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Date: Wed, 14 Apr 2021 14:01:00 +0530
From: Mahesh J Salgaonkar <mahesh@linux.ibm.com>
To: "Oliver O'Halloran" <oohall@gmail.com>
Subject: Re: [PATCH v2] powerpc/eeh: Fix EEH handling for hugepages in
 ioremap space.
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Cc: linuxppc-dev <linuxppc-dev@ozlabs.org>, stable <stable@vger.kernel.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
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On 2021-04-13 10:53:39 Tue, Oliver O'Halloran wrote:
> On Mon, Apr 12, 2021 at 5:52 PM Mahesh Salgaonkar <mahesh@linux.ibm.com> wrote:
> >
> > During the EEH MMIO error checking, the current implementation fails to map
> > the (virtual) MMIO address back to the pci device on radix with hugepage
> > mappings for I/O. This results into failure to dispatch EEH event with no
> > recovery even when EEH capability has been enabled on the device.
> >
> > eeh_check_failure(token)                # token = virtual MMIO address
> >   addr = eeh_token_to_phys(token);
> >   edev = eeh_addr_cache_get_dev(addr);
> >   if (!edev)
> >         return 0;
> >   eeh_dev_check_failure(edev);  <= Dispatch the EEH event
> >
> > In case of hugepage mappings, eeh_token_to_phys() has a bug in virt -> phys
> > translation that results in wrong physical address, which is then passed to
> > eeh_addr_cache_get_dev() to match it against cached pci I/O address ranges
> > to get to a PCI device. Hence, it fails to find a match and the EEH event
> > never gets dispatched leaving the device in failed state.
> >
> > The commit 33439620680be ("powerpc/eeh: Handle hugepages in ioremap space")
> > introduced following logic to translate virt to phys for hugepage mappings:
> >
> > eeh_token_to_phys():
> > +       pa = pte_pfn(*ptep);
> > +
> > +       /* On radix we can do hugepage mappings for io, so handle that */
> > +       if (hugepage_shift) {
> > +               pa <<= hugepage_shift;                  <= This is wrong
> > +               pa |= token & ((1ul << hugepage_shift) - 1);
> > +       }
> 
> I think I vaguely remember thinking "is this right?" at the time.
> Apparently not!
> 
> Reviewed-by: Oliver O'Halloran <oohall@gmail.com>
> 

Thanks for the review.

> 
> It would probably be a good idea to add a debugfs interface to help
> with testing the address translation. Maybe something like:
> 
> echo <mmio addr> > /sys/kernel/debug/powerpc/eeh_addr_check
> 
> Then in the kernel:
> 
> struct resource *r = lookup_resource(mmio_addr);
> void *virt = ioremap_resource(r);
> ret = eeh_check_failure(virt);
> iounmap(virt)
> 
> return ret;
> 
> A little tedious, but then you can write a selftest :)

Sure, will give a try.

Thanks,
-Mahesh.

-- 
Mahesh J Salgaonkar