Hi Laurent,
Thanks for fixing this, just a few comments.
Laurent Dufour <ldufour@xxxxxxxxxxxxx> writes:
> Since the commit ba2dd8a26baa ("powerpc/pseries/mm: call H_BLOCK_REMOVE"),
> the call to H_BLOCK_REMOVE is always done if the feature is exhibited.
>
> However, the hypervisor may not support all the block size for the hcall
> H_BLOCK_REMOVE depending on the segment base page size and actual page
> size.
>
> When unsupported block size is used, the hcall H_BLOCK_REMOVE is returning
> H_PARAM, which is triggering a BUG_ON check leading to a panic like this:
Missing panic :)
Also can you put that detail in the 2nd commit, so that it's obvious
that it is a fix for an oops.
> The PAPR document specifies the TLB Block Invalidate Characteristics which
Can you give a section/page number for the PAPR reference.
> tells for each couple segment base page size, actual page size, the size of
^
"pair of" is better than "couple" I think
> the block the hcall H_BLOCK_REMOVE is supporting.
>
> Supporting various block sizes doesn't seem needed at that time since all
> systems I was able to play with was supporting an 8 addresses block size,
> which is the maximum through the hcall, or none at all. Supporting various
> size would complexify the algorithm in call_block_remove() so unless this
> is required, this is not done.
>
> In the case of block size different from 8, a warning message is displayed
> at boot time and that block size will be ignored checking for the
> H_BLOCK_REMOVE support.
>
> Due to the minimal amount of hardware showing a limited set of
> H_BLOCK_REMOVE supported page size, I don't think there is a need to push
> this series to the stable mailing list.
But the hardware that is exhibiting it, by crashing and not booting, is
mostly (all?) older hardware. So I think we probably should send it back
to stable, otherwise those machines may never get an updated kernel.
Can you add Fixes: tags to the commits, they should point at the commit
that added H_BLOCK_REMOVE support.
cheers
> The first patch is reading the characteristic through the hcall
> ibm,get-system-parameter and record the supported block size for each page
> size. The second patch is changing the check used to detect the
> H_BLOCK_REMOVE availability to take care of the base page size and page
> size couple.
>
> Changes since V1:
>
> - Remove penc initialisation, this is already done in
> mmu_psize_set_default_penc()
> - Add details on the TLB Block Invalidate Characteristics's buffer format
> - Introduce #define instead of using direct numerical values
> - Function reading the characteristics is now directly called from
> pSeries_setup_arch()
> - The characteristics are now stored in a dedciated table static to lpar.c
>
> Laurent Dufour (2):
> powperc/mm: read TLB Block Invalidate Characteristics
> powerpc/mm: call H_BLOCK_REMOVE when supported
>
> .../include/asm/book3s/64/tlbflush-hash.h | 1 +
> arch/powerpc/platforms/pseries/lpar.c | 173 +++++++++++++++++-
> arch/powerpc/platforms/pseries/setup.c | 1 +
> 3 files changed, 173 insertions(+), 2 deletions(-)
>
> --
> 2.23.0
