[Xen-devel] [RFC PATCH v3 00/10] 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. We submit this patch series as an RFC to discuss the
appropriate location for the code and further functionality required to fix the
above concerns.

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 adds additional data-structures and defines to simplify code
readability. Also, this patch series exposes p2m_* macros to access certain PTE
properties in a more readable way. Apart from that, please note that since the
individual functions responsible for walking the guest page tables must support
various details of both AArch32 and AArch64, a simplification of seemingly
identical parts in the affected functions has not always been possible.

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

Cheers,
~Sergej

[0] https://github.com/sergej-proskurin/xen (branch arm-gpt-walk-v3)

Sergej Proskurin (10):
  arm/mem_access: Add (TCR_|TTBCR_)* defines
  arm/mem_access: Add defines holding the width of 32/64bit regs
  arm/mem_access: Add defines supporting PTs with varying page sizes
  arm/mem_access: Add short-descriptor pte typedefs
  arm/p2m: Make PTE helpers publicly available
  arm/mem_access: Introduce GV2M_EXEC permission
  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        | 646 +++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/mem_access.c        |  21 +-
 xen/arch/arm/p2m.c               |  23 --
 xen/include/asm-arm/guest_walk.h |  44 +++
 xen/include/asm-arm/p2m.h        |  27 ++
 xen/include/asm-arm/page.h       | 150 +++++++++
 xen/include/asm-arm/processor.h  |  73 ++++-
 8 files changed, 957 insertions(+), 28 deletions(-)
 create mode 100644 xen/arch/arm/guest_walk.c
 create mode 100644 xen/include/asm-arm/guest_walk.h

-- 
2.12.2


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