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From: Keith Busch <>
To: Sagi Grimberg <>
	Eduard Hasenleithner <>
Subject: Re: [RFC PATCH] Workaround for discard on non-conformant nvme devices
Date: Thu, 7 Nov 2019 03:23:39 +0900
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, Nov 06, 2019 at 08:52:20AM -0800, Sagi Grimberg wrote:
> > As documented in
> > there are lots of Linux nvme users which get IO-MMU related errors when
> > performing discard on nvme. So far analysis suggests that the errors are
> > caused by non-conformat nvme devices which are reading beyond the end of
> > the buffer containing the segments to be discarded.
> > 
> > Until now two different variants of this behavior have been observed:
> > The controller found on an Intel 660p always reads a multiple of 512
> > bytes. If the last chunk exceeds a page it continues with the subsequent
> > page. For a Corsair MP510 the situation is even worse: The controller
> > always reads a full page (4096) bytes. Then when the address is not
> > aligned to 4096 it will continue reading at the address given in PRP2
> > (which is most of the time 0).
> > 
> > This patch makes the nvme_setup_discard function always request a
> > multiple of a page size (4096) from the kernel for storing the segment
> > array. Since this makes the buffer always page-aligned the device
> > reading beyond end of a page is avoided.
> This needs to come with a quirk for it.

Yeah, and have the broken ones to use the ctrl->discard_page so that you
don't need to worry about the alignment of the address kmalloc returns.

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Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-04 21:47 Eduard Hasenleithner
2019-11-06 16:52 ` Sagi Grimberg
2019-11-06 18:23   ` Keith Busch [this message]
2019-11-06 20:22     ` Eduard Hasenleithner
2019-11-06 20:43       ` Keith Busch
2019-11-06 21:10         ` Eduard Hasenleithner
2019-11-06 21:34           ` Keith Busch

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