From: Michael Ellerman <mpe@ellerman•id.au>
To: Ian Munsie <imunsie@au1•ibm.com>
Cc: Matt Ochs <mrochs@us•ibm.com>,
linuxppc-dev <linuxppc-dev@ozlabs•org>, mikey <mikey@neuling•org>,
linux-kernel <linux-kernel@vger•kernel.org>,
Ian Munsie <imunsie@au1•ibm.com>
Subject: Re: cxl: Add alternate MMIO error handling
Date: Thu, 20 Aug 2015 09:14:16 +1000 (AEST) [thread overview]
Message-ID: <20150819231416.858091409B7@ozlabs.org> (raw)
In-Reply-To: <1437633836-5051-1-git-send-email-imunsie@au.ibm.com>
On Thu, 2015-23-07 at 06:43:56 UTC, Ian Munsie wrote:
> From: Ian Munsie <imunsie@au1•ibm.com>
>
> userspace programs using cxl currently have to use two strategies for
> dealing with MMIO errors simultaneously. They have to check every read
> for a return of all Fs in case the adapter has gone away and the kernel
> has not yet noticed, and they have to deal with SIGBUS in case the
> kernel has already noticed, invalidated the mapping and marked the
> context as failed.
>
> In order to simplify things, this patch adds an alternative approach
> where the kernel will return a page filled with Fs instead of delivering
> a SIGBUS. This allows userspace to only need to deal with one of these
> two error paths, and is intended for use in libraries that use cxl
> transparently and may not be able to safely install a signal handler.
>
> This approach will only work if certain constraints are met. Namely, if
> the application is both reading and writing to an address in the problem
> state area it cannot assume that a non-FF read is OK, as it may just be
> reading out a value it has previously written. Further - since only one
> page is used per context a write to a given offset would be visible when
> reading the same offset from a different page in the mapping (this only
> applies within a single context, not between contexts).
>
> An application could deal with this by e.g. making sure it also reads
> from a read-only offset after any reads to a read/write offset.
>
> Due to these constraints, this functionality must be explicitly
> requested by userspace when starting the context by passing in the
> CXL_START_WORK_ERR_FF flag.
>
> Signed-off-by: Ian Munsie <imunsie@au1•ibm.com>
> Acked-by: Michael Neuling <mikey@neuling•org>
Applied to powerpc next, thanks.
https://git.kernel.org/powerpc/c/d9232a3da8683cd9c985
cheers
prev parent reply other threads:[~2015-08-19 23:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-23 6:43 [PATCH] cxl: Add alternate MMIO error handling Ian Munsie
2015-08-07 3:19 ` Michael Neuling
2015-08-19 23:14 ` Michael Ellerman [this message]
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