From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH] arm64: make bitops 32-bit tolerant
Date: Mon, 28 Apr 2014 09:45:56 +0100 [thread overview]
Message-ID: <20140428084556.GA12090@arm.com> (raw)
In-Reply-To: <1398590477-15375-1-git-send-email-murzin.v@gmail.com>
On Sun, Apr 27, 2014 at 10:21:17AM +0100, Vladimir Murzin wrote:
> Xen assumes that bit operations are able to operate on 32-bit size and
> alignment [1]. For arm64 bitops are based on atomic exclusive load/store
> instructions to guarantee that changes are made atomically. However, these
> instructions require that address to be aligned to the data size. Because, by
> default, bitops operates on 64-bit size it implies that address should be
> aligned appropriately. All these lead to breakage of Xen assumption for bitops
> properties.
>
> This patch turns bitops to operate on 32-bit size/alignment.
Please stop sending this patch. I have _absolutely_ _no_ intention of
butchering our bitops in this way, and I don't think the Xen guys require
changing the core bitops like this either (certainly, Ian's last reply to
you suggested you should be doing this another way).
NAK.
Will
> [1] http://www.gossamer-threads.com/lists/xen/devel/325613
>
> Cc: catalin.marinas at arm.com
> Cc: will.deacon at arm.com
> Cc: david.vrabel at citrix.com
> Cc: Ian.Campbell at citrix.com
>
> Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
> ---
> With this patch applied I was able to boot both Dom0 and DomU.
>
> @Pranav: Could I have your Tested-by on this patch?
>
> arch/arm64/lib/bitops.S | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/lib/bitops.S b/arch/arm64/lib/bitops.S
> index 7dac371..a6acfff 100644
> --- a/arch/arm64/lib/bitops.S
> +++ b/arch/arm64/lib/bitops.S
> @@ -26,14 +26,14 @@
> */
> .macro bitop, name, instr
> ENTRY( \name )
> - and w3, w0, #63 // Get bit offset
> + and w3, w0, #31 // Get bit offset
> eor w0, w0, w3 // Clear low bits
> mov x2, #1
> add x1, x1, x0, lsr #3 // Get word offset
> lsl x3, x2, x3 // Create mask
> -1: ldxr x2, [x1]
> - \instr x2, x2, x3
> - stxr w0, x2, [x1]
> +1: ldxr w2, [x1]
> + \instr w2, w2, w3
> + stxr w0, w2, [x1]
> cbnz w0, 1b
> ret
> ENDPROC(\name )
> @@ -41,15 +41,15 @@ ENDPROC(\name )
>
> .macro testop, name, instr
> ENTRY( \name )
> - and w3, w0, #63 // Get bit offset
> + and w3, w0, #31 // Get bit offset
> eor w0, w0, w3 // Clear low bits
> mov x2, #1
> add x1, x1, x0, lsr #3 // Get word offset
> lsl x4, x2, x3 // Create mask
> -1: ldxr x2, [x1]
> +1: ldxr w2, [x1]
> lsr x0, x2, x3 // Save old value of bit
> - \instr x2, x2, x4 // toggle bit
> - stlxr w5, x2, [x1]
> + \instr w2, w2, w4 // toggle bit
> + stlxr w5, w2, [x1]
> cbnz w5, 1b
> dmb ish
> and x0, x0, #1
> --
> 1.8.3.2
>
>
next prev parent reply other threads:[~2014-04-28 8:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-27 9:21 [RFC PATCH] arm64: make bitops 32-bit tolerant Vladimir Murzin
2014-04-28 8:45 ` Will Deacon
2014-04-28 8:45 ` Will Deacon [this message]
2014-04-28 9:15 ` Vladimir Murzin
2014-04-28 9:15 ` Vladimir Murzin
2014-04-27 9:21 Vladimir Murzin
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