Re: [PATCH 1/2] kvm: Fix x86 emulator writeback

[Avi Kivity <avi@qumranet.com>]

Avi Kivity wrote:
> Luca Tettamanti wrote:
> > When the old value and new one are the same the emulator skips the
> > write; this is undesiderable when the destination is a MMIO area and the
> > write shall be performed regardless of the previous value. This
> > optimization breaks e.g. a Linux guest APIC compiled without
> > X86_GOOD_APIC.
> >
> > Remove the check and always perform the writeback stage in the
> > emulation.
> >
> >   
>
> Unfortunately, this kills Windows XP (first run with a guest crash, 
> second with a host oops), so I reverted it.  I'd guess some operation  
> which doesn't need writeback ends up in the modified code.  
> Previously, the check caused it to skip writeback, but now it writes 
> back random memory, causing a crash.

There are comments around like

>     /* Disable writeback. */
>     dst.orig_val = dst.val;

Best option is probably to add an explicit disable_writeback flag and 
set it there.

--
error compiling committee.c: too many arguments to function

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