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

[Borislav Petkov]

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@xxxxxxxxxxxxxx>
> > 
> > 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@xxxxxxxxxxxxxxx>
> > Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> > ---
> >  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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