On Fri, Aug 17, 2012 at 09:10:42AM +0900, OGAWA Hirofumi wrote:
> Marcelo Tosatti <mtosatti@xxxxxxxxxx> writes:
>
> > On Wed, Aug 15, 2012 at 11:05:57PM +0900, OGAWA Hirofumi wrote:
> >>
> >> If !CONFIG_KVM_GUEST, kvm_smp_prepare_boot_cpu() is not defined. So,
> >> kvm_register_clock("primary cpu clock") in kvm_smp_prepare_boot_cpu()
> >> is not called.
> >>
> >> The detail of problem is hv_clock percpu usage. hv_clock is percpu
> >> variable, but kvmclock_init() is called _before_ initializing percpu
> >> area, and doesn't update address after initialized percpu area.
> >>
> >> So, host kvm modify the memory area _before_ initializing percpu. This
> >> became the cause of strange memory corruption on guest OS.
> >>
> >>
> >> This fixes it by adding kvm_smp_prepare_boot_cpu(). [we might be
> >> better to kill the usage before percpu initialization.]
> >>
> >> Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
> >
> > The distinction between CONFIG_KVM_CLOCK and CONFIG_KVM_GUEST is
> > not so clear anymore, as this bug demonstrates.
> >
> > There is no point in having a separate config option, therefore i
> > propose to merge the two (see other reply) instead.
>
> Yes, it was an another option to fix this. As note, the wrong percpu
> usage (use it before initialization) is still true even if merged
> KVM_CLOCK.
Its fine, i believe, because there is a percpu area for the "boot
processor" (see __per_cpu_offset at arch/x86/kernel/setup_percpu.c)
before proper initialization.
Can you please confirm the proposed config merge fixes the problem
for you?
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
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