Re: [Xen-devel] [Xen-Devel] [PATCH] [GSOC14] refactored mempaging code from xenpaging to libxc.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/06/14 14:59, Andres Lagar Cavilla wrote:

On Thu, Jun 12, 2014 at 6:22 AM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

On 12/06/14 10:23, Dushyant Behl wrote:
> This patch is part of the work done under the gsoc project -
> Lazy Restore Using Memory Paging.
>
> This patch moves the code to initialize mempaging from xenpaging to libxc.

The source code is named libxc, but technically you are moving it into
libxenguest which is a separate library from libxenctrl.

> The code refractored from xenpaging is the code which sets up paging,
> initializes a shared ring and event channel to communicate with xen. This
> communication is done between the hypervisor and the dom0 tool which performs
> the activity of pager. The xenpaging code is changed to use the newly created
> routines and is tested to properly build and work with this code.
>
> The refractoring is done so that any tool which will act as pager in
> lazy restore or use memory paging can use a same routines to initialize mempaging.
> This refactoring will also allow any future (in-tree) tools to use mempaging.
>
> Signed-off-by: Dushyant Behl <myselfdushyantbehl@xxxxxxxxx>
> Reviewed-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>Â

> ---
> Âtools/libxc/Makefile        Â|  3 +
> Âtools/libxc/xc_mem_paging_setup.c  | 132 ++++++++++++++++++++++++++++++++++++
> Âtools/libxc/xenctrl.h        | Â12 ++++
> Âtools/ocaml/libs/xc/xenctrl_stubs.c | Â11 +--
> Âtools/xenpaging/Makefile      Â|  4 +-
> Âtools/xenpaging/xenpaging.c     | Â93 +++----------------------
> Â6 files changed, 167 insertions(+), 88 deletions(-)
> Âcreate mode 100644 tools/libxc/xc_mem_paging_setup.c
>
> diff --git a/tools/libxc/Makefile b/tools/libxc/Makefile
> index a74b19e..2439853 100644
> --- a/tools/libxc/Makefile
> +++ b/tools/libxc/Makefile
> @@ -69,6 +69,9 @@ GUEST_SRCS-$(CONFIG_ARM) Â Â += xc_dom_armzimageloader.c
> ÂGUEST_SRCS-y         += xc_dom_binloader.c
> ÂGUEST_SRCS-y         += xc_dom_compat_linux.c
>
> +# mem paging setup
> +GUEST_SRCS-y         += xc_mem_paging_setup.c
> +

I don't think you need the comment here. ÂIt is obvious from the name of
the file, although I would suggest you name it "xc_dom_paging.c" or
something a tad less specific.

> ÂGUEST_SRCS-$(CONFIG_X86) Â Â += xc_dom_x86.c
> ÂGUEST_SRCS-$(CONFIG_X86) Â Â += xc_cpuid_x86.c
> ÂGUEST_SRCS-$(CONFIG_X86) Â Â += xc_hvm_build_x86.c
> diff --git a/tools/libxc/xc_mem_paging_setup.c b/tools/libxc/xc_mem_paging_setup.c
> new file mode 100644
> index 0000000..125d203
> --- /dev/null
> +++ b/tools/libxc/xc_mem_paging_setup.c
> @@ -0,0 +1,132 @@
> +/*
> + * tools/libxc/xc_mem_paging_setup.c
> + *
> + * Routines to initialize memory paging. Create shared ring
> + * and event channels to communicate with the hypervisor.
> + *
> + * Copyright (c) 2014 Dushyant Behl
> + * Copyright (c) 2009 by Citrix Systems, Inc. (Patrick Colp)
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ÂSee the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA Â02110-1301 USA
> + */
> +
> +#include "xc_private.h"
> +#include <xen/event_channel.h>
> +#include <xen/mem_event.h>
> +
> +/*
> + * Mem paging ring and event channel setup routine.
> + * Setup a shared ring and an event channel to communicate between
> + * hypervisor and the tool performing mem paging operations.

Please document here, or in the header file, what the error semantics of
the function are. ÂLibxc is a complete mess so these things need
spelling out.

> + */
> +int xc_mem_paging_ring_setup(xc_interface *xch, domid_t domain_id,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âvoid *ring_page, int *port,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âuint32_t *evtchn_port,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âxc_evtchn **xce_handle,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âmem_event_back_ring_t *back_ring)

The parameters should be aligned with the xc_interface.

> +{
> + Â Âint rc;
> + Â Âunsigned long ring_pfn, mmap_pfn;

uint64_t's as these are hvmparams

David Vrabel's GenID series fixes the prototypes of
xc_[gs]et_hvm_param() to be sane.

Andrew, we were thinking this should be rebased onto your git branch for save restore rework, which I assume contains these GenID changes as well. Can you point to the right git coordinates? Thanks

As David and I are both working on our series at the same time, my save/restore is a revision out of date and doesn't yet contain the new prototypes. If you can wait for Davids work to get accepted, I shall rebase and provide a v5.5 or v6.

> +
> + Â Â/* Map the ring page */
> + Â Âxc_get_hvm_param(xch, domain_id, HVM_PARAM_PAGING_RING_PFN, &ring_pfn);
> + Â Âmmap_pfn = ring_pfn;
> + Â Âring_page = xc_map_foreign_batch(xch, domain_id,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ÂPROT_READ | PROT_WRITE, &mmap_pfn, 1);

You are stuffing a pointer into an unsigned long?

ring_page is void * ... mmap_pfn is ulong ....

So it is. I got ring_pfn and ring_page confused.

> + Â Âif ( mmap_pfn & XEN_DOMCTL_PFINFO_XTAB )

What is this check for?

foreign_batch has the old semantics of setting the MSB of the pfn in error. Maybe use map_foreign_bulk with cleaner error reporting?

Eww. That is a nasty interface, and will completely break 32bit toolstacks on machines with hotplug regions above the 8TB boundary.

Please do use map_foreign_bulk().

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel