of cr4 are already emulated.
 -- Keir

On 23 Dec 2005, at 11:09, Jan Beulich wrote:

> While merging i386's system.h I intended to remove those operations 
> that
> the hypervisor doesn't support, namely writing to cr0 or cr4. However,
> even code in xen-specific files makes use of them, so far I found
>
> - write_cr0 in no_387() in include/asm-i386/bugs.h
> - write_cr4 in disable_tsc() in arch/i386/kernel/process-xen.c
> - write_cr0 in set_cx86_memwb() in arch/i386/kernel/cpu/cyrix.c
>
> I'll therefore have to (temporarily) re-add these functions, but will
> make them BUG() instead of attempting the writes, with the expectation
> that the offending uses get fixed in some way. Otherwise, proper 
> support
> will need to be added to the hypervisor.
>
> Jan
>
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