[Xen-devel] [PATCH v5 00/12] arm/mem_access: Walk guest page tables in SW if mem_access is active

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

Hi all,

The function p2m_mem_access_check_and_get_page is called from the function
get_page_from_gva if mem_access is active and the hardware-aided translation of
the given guest virtual address (gva) into machine address fails. That is, if
the stage-2 translation tables constrain access to the guests's page tables,
hardware-assisted translation will fail. The idea of the function
p2m_mem_access_check_and_get_page is thus to translate the given gva and check
the requested access rights in software. However, as the current implementation
of p2m_mem_access_check_and_get_page makes use of the hardware-aided gva to ipa
translation, the translation might also fail because of reasons stated above
and will become equally relevant for the altp2m implementation on ARM.  As
such, we provide a software guest translation table walk to address the above
mentioned issue.

The current version of the implementation supports translation of both the
short-descriptor as well as the long-descriptor translation table format on
ARMv7 and ARMv8 (AArch32/AArch64).

This revised version incorporates the comments of the previous patch series and
mainly changes the introduced data-structures and defines to simplify code.
Also, this patch reuses existing code for accessing the guest's memory through
the function vgic_access_guest_memory. In this way, we outsource
safety-relevant checks associated with accessing the guest's memory to one
place and hence simplify potential modification of such.  Please note that this
patch series is based on the second part of Julien Grall's patch series in [1]:
"xen/arm: Move LPAE definition in a separate header".

The following patch series can be found on Github[0].

Cheers,
~Sergej

[0] https://github.com/sergej-proskurin/xen (branch arm-gpt-walk-v5)
[1] https://lists.xen.org/archives/html/xen-devel/2017-06/msg02095.html


Sergej Proskurin (12):
  arm/mem_access: Add and cleanup (TCR_|TTBCR_)* defines
  arm/mem_access: Move PAGE_SHIFT_* macros to lib.h
  arm/mem_access: Add defines supporting PTs with varying page sizes
  arm/lpae: Introduce lpae_page helper
  arm/mem_access: Add short-descriptor pte typedefs and macros
  arm/mem_access: Introduce GV2M_EXEC permission
  arm/mem_access: Introduce BIT_ULL bit operation
  arm/mem_access: Introduce GENMASK_ULL bit operation
  arm/mem_access: Add software guest-page-table walk
  arm/mem_access: Add long-descriptor based gpt
  arm/mem_access: Add short-descriptor based gpt
  arm/mem_access: Walk the guest's pt in software

 xen/arch/arm/Makefile            |   1 +
 xen/arch/arm/guest_walk.c        | 614 +++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/mem_access.c        |  31 +-
 xen/include/asm-arm/bitops.h     |   1 +
 xen/include/asm-arm/config.h     |   2 +
 xen/include/asm-arm/guest_walk.h |  19 ++
 xen/include/asm-arm/lpae.h       |  67 +++++
 xen/include/asm-arm/page.h       |   1 +
 xen/include/asm-arm/processor.h  |  69 ++++-
 xen/include/asm-arm/short-desc.h | 130 +++++++++
 xen/include/xen/bitops.h         |   2 +
 xen/include/xen/iommu.h          |   3 +-
 xen/include/xen/lib.h            |   4 +
 13 files changed, 937 insertions(+), 7 deletions(-)
 create mode 100644 xen/arch/arm/guest_walk.c
 create mode 100644 xen/include/asm-arm/guest_walk.h
 create mode 100644 xen/include/asm-arm/short-desc.h

--
2.13.1


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