Re: [PATCH] powerpc/eeh: Handle hugepages in ioremap space

On 10-Jul-2019, at 8:35 PM, Oliver O'Halloran [off-list ref] wrote:

In commit 4a7b06c157a2 ("powerpc/eeh: Handle hugepages in ioremap
space") support for using hugepages in the vmalloc and ioremap areas was
enabled for radix. Unfortunately this broke EEH MMIO error checking.

Detection works by inserting a hook which checks the results of the
ioreadXX() set of functions.  When a read returns a 0xFFs response we
need to check for an error which we do by mapping the (virtual) MMIO
address back to a physical address, then mapping physical address to a
PCI device via an interval tree.

When translating virt -> phys we currently assume the ioremap space is
only populated by PAGE_SIZE mappings. If a hugepage mapping is found we
emit a WARN_ON(), but otherwise handles the check as though a normal
page was found. In pathalogical cases such as copying a buffer
containing a lot of 0xFFs from BAR memory this can result in the system
not booting because it's too busy printing WARN_ON()s.

There's no real reason to assume huge pages can't be present and we're
prefectly capable of handling them, so do that.

Cc: Nicholas Piggin <npiggin@gmail.com>
Fixes: 4a7b06c157a2 ("powerpc/eeh: Handle hugepages in ioremap space")
Reported-by: Sachin Sant <redacted>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

Tested-by: Sachin Sant <redacted>

Thanks
-Sachin