Re: [Xen-devel] [PATCH v4 02/24] xen/arm: hypercalls

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 14 Sep 2012, Marc Zyngier wrote:
> On 14/09/12 12:13, 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.
> > 
> > 
> > Changes in v2:
> > - define an HYPERCALL macro for 5 arguments hypercall wrappers, even if
> > at the moment is unused;
> > - use ldm instead of pop;
> > - fix up comments.
> > 
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >  arch/arm/include/asm/xen/hypercall.h |   50 ++++++++++++++++
> >  arch/arm/xen/Makefile                |    2 +-
> >  arch/arm/xen/hypercall.S             |  106 
> > ++++++++++++++++++++++++++++++++++
> >  3 files changed, 157 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@xxxxxxxxxxxxx>, 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..074f5ed
> > --- /dev/null
> > +++ b/arch/arm/xen/hypercall.S
> > @@ -0,0 +1,106 @@
> > +/******************************************************************************
> > + * hypercall.S
> > + *
> > + * Xen hypercall wrappers
> > + *
> > + * Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, 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.
> > + */
> > +
> > +/*
> > + * 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 fourth in r3. Considering that
> > + * 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.
> > + */
> > +
> > +#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
> 
> You should consider using Dave Martin's opcode injection series for
> that. The patches are already in Russell's for-next branch.

I am all for using Dave's patches and I have even already sent a patch
to change the wrappers to use __HVC:

http://marc.info/?l=linux-kernel&m=134513261623427&w=2

I have only temporarely dropped it, only to reduce the amount of
external dependencies of this series. It already depends on Konrad's
stable/for-linus-3.7, so I would rather send this patch out later on its
own...

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