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Subject: Re: [PATCH v2 0/2] powerpc/mm: Conditionally call H_BLOCK_REMOVE
To:     Laurent Dufour <ldufour@linux.ibm.com>, mpe@ellerman.id.au,
        benh@kernel.crashing.org, paulus@samba.org, npiggin@gmail.com,
        linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20190916095543.17496-1-ldufour@linux.ibm.com>
From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Message-ID: <1ba1bfc7-66c2-5298-2ef2-4117cb72ee13@linux.ibm.com>
Date:   Tue, 17 Sep 2019 21:42:55 +0530
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On 9/16/19 3:25 PM, Laurent Dufour wrote:
> 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
> 

you can use

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

for the series.

-aneesh