[Xen-devel] [PATCH RFCv3 0/8] toolstack-based approach to pvhvm guest kexec

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

Changes from RFC/WIPv2:

Here is a slightly different approach to memory reassignment. Instead of
introducing new (and very doubtful) XENMEM_transfer operation introduce
simple XEN_DOMCTL_set_recipient operation and do everything in 
free_domheap_pages()
handler utilizing normal domain destroy path. This is better because:
- The approach is general-enough
- All memory pages are usually being freed when the domain is destroyed
- No special grants handling required
- Better supportability

With regards to PV:
Though XEN_DOMCTL_set_recipient works for both PV and HVM this patchset does not
bring PV kexec/kdump support. xc_domain_soft_reset() is limited to work with HVM
domains only. The main reason for that is: it is (in theory) possible to save 
p2m
and rebuild them with the new domain but that would only allow us to resume 
execution
from where we stopped. If we want to execute new kernel we need to build the 
same
kernel/initrd/bootstrap_pagetables/... structure we build to boot PV domain 
initially.
That however would destroy the original domain's memory thus making kdump 
impossible.
To make everything work additional support from kexec userspace/linux kernel is
required and I'm not sure it makes sense to implement all this stuff in the 
light of
PVH.

Original description:

When a PVHVM linux guest performs kexec there are lots of things which
require taking care of:
- shared info, vcpu_info
- grants
- event channels
- ...
Instead of taking care of all these things we can rebuild the domain
performing kexec from scratch doing so-called soft-reboot.

The idea was suggested by David Vrabel, Jan Beulich, and Konrad Rzeszutek Wilk.

P.S. The patch series can be tested with PVHVM Linux guest with the following
modifications:

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c0cb11f..33c5cdd 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -33,6 +33,10 @@
 #include <linux/memblock.h>
 #include <linux/edd.h>

+#ifdef CONFIG_KEXEC
+#include <linux/kexec.h>
+#endif
+
 #include <xen/xen.h>
 #include <xen/events.h>
 #include <xen/interface/xen.h>
@@ -1810,6 +1814,22 @@ static struct notifier_block xen_hvm_cpu_notifier = {
   .notifier_call   = xen_hvm_cpu_notify,
 };

+#ifdef CONFIG_KEXEC
+static void xen_pvhvm_kexec_shutdown(void)
+{
+       native_machine_shutdown();
+       if (kexec_in_progress) {
+          xen_reboot(SHUTDOWN_soft_reset);
+          }
+}
+
+static void xen_pvhvm_crash_shutdown(struct pt_regs *regs)
+{
+       native_machine_crash_shutdown(regs);
+       xen_reboot(SHUTDOWN_soft_reset);
+}
+#endif
+
 static void __init xen_hvm_guest_init(void)
 {
        init_hvm_pv_info();
@@ -1826,6 +1846,10 @@ static void __init xen_hvm_guest_init(void)
   x86_init.irqs.intr_init = xen_init_IRQ;
   xen_hvm_init_time_ops();
   xen_hvm_init_mmu_ops();
+#ifdef CONFIG_KEXEC
+       machine_ops.shutdown = xen_pvhvm_kexec_shutdown;
+       machine_ops.crash_shutdown = xen_pvhvm_crash_shutdown;
+#endif
 }

 static bool xen_nopv = false;
diff --git a/include/xen/interface/sched.h b/include/xen/interface/sched.h
index 9ce0839..b5942a8 100644
--- a/include/xen/interface/sched.h
+++ b/include/xen/interface/sched.h
@@ -107,5 +107,6 @@ struct sched_watchdog {
 #define SHUTDOWN_suspend    2  /* Clean up, save suspend info, kill.         */
 #define SHUTDOWN_crash      3  /* Tell controller we've crashed.             */
 #define SHUTDOWN_watchdog   4  /* Restart because watchdog time expired.     */
+#define SHUTDOWN_soft_reset 5  /* Soft-reset for kexec.                      */

 #endif /* __XEN_PUBLIC_SCHED_H__ */

Vitaly Kuznetsov (8):
  xen: introduce SHUTDOWN_soft_reset shutdown reason
  libxl: support SHUTDOWN_soft_reset shutdown reason
  xen: introduce XEN_DOMCTL_set_recipient
  libxc: support XEN_DOMCTL_set_recipient
  libxl: add libxl__domain_soft_reset_destroy_old()
  libxc: introduce soft reset for HVM domains
  libxl: soft reset support
  xsm: add XEN_DOMCTL_set_recipient support

 tools/libxc/Makefile                |   1 +
 tools/libxc/xc_domain.c             |  10 +
 tools/libxc/xc_domain_soft_reset.c  | 394 ++++++++++++++++++++++++++++++++++++
 tools/libxc/xenctrl.h               |  14 ++
 tools/libxc/xenguest.h              |  20 ++
 tools/libxl/libxl.c                 |  32 ++-
 tools/libxl/libxl.h                 |   6 +
 tools/libxl/libxl_create.c          | 103 +++++++++-
 tools/libxl/libxl_internal.h        |   8 +
 tools/libxl/libxl_types.idl         |   1 +
 tools/libxl/xl_cmdimpl.c            |  24 ++-
 tools/python/xen/lowlevel/xl/xl.c   |   1 +
 xen/common/domain.c                 |   3 +
 xen/common/domctl.c                 |  35 ++++
 xen/common/page_alloc.c             |  26 ++-
 xen/common/shutdown.c               |   7 +
 xen/include/public/domctl.h         |  19 ++
 xen/include/public/sched.h          |   3 +-
 xen/include/xen/sched.h             |   1 +
 xen/include/xsm/dummy.h             |   6 +
 xen/include/xsm/xsm.h               |   6 +
 xen/xsm/dummy.c                     |   1 +
 xen/xsm/flask/hooks.c               |  17 ++
 xen/xsm/flask/policy/access_vectors |  10 +
 24 files changed, 726 insertions(+), 22 deletions(-)
 create mode 100644 tools/libxc/xc_domain_soft_reset.c

-- 
1.9.3


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