[Qemu-devel] Re: [PATCH uq/master 2/2] MCE, unpoison memory address across reboot

[Huang Ying]

On Fri, 2011-01-14 at 16:38 +0800, Jan Kiszka wrote:
> Am 14.01.2011 02:51, Huang Ying wrote:
> > On Thu, 2011-01-13 at 17:01 +0800, Jan Kiszka wrote:
> >> Am 13.01.2011 09:34, Huang Ying wrote:
[snip]
> >>> +
> >>> +void kvm_unpoison_all(void *param)
> >>
> >> Minor nit: This can be static now.
> > 
> > In uq/master, it can be make static.  But in kvm/master, kvm_arch_init
> > is not compiled because of conditional compiling, so we will get warning
> > and error for unused symbol.  Should we consider kvm/master in this
> > patch?
> 
> qemu-kvm is very close to switching to upstream kvm_*init. As long as it
> requires this service in its own modules, it will have to patch this
> detail. It does this for other functions already.

OK.  I will change this.

[snip]
> >> As indicated, I'm sitting on lots of fixes and refactorings of the MCE
> >> user space code. How do you test your patches? Any suggestions how to do
> >> this efficiently would be warmly welcome.
> > 
> > We use a self-made test script to test.  Repository is at:
> > 
> > git://git.kernel.org/pub/scm/utils/cpu/mce/mce-test.git
> > 
> > The kvm test script is in kvm sub-directory.
> > 
> > The qemu patch attached is need by the test script.
> > 
> 
> Yeah, I already found this yesterday and started reading. I was just
> searching for p2v in qemu, but now it's clear where it comes from. Will
> have a look (if you want to preview my changes:
> git://git.kiszka.org/qemu-kvm.git queues/kvm-upstream).
> 
> I was almost about to use MADV_HWPOISON instead of the injection module.
> Is there a way to recover the fake corruption afterward? I think that
> would allow to move some of the test logic into qemu and avoid p2v which
> - IIRC - was disliked upstream.

I don't know how to fully recover from  MADV_HWPOISON.  You can recover
the virtual address space via qemu_ram_remap() introduced in 1/2 of this
patchset.  But you will lose one or several physical pages for each
testing.  I think that may be not a big issue for a testing machine.

Ccing Andi and Fengguang, they know more than me about MADV_HWPOISON.

> Also, is there a way to simulate corrected errors (BUS_MCEERR_AO)?

BUS_MCEERR_AO is recoverable uncorrected error instead of corrected
error.

The test script is for BUS_MCEERR_AO and BUS_MCEERR_AR.  To see the
effect of pure BUS_MCEERR_AO, just remove the memory accessing loop
(memset) in tools/simple_process/simple_process.c.

Best Regards,
Huang Ying