Re: [PATCH 05/10] MCE: Mask out address mask bits below address granuality

Borislav Petkov
2011-06-10T09:46:55Z

On Fri, Jun 10, 2011 at 04:07:13AM -0400, Hidetoshi Seto wrote:
> (2011/06/10 6:33), Luck, Tony wrote:
> > From: Andi Kleen <andi@firstfloor.org>
> >
> > SER enabled systems report the address granuality for each
> > reported address in a machine check. But the bits below
> > the granuality are undefined. Mask them out before
> > logging the machine check.
> >
> > Signed-off-by: Andi Kleen <ak@linux.intel.com>
> > Signed-off-by: Tony Luck <tony.luck@intel.com>
> > ---
> > arch/x86/kernel/cpu/mcheck/mce.c | 12 +++++++++++-
> > 1 files changed, 11 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> > index 0349e87..ffc8d11 100644
> > --- a/arch/x86/kernel/cpu/mcheck/mce.c
> > +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> > @@ -539,8 +539,18 @@ static void mce_read_aux(struct mce *m, int i)
> > {
> > if (m->status & MCI_STATUS_MISCV)
> > m->misc = mce_rdmsrl(MSR_IA32_MCx_MISC(i));
> > - if (m->status & MCI_STATUS_ADDRV)
> > + if (m->status & MCI_STATUS_ADDRV) {
> > m->addr = mce_rdmsrl(MSR_IA32_MCx_ADDR(i));
> > +
> > + /*
> > + * Mask the reported address by the reported granuality.
> > + */
> > + if (mce_ser && (m->status & MCI_STATUS_MISCV)) {
> > + u8 shift = m->misc & 0x1f;
> > + m->addr >>= shift;
> > + m->addr <<= shift;
> > + }
> > + }
> > }
> >
> > DEFINE_PER_CPU(unsigned, mce_poll_count);
>
> Why do you have to mask it out in kernel, why not in user/logger?
>
> One possible story is:
> "... the brand-new Xeon XXXX has new MCx_***_VALID bit in ****
> register, if it is set the lower bits of MCx_ADDR indicates
> ****, otherwise the bits are undefined ..."
>
> So I think that kernel should convey the raw value from hardware to
> userland. Even if it contains some noise on it, user can determine
> whether it is useful or not. And more, since this is an error record,
> there will be no second chance to retrieve the data afterward.

I think they need the correct address for the poisoning later:

if (severity == MCE_AO_SEVERITY && mce_usable_address(&m))
mce_ring_add(m.addr >> PAGE_SHIFT);

Tony?

--
Regards/Gruss,
Boris.

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