linux-kernel - Re: [PATCH 3/3] powerpc/pseries/mm: call H_BLOCK

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Message-Id: <87fu00olaf.fsf@linux.ibm.com>
Date:   Mon, 30 Jul 2018 19:52:48 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com
Subject: Re: [PATCH 3/3] powerpc/pseries/mm: call H_BLOCK_REMOVE

Michael Ellerman <mpe@...erman.id.au> writes:

> Hi Laurent,
>
> Just one comment below.
>
> Laurent Dufour <ldufour@...ux.vnet.ibm.com> writes:
>> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
>> index 96b8cd8a802d..41ed03245eb4 100644
>> --- a/arch/powerpc/platforms/pseries/lpar.c
>> +++ b/arch/powerpc/platforms/pseries/lpar.c
>> @@ -418,6 +418,73 @@ static void pSeries_lpar_hpte_invalidate(unsigned long slot, unsigned long vpn,
>>  	BUG_ON(lpar_rc != H_SUCCESS);
>>  }
>>  
>> +
>> +/*
>> + * As defined in the PAPR's section 14.5.4.1.8
>> + * The control mask doesn't include the returned reference and change bit from
>> + * the processed PTE.
>> + */
>> +#define HBLKR_AVPN		0x0100000000000000UL
>> +#define HBLKR_CTRL_MASK		0xf800000000000000UL
>> +#define HBLKR_CTRL_SUCCESS	0x8000000000000000UL
>> +#define HBLKR_CTRL_ERRNOTFOUND	0x8800000000000000UL
>> +#define HBLKR_CTRL_ERRBUSY	0xa000000000000000UL
>> +
>> +/**
>> + * H_BLOCK_REMOVE caller.
>> + * @idx should point to the latest @param entry set with a PTEX.
>> + * If PTE cannot be processed because another CPUs has already locked that
>> + * group, those entries are put back in @param starting at index 1.
>> + * If entries has to be retried and @retry_busy is set to true, these entries
>> + * are retried until success. If @retry_busy is set to false, the returned
>> + * is the number of entries yet to process.
>> + */
>> +static unsigned long call_block_remove(unsigned long idx, unsigned long *param,
>> +				       bool retry_busy)
>> +{
>> +	unsigned long i, rc, new_idx;
>> +	unsigned long retbuf[PLPAR_HCALL9_BUFSIZE];
>> +
>> +again:
>> +	new_idx = 0;
>> +	BUG_ON((idx < 2) || (idx > PLPAR_HCALL9_BUFSIZE));
>
> I count 1 ..
>
>> +	if (idx < PLPAR_HCALL9_BUFSIZE)
>> +		param[idx] = HBR_END;
>> +
>> +	rc = plpar_hcall9(H_BLOCK_REMOVE, retbuf,
>> +			  param[0], /* AVA */
>> +			  param[1],  param[2],  param[3],  param[4], /* TS0-7 */
>> +			  param[5],  param[6],  param[7],  param[8]);
>> +	if (rc == H_SUCCESS)
>> +		return 0;
>> +
>> +	BUG_ON(rc != H_PARTIAL);
>
> 2 ...
>
>> +	/* Check that the unprocessed entries were 'not found' or 'busy' */
>> +	for (i = 0; i < idx-1; i++) {
>> +		unsigned long ctrl = retbuf[i] & HBLKR_CTRL_MASK;
>> +
>> +		if (ctrl == HBLKR_CTRL_ERRBUSY) {
>> +			param[++new_idx] = param[i+1];
>> +			continue;
>> +		}
>> +
>> +		BUG_ON(ctrl != HBLKR_CTRL_SUCCESS
>> +		       && ctrl != HBLKR_CTRL_ERRNOTFOUND);
>
> 3 ...
>
> BUG_ON()s.
>
> I know the code in this file is already pretty liberal with the use of
> BUG_ON() but I'd prefer if we don't make it any worse.
>
> Given this is an optimisation it seems like we should be able to fall
> back to the existing implementation in the case of error (which will
> probably then BUG_ON() 😂)
>
> If there's some reason we can't then I guess I can live with it.

It would be nice to log the error in case we are not expecting the
error return. We recently did
https://marc.info/?i=20180629083904.29250-1-aneesh.kumar@linux.ibm.com

-aneesh