linux-kernel - Re: [PATCH 2/3] powperc/mm: read TLB Block Invalidate Characteristics

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Message-ID: <97bafb53-6ae9-1d42-1816-ef81b845b80c@linux.ibm.com>
Date:   Fri, 13 Sep 2019 07:30:42 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] powperc/mm: read TLB Block Invalidate Characteristics

On 9/13/19 12:56 AM, Laurent Dufour wrote:
> Le 12/09/2019 à 16:44, Aneesh Kumar K.V a écrit :
>> Laurent Dufour <ldufour@...ux.ibm.com> writes:

>>> +
>>> +    idx = 2;
>>> +    while (idx < len) {
>>> +        unsigned int block_size = local_buffer[idx++];
>>> +        unsigned int npsize;
>>> +
>>> +        if (!block_size)
>>> +            break;
>>> +
>>> +        block_size = 1 << block_size;
>>> +        if (block_size != 8)
>>> +            /* We only support 8 bytes size TLB invalidate buffer */
>>> +            pr_warn("Unsupported H_BLOCK_REMOVE block size : %d\n",
>>> +                block_size);
>>
>> Should we skip setting block size if we find block_size != 8? Also can
>> we avoid doing that pr_warn in loop and only warn if we don't find
>> block_size 8 in the invalidate characteristics array?
> 
> My idea here is to fully read and process the data returned by the 
> hcall, and to put the limitation to 8 when checking before calling 
> H_BLOCK_REMOVE.
> The warning is there because I want it to be displayed once at boot.
> 


Can we have two block size reported for the same base page size/actual 
page size combination? If so we will overwrite the hblk[actual_psize] ?

>>
>>> +
>>> +        for (npsize = local_buffer[idx++];  npsize > 0; npsize--)
>>> +            check_lp_set_hblk((unsigned int) local_buffer[idx++],
>>> +                      block_size);
>>> +    }
>>> +
>>> +    for (bpsize = 0; bpsize < MMU_PAGE_COUNT; bpsize++)
>>> +        for (idx = 0; idx < MMU_PAGE_COUNT; idx++)
>>> +            if (mmu_psize_defs[bpsize].hblk[idx])
>>> +                pr_info("H_BLOCK_REMOVE supports base psize:%d 
>>> psize:%d block size:%d",
>>> +                    bpsize, idx,
>>> +                    mmu_psize_defs[bpsize].hblk[idx]);
>>> +
>>> +    return 0;
>>> +}
>>> +machine_arch_initcall(pseries, read_tlbbi_characteristics);
>>> +
>>>   /*
>>>    * Take a spinlock around flushes to avoid bouncing the hypervisor 
>>> tlbie
>>>    * lock.

-aneesh