linux-kernel - [PATCH v2 0/2] powerpc/mm: Conditionally call H_BLOCK

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Date:   Mon, 16 Sep 2019 11:55:41 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        aneesh.kumar@...ux.ibm.com, npiggin@...il.com,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/2] powerpc/mm: Conditionally call H_BLOCK_REMOVE

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:

The PAPR document specifies the TLB Block Invalidate Characteristics which
tells for each couple segment base page size, actual page size, the size of
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.

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