RE: [PATCH v9 0/7] Enable Linux guests on Hyper-V on ARM64

[Michael Kelley]

From: Michael Kelley <mikelley@xxxxxxxxxxxxx> Sent: Monday, March 8, 2021 11:57 AM
> 
> This series enables Linux guests running on Hyper-V on ARM64
> hardware. New ARM64-specific code in arch/arm64/hyperv initializes
> Hyper-V, including its interrupts and hypercall mechanism.
> Existing architecture independent drivers for Hyper-V's VMbus and
> synthetic devices just work when built for ARM64. Hyper-V code is
> built and included in the image and modules only if CONFIG_HYPERV
> is enabled.

ARM64 maintainers --

What are the prospects for getting your review and Ack on this patch set?
We're wanting to get the Hyper-V support on ARM64 finally accepted upstream.
Previous comments should be addressed in this revision, with perhaps a
remaining discussion point around the alternate SMCCC hypercall interface
in Patch 1 that makes use of changes in v1.2 of the SMCCC spec.  There are
several viable approaches that I've noted in the patch, depending on
your preferences.

Michael

> 
> The seven patches are organized as follows:
> 
> 1) Update include/linux/arm-smccc.h to provide an HVC wrapper
>    variant that returns results in other than X0 thru X3
> 
> 2) Add definitions and functions for making Hyper-V hypercalls
>    and getting/setting virtual processor registers provided by
>    Hyper-V
> 
> 3) Add architecture specific definitions needed by the
>    architecture independent Hyper-V clocksource driver in
>    drivers/clocksource/hyperv_timer.c. Update the clocksource
>    driver to be initialized on ARM64.
> 
> 4) Add functions needed by the arch independent VMbus driver
>    for reporting a panic to Hyper-V and as stubs for the kexec
>    and crash handlers.
> 
> 5) Add Hyper-V initialization code and utility functions that
>    report Hyper-v status.
> 
> 6) Export screen_info so it may be used by the Hyper-V frame buffer
>    driver built as a module. It is already exported for x86,
>    powerpc, and alpha architectures.
> 
> 7) Make CONFIG_HYPERV selectable on ARM64 in addition to x86/x64.
> 
> Hyper-V on ARM64 runs with a 4 Kbyte page size, but allows guests
> with 4K/16K/64K page size. Linux guests with this ARM64 enablement
> code work with all three supported ARM64 page sizes.
> 
> The Hyper-V vPCI driver at drivers/pci/host/pci-hyperv.c has
> x86/x64-specific code and is not being built for ARM64. Fixing
> this driver to enable vPCI devices on ARM64 will be done later.
> 
> In a few cases, terminology from the x86/x64 world has been carried
> over into the ARM64 code ("MSR", "TSC").  Hyper-V still uses the
> x86/x64 terminology and has not replaced it with something more
> generic, so the code uses the Hyper-V terminology.  This will be
> fixed when Hyper-V updates the usage in the TLFS.
> 
> This patch set is based on the hyperv-next branch of the code tree
> https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/ 
> 
> Changes in v9:
> * Added Patch 1 to enable making an SMCCC compliant hypercall
>   that returns results in other than registers X0 thru X3, per
>   version 1.2 and later of the SMCCC spec.
> * Using the ability to return results in registers X6 and X7,
>   converted hv_get_vpreg_128() to use a "fast" hypercall that
>   passes inputs and outputs in registers, and in doing so eliminated
>   a lot of memory allocation complexity.
> * Cleaned up some extra blank lines and use of spaces in aligning
>   local variables. [Sunil Muthuswamy]
> * Based on discussion about future directions, reverted the
>   population of hv_vp_index array to use a cpuhp state instead
>   of a hypercall, which is like it was in v7 and earlier.
> 
> Changes in v8:
> * Removed a lot of code based on refactoring the boundary between
>   arch independent and arch dependent code for Hyper-V, per comments
>   from Arnd Bergmann. The removed code was either duplicated on
>   the x86 side, or has been folded into architecture independent
>   code as not really being architecture dependent.
> * Added config dependency on !CONFIG_CPU_BIG_ENDIAN [Arnd Bergmann]
> * Reworked the approach to Hyper-V initialization. The functionality
>   is the same, but is now structured like the Xen code with an early
>   init function called in setup_arch() and an early initcall to
>   finish the initialization. [Arnd Bergmann]
> 
> Changes in v7:
> * Separately upstreamed split of hyperv-tlfs.h into arch dependent
>   and independent versions.  In this patch set, update the ARM64
>   hyperv-tlfs.h to include architecture independent definitions.
>   This approach eliminates a lot of lines of otherwise duplicated
>   code on the ARM64 side.
> * Break ARM64 mshyperv.h into smaller pieces. Have an initial
>   baseline, and add code along with patches for a particular
