Re: [Xen-devel] [PATCH 02/24] xen/arm: hypercalls

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jul 26, 2012 at 04:33:44PM +0100, Stefano Stabellini wrote:
> Use r12 to pass the hypercall number to the hypervisor.
> 
> We need a register to pass the hypercall number because we might not
> know it at compile time and HVC only takes an immediate argument.
> 
> Among the available registers r12 seems to be the best choice because it
> is defined as "intra-procedure call scratch register".
> 
> Use the ISS to pass an hypervisor specific tag.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  arch/arm/include/asm/xen/hypercall.h |   50 ++++++++++++++++++++++++++
>  arch/arm/xen/Makefile                |    2 +-
>  arch/arm/xen/hypercall.S             |   65 ++++++++++++++++++++++++++++++++++
>  3 files changed, 116 insertions(+), 1 deletions(-)
>  create mode 100644 arch/arm/include/asm/xen/hypercall.h
>  create mode 100644 arch/arm/xen/hypercall.S
> 
> diff --git a/arch/arm/include/asm/xen/hypercall.h b/arch/arm/include/asm/xen/hypercall.h
> new file mode 100644
> index 0000000..4ac0624
> --- /dev/null
> +++ b/arch/arm/include/asm/xen/hypercall.h
> @@ -0,0 +1,50 @@
> +/******************************************************************************
> + * hypercall.h
> + *
> + * Linux-specific hypervisor handling.
> + *
> + * Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Citrix, 2012
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version 2
> + * as published by the Free Software Foundation; or, when distributed
> + * separately from the Linux kernel or incorporated into other
> + * software packages, subject to the following license:
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this source file (the "Software"), to deal in the Software without
> + * restriction, including without limitation the rights to use, copy, modify,
> + * merge, publish, distribute, sublicense, and/or sell copies of the Software,
> + * and to permit persons to whom the Software is furnished to do so, subject to
> + * the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> + * IN THE SOFTWARE.
> + */
> +
> +#ifndef _ASM_ARM_XEN_HYPERCALL_H
> +#define _ASM_ARM_XEN_HYPERCALL_H
> +
> +#include <xen/interface/xen.h>
> +
> +long privcmd_call(unsigned call, unsigned long a1,
> +		unsigned long a2, unsigned long a3,
> +		unsigned long a4, unsigned long a5);
> +int HYPERVISOR_xen_version(int cmd, void *arg);
> +int HYPERVISOR_console_io(int cmd, int count, char *str);
> +int HYPERVISOR_grant_table_op(unsigned int cmd, void *uop, unsigned int count);
> +int HYPERVISOR_sched_op(int cmd, void *arg);
> +int HYPERVISOR_event_channel_op(int cmd, void *arg);
> +unsigned long HYPERVISOR_hvm_op(int op, void *arg);
> +int HYPERVISOR_memory_op(unsigned int cmd, void *arg);
> +int HYPERVISOR_physdev_op(int cmd, void *arg);
> +
> +#endif /* _ASM_ARM_XEN_HYPERCALL_H */
> diff --git a/arch/arm/xen/Makefile b/arch/arm/xen/Makefile
> index 0bad594..b9d6acc 100644
> --- a/arch/arm/xen/Makefile
> +++ b/arch/arm/xen/Makefile
> @@ -1 +1 @@
> -obj-y		:= enlighten.o
> +obj-y		:= enlighten.o hypercall.o
> diff --git a/arch/arm/xen/hypercall.S b/arch/arm/xen/hypercall.S
> new file mode 100644
> index 0000000..038cc5b
> --- /dev/null
> +++ b/arch/arm/xen/hypercall.S
> @@ -0,0 +1,65 @@
> +/******************************************************************************
> + * hypercall.S
> + *
> + * Xen hypercall wrappers
> + *
> + * The Xen hypercall calling convention is very similar to the ARM
> + * procedure calling convention: the first paramter is passed in r0, the
> + * second in r1, the third in r2 and the third in r3. Considering that

I think you meant 'and the fourth in r3'.

So where does the similarity end?  Just in that we use r12?

> + * Xen hypercalls have 5 arguments at most, the fifth paramter is passed
> + * in r4, differently from the procedure calling convention of using the

> + * stack for that case.
> + *
> + * The hypercall number is passed in r12.
> + *
> + * The return value is in r0.
> + *
> + * The hvc ISS is required to be 0xEA1, that is the Xen specific ARM
> + * hypercall tag.
> + *
> + * Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Citrix, 2012
> + */
> +
> +#include <linux/linkage.h>
> +#include <asm/assembler.h>
> +#include <xen/interface/xen.h>
> +
> +
> +/* HVC 0xEA1 */
> +#ifdef CONFIG_THUMB2_KERNEL
> +#define xen_hvc .word 0xf7e08ea1
> +#else
> +#define xen_hvc .word 0xe140ea71
> +#endif
> +
> +/* We need to save and restore r4, because Xen clobbers it. */

Hmm, the comment says r4, but right below I see r12?
Should this comment be by 'privcmd_call'?

> +#define HYPERCALL(hypercall)			\
> +ENTRY(HYPERVISOR_##hypercall)			\
> +	mov r12, #__HYPERVISOR_##hypercall;	\
> +	xen_hvc;							\
> +	mov pc, lr;							\
> +ENDPROC(HYPERVISOR_##hypercall)
> +
> +                .text
> +
> +HYPERCALL(xen_version);
> +HYPERCALL(console_io);
> +HYPERCALL(grant_table_op);
> +HYPERCALL(sched_op);
> +HYPERCALL(event_channel_op);
> +HYPERCALL(hvm_op);
> +HYPERCALL(memory_op);
> +HYPERCALL(physdev_op);
> +
> +ENTRY(privcmd_call)
> +	stmdb	sp!, {r4}
> +	mov r12, r0
> +	mov r0, r1
> +	mov r1, r2
> +	mov r2, r3
> +	ldr r3, [sp, #8]
> +	ldr r4, [sp, #4]
> +	xen_hvc
> +	pop {r4}
> +	mov pc, lr
> +ENDPROC(privcmd_call);
> -- 
> 1.7.2.5
> 
> 
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