[Xen-devel] [PATCH v3 0/2] Support consistent reads of mapped vcpu_runstate_info

[Juergen Gross <jgross@xxxxxxxx>]

There has been a report about incorrect vruntime accounting in Linux
guests under Xen. A Linux kernel with CONFIG_PARAVIRT_TIME_ACCOUNTING
set is capable to do correct vruntime accounting, but this would
require the kernel to be able to read the runstate data of other cpus.

A guest mapping vcpu_runstate_info into its memory can't read this
information from another cpu but the one the data is referring to.
Reason is there is no reliable way for the guest to detect a concurrent
data update by the hypervisor.

This patch series adds an update flag to the mapped data which can be
used by the guest to detect an update is occurring. As this flag is
modifying the current interface it has to be activated by using a
vm_assist hypercall, which in turn has to be made available for ARM.

Runtime tested on x86 with a modified Linux kernel using the new
feature.
Compile tested only for ARM.

Changes in V3:
- patch 2: simplify update_runstate_area() address calculation as
  requested by Jan Beulich

Changes in V2:
- patch 1: readded the #ifdef's as requested by Jan Beulich
- patch 2: smp_wmb() instead of wmb() as requested by Andrew Cooper
- patch 2: use sizeof() as requested by Jan Beulich
- patch 2: eliminate new variable update_flag as requested by Jan Beulich

Juergen Gross (2):
  xen/arm: add support for vm_assist hypercall
  xen: add update indicator to vcpu_runstate_info

 xen/arch/arm/domain.c        | 20 ++++++++++++++++++++
 xen/arch/arm/traps.c         |  1 +
 xen/arch/x86/domain.c        | 21 +++++++++++++++++++++
 xen/include/asm-arm/config.h |  2 ++
 xen/include/asm-x86/config.h |  1 +
 xen/include/public/vcpu.h    |  6 ++++++
 xen/include/public/xen.h     |  7 +++++++
 7 files changed, 58 insertions(+)

-- 
2.6.6


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