From: arnd@arndb•de (Arnd Bergmann)
To: linux-arm-kernel@lists•infradead.org
Subject: Physical memory start contraints in the Linux kernel (Was: Re: Xen osstest on Calxeda midway progress (Was: Re: [Xen-devel] [xen-unstable test] 21486: tolerable FAIL - PUSHED))
Date: Wed, 13 Nov 2013 20:42:32 +0100 [thread overview]
Message-ID: <201311132042.32725.arnd@arndb.de> (raw)
In-Reply-To: <alpine.DEB.2.02.1311131417030.4714@kaball.uk.xensource.com>
On Wednesday 13 November 2013, Stefano Stabellini wrote:
>
> -#define xchg_xen_ulong(ptr, val) atomic64_xchg(container_of((ptr), \
> +#ifdef CONFIG_GENERIC_ATOMIC64
> +/* if CONFIG_GENERIC_ATOMIC64 is defined we cannot use the generic
> + * atomic64_xchg function because it is implemented using spin locks.
> + * Here we need proper atomic instructions to read and write memory
> + * shared with the hypervisor.
> + */
> +static inline u64 xen_atomic64_xchg(atomic64_t *ptr, u64 new)
> +{
> + u64 result;
> + unsigned long tmp;
> +
> + smp_mb();
> +
> + __asm__ __volatile__("@ xen_atomic64_xchg\n"
> +"1: ldrexd %0, %H0, [%3]\n"
> +" strexd %1, %4, %H4, [%3]\n"
> +" teq %1, #0\n"
> +" bne 1b"
> + : "=&r" (result), "=&r" (tmp), "+Qo" (ptr->counter)
> + : "r" (&ptr->counter), "r" (new)
> + : "cc");
> +
> + smp_mb();
> +
> + return result;
> +}
> +#else
> +#define xen_atomic64_xchg atomic64_xchg
> +#endif
I would prefer not duplicating this code. Maybe we can instead change
the ARM code to always provide this function under the name of
armv7_atomic64_xchg() and conditionally defining atomic64_xchg
to use it. Let's see if Russell has an opinion on this, or perhaps
a better solution.
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 62ccf54..d668c3c 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -33,6 +33,14 @@
>
> #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
>
> +/* This is required because cmpxchg only support 32-bits operands on
> + * ARMv6, so if CONFIG_CPU_V6 is defined the cmpxchg implemention will
> + * be limited to 32-bits operands.
> + * However we know for sure that if Linux is running on Xen, the
> + * platform is >= ARMv7, so here we can safely undef CONFIG_CPU_V6.
> + */
> +#undef CONFIG_CPU_V6
> +
> #include <linux/module.h>
> #include <linux/sched.h>
> #include <linux/mm.h>
>
Same here: I'd prefer making this more explicit by changing the cmpxchg
implementation: we could split out the 16-bit cmpxchg case into a separate
function with "armv7" in the name and only call that from the main
cmpxchg() implementations when building an armv7-only kernel, but still
let you call it from Xen code that is known to run only on armv7.
Arnd
next prev parent reply other threads:[~2013-11-13 19:42 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <osstest-21486-mainreport@xen.org>
[not found] ` <1383731526.26213.25.camel@kazak.uk.xensource.com>
[not found] ` <alpine.DEB.2.02.1311061111580.26077@kaball.uk.xensource.com>
[not found] ` <1383736784.26213.72.camel@kazak.uk.xensource.com>
[not found] ` <alpine.DEB.2.02.1311061938080.26077@kaball.uk.xensource.com>
[not found] ` <1383822868.26213.181.camel@kazak.uk.xensource.com>
[not found] ` <alpine.DEB.2.02.1311111825090.26077@kaball.uk.xensource.com>
[not found] ` <1384250005.1883.35.camel@kazak.uk.xensource.com>
2013-11-12 12:25 ` Physical memory start contraints in the Linux kernel (Was: Re: Xen osstest on Calxeda midway progress (Was: Re: [Xen-devel] [xen-unstable test] 21486: tolerable FAIL - PUSHED)) Stefano Stabellini
2013-11-12 13:20 ` Russell King - ARM Linux
2013-11-12 14:38 ` Ian Campbell
2013-11-12 14:44 ` Russell King - ARM Linux
2013-11-12 14:52 ` Ian Campbell
2013-11-12 15:24 ` Michal Simek
2013-11-12 15:39 ` Russell King - ARM Linux
2013-11-12 15:40 ` Michal Simek
2013-11-12 13:37 ` Arnd Bergmann
2013-11-12 14:35 ` Julien Grall
2013-11-12 14:40 ` Ian Campbell
2013-11-12 18:39 ` Arnd Bergmann
2013-11-12 18:47 ` Stefano Stabellini
2013-11-12 20:08 ` Arnd Bergmann
2013-11-13 10:50 ` Ian Campbell
2013-11-13 17:33 ` Stefano Stabellini
2013-11-13 19:42 ` Arnd Bergmann [this message]
2013-11-14 15:24 ` Stefano Stabellini
2013-11-12 14:41 ` Russell King - ARM Linux
2013-11-12 14:52 ` [Xen-devel] Physical memory start contraints in the Linux kernel (Was: Re: Xen osstest on Calxeda midway progress (Was: " Julien Grall
2013-11-12 14:57 ` Ian Campbell
2013-11-12 15:24 ` Julien Grall
2013-11-12 15:32 ` Ian Campbell
2013-11-13 12:57 ` Julien Grall
2013-11-12 15:00 ` Physical memory start contraints in the Linux kernel (Was: Re: Xen osstest on Calxeda midway progress (Was: Re: [Xen-devel] " Stefano Stabellini
2013-11-12 15:16 ` Russell King - ARM Linux
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