>   functional area. [Marc Zyngier]
> * In mshyperv.h, use static inline functions instead of #defines
>   where possible. [Arnd Bergmann]
> * Use VMbus INTID obtained from ACPI DSDT instead of hardcoding.
>   The STIMER INTID is still hardcoded because it is needed
>   before Linux has initialized the ACPI subsystem, so it can't
>   be obtained from the DSDT.  Wedging it into the GTDT seems
>   dubious, so was not done. [Marc Zyngier]
> * Update Hyper-V page size allocation functions to use
>   alloc_page() if PAGE_SIZE == HV_HYP_PAGE_SIZE [Arnd
>   Bergmann]
> * Various other minor changes based on feedback and to rebase
>   to latest linux-next [Marc Zyngier and Arnd Bergmann]
> 
> Changes in v6:
> * Use SMCCC hypercall interface instead of direct invocation
>   of HVC instruction and the Hyper-V hypercall interface
>   [Marc Zyngier]
> * Reimplemented functions to alloc/free Hyper-V size pages
>   using kmalloc/kfree since kmalloc now guarantees alignment of
>   power of 2 size allocations [Marc Zyngier]
> * Export screen_info in arm64 architecture so it can be used
>   by the Hyper-V buffer driver built as a module
> * Renamed source file arch/arm64/hyperv/hv_init.c to hv_core.c
>   to better reflect its content
> * Fixed the bit position of certain feature flags presented by
>   Hyper-V to the guest.  The bit positions on ARM64 don't match
>   the position on x86 like originally thought.
> * Minor fixups to rebase to 5.6-rc5 linux-next
> 
> Changes in v5:
> * Minor fixups to rebase to 5.4-rc1 linux-next
> 
> Changes in v4:
> * Moved clock-related code into an architecture independent
>   Hyper-V clocksource driver that is already upstream. Clock
>   related code is removed from this patch set except for the
>   ARM64 specific interrupt handler. [Marc Zyngier]
> * Separately upstreamed the split of mshyperv.h into arch independent
>   and arch dependent portions. The arch independent portion has been
>   removed from this patch set.
> * Divided patch #2 of the series into multiple smaller patches
>   [Marc Zyngier]
> * Changed a dozen or so smaller things based on feedback
>   [Marc Zyngier, Will Deacon]
> * Added functions to alloc/free Hyper-V size pages for use by
>   drivers for Hyper-V synthetic devices when updated to not assume
>   guest page size and Hyper-v page size are the same
> 
> Changes in v3:
> * Added initialization of hv_vp_index array like was recently
>   added on x86 branch [KY Srinivasan]
> * Changed Hyper-V ARM64 register symbols to be all uppercase
>   instead of mixed case [KY Srinivasan]
> * Separated mshyperv.h into two files, one architecture
>   independent and one architecture dependent. After this code
>   is upstream, will make changes to the x86 code to use the
>   architecture independent file and remove duplication. And
>   once we have a multi-architecture Hyper-V TLFS, will do a
>   separate patch to split hyperv-tlfs.h in the same way.
>   [KY Srinivasan]
> * Minor tweaks to rebase to latest linux-next code
> 
> Changes in v2:
> * Removed patch to implement slow_virt_to_phys() on ARM64.
>   Use of slow_virt_to_phys() in arch independent Hyper-V
>   drivers has been eliminated by commit 6ba34171bcbd
>   ("Drivers: hv: vmbus: Remove use of slow_virt_to_phys()")
> * Minor tweaks to rebase to latest linux-next code
> *** BLURB HERE ***
> 
> Michael Kelley (7):
>   smccc: Add HVC call variant with result registers other than 0 thru 3
>   arm64: hyperv: Add Hyper-V hypercall and register access utilities
>   arm64: hyperv: Add Hyper-V clocksource/clockevent support
>   arm64: hyperv: Add kexec and panic handlers
>   arm64: hyperv: Initialize hypervisor on boot
>   arm64: efi: Export screen_info
>   Drivers: hv: Enable Hyper-V code to be built on ARM64
> 
>  MAINTAINERS                          |   3 +
>  arch/arm64/Kbuild                    |   1 +
>  arch/arm64/hyperv/Makefile           |   2 +
>  arch/arm64/hyperv/hv_core.c          | 178 +++++++++++++++++++++++++++++++++++
>  arch/arm64/hyperv/mshyperv.c         | 173 ++++++++++++++++++++++++++++++++++
>  arch/arm64/include/asm/hyperv-tlfs.h |  69 ++++++++++++++
>  arch/arm64/include/asm/mshyperv.h    |  72 ++++++++++++++
>  arch/arm64/kernel/efi.c              |   1 +
>  arch/arm64/kernel/setup.c            |   4 +
>  drivers/clocksource/hyperv_timer.c   |  14 +++
>  drivers/hv/Kconfig                   |   3 +-
>  include/linux/arm-smccc.h            |  29 ++++--
>  12 files changed, 542 insertions(+), 7 deletions(-)
>  create mode 100644 arch/arm64/hyperv/Makefile
>  create mode 100644 arch/arm64/hyperv/hv_core.c
>  create mode 100644 arch/arm64/hyperv/mshyperv.c
>  create mode 100644 arch/arm64/include/asm/hyperv-tlfs.h
>  create mode 100644 arch/arm64/include/asm/mshyperv.h
> 
> --
> 1.8.3.1