linux-kernel - Re: CXL: Fix PSL error due to duplicate segment table entries

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Message-Id: <20141027064100.D12B514007D@ozlabs.org>
Date:	Mon, 27 Oct 2014 17:41:00 +1100 (AEDT)
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Ian Munsie <imunsie@....ibm.com>, mpe <mpe@...erman.id.au>
Cc:	cbe-oss-dev <cbe-oss-dev@...ts.ozlabs.org>,
	mikey <mikey@...ling.org>, arnd <arnd@...db.de>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	greg <greg@...ah.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...abs.org>, anton <anton@...ba.org>,
	imunsie <imunsie@....ibm.com>, jk <jk@...abs.org>
Subject: Re: CXL: Fix PSL error due to duplicate segment table entries

On Mon, 2014-27-10 at 04:24:35 UTC, Ian Munsie wrote:
> From: Ian Munsie <imunsie@....ibm.com>
> 
> In certain circumstances the PSL can send an interrupt for a segment

Define PSL before using it please.

> miss that the kernel has already handled. This can happen if multiple
> translations for the same segment are queued in the PSL before the
> kernel has restarted the first translation.
> 
> The CXL driver did not expect this situation and did not check if a

does not and does not, you haven't patched it yet.

> segment had already been handled. This could cause a duplicate segment
> table entry which in turn caused a PSL error taking down the card.
> 
> This patch fixes the issue by checking for existing entries in the
> segment table that match the segment it is trying to insert to avoid
> inserting duplicate entries.
> 
> Some of the code has been refactored to simplify it - the segment table
> hash has been moved from cxl_load_segment to find_free_sste where it is

Any reason that's not a separate patch?

> used and we have disabled the secondary hash in the segment table to
> reduce the number of entries that need to be tested from 16 to 8. Due to
> the large segment sizes we use it is extremely unlikely that the
> secondary hash would ever have been used in practice, so this should not
> have any negative impacts and may even improve performance.

Any reason that's not a separate patch?

> copro_calculate_slb will now mask the ESID by the correct mask for 1T vs

Didn't, but will after this patch?

> 256M segments. This has no effect by itself as the extra bits were
> ignored, but it makes debugging the segment table entries easier and
> means that we can directly compare the ESID values for duplicates
> without needing to worry about masking in the comparison.

Separate patch?

cheers
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