Merge tag 'for-upstream' of https://gitlab.com/bonzini/qemu into staging

* tcg/s390x: Fix for TSTEQ/TSTNE
* target/i386: Fixes for IN and OUT with REX prefix
* target/i386: New CPUID features and logic fixes
* target/i386: Add support save/load HWCR MSR
* target/i386: Move more instructions to new decoder; separate decoding
  and IR generation
* target/i386/tcg: Use DPL-level accesses for interrupts and call gates
* accel/kvm: perform capability checks on VM file descriptor when necessary
* accel/kvm: dynamically sized kvm memslots array
* target/i386: fixes for Hyper-V
* docs/system: Add recommendations to Hyper-V enlightenments doc

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* tag 'for-upstream' of https://gitlab.com/bonzini/qemu: (26 commits)
  target/i386: Use only 16 and 32-bit operands for IN/OUT
  accel/kvm: check for KVM_CAP_MEMORY_ATTRIBUTES on vm
  accel/kvm: check for KVM_CAP_MULTI_ADDRESS_SPACE on vm
  accel/kvm: check for KVM_CAP_READONLY_MEM on VM
  target/i386/tcg: Use DPL-level accesses for interrupts and call gates
  KVM: Rename KVMState->nr_slots to nr_slots_max
  KVM: Rename KVMMemoryListener.nr_used_slots to nr_slots_used
  KVM: Define KVM_MEMSLOTS_NUM_MAX_DEFAULT
  KVM: Dynamic sized kvm memslots array
  target/i386: assert that cc_op* and pc_save are preserved
  target/i386: list instructions still in translate.c
  target/i386: do not check PREFIX_LOCK in old-style decoder
  target/i386: convert CMPXCHG8B/CMPXCHG16B to new decoder
  target/i386: decode address before going back to translate.c
  target/i386: convert bit test instructions to new decoder
  tcg/s390x: fix constraint for 32-bit TSTEQ/TSTNE
  docs/system: Add recommendations to Hyper-V enlightenments doc
  target/i386: Make sure SynIC state is really updated before KVM_RUN
  target/i386: Exclude 'hv-syndbg' from 'hv-passthrough'
  target/i386: Fix conditional CONFIG_SYNDBG enablement
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 39 insertions, 4 deletions

diff --git a/docs/system/i386/hyperv.rst b/docs/system/i386/hyperv.rst
index 2505dc4c86..1c1de77feb 100644
--- a/docs/system/i386/hyperv.rst
+++ b/docs/system/i386/hyperv.rst
@@ -262,14 +262,19 @@ Supplementary features
 ``hv-passthrough``
   In some cases (e.g. during development) it may make sense to use QEMU in
   'pass-through' mode and give Windows guests all enlightenments currently
-  supported by KVM. This pass-through mode is enabled by "hv-passthrough" CPU
-  flag.
+  supported by KVM.
 
   Note: ``hv-passthrough`` flag only enables enlightenments which are known to QEMU
   (have corresponding 'hv-' flag) and copies ``hv-spinlocks`` and ``hv-vendor-id``
   values from KVM to QEMU. ``hv-passthrough`` overrides all other 'hv-' settings on
-  the command line. Also, enabling this flag effectively prevents migration as the
-  list of enabled enlightenments may differ between target and destination hosts.
+  the command line.
+
+  Note: ``hv-passthrough`` does not enable ``hv-syndbg`` which can prevent certain
+  Windows guests from booting when used without proper configuration. If needed,
+  ``hv-syndbg`` can be enabled additionally.
+
+  Note: ``hv-passthrough`` effectively prevents migration as the list of enabled
+  enlightenments may differ between target and destination hosts.
 
 ``hv-enforce-cpuid``
   By default, KVM allows the guest to use all currently supported Hyper-V
@@ -278,6 +283,36 @@ Supplementary features
   feature alters this behavior and only allows the guest to use exposed Hyper-V
   enlightenments.
 
+Recommendations
+---------------
+
+To achieve the best performance of Windows and Hyper-V guests and unless there
+are any specific requirements (e.g. migration to older QEMU/KVM versions,
+emulating specific Hyper-V version, ...), it is recommended to enable all
+currently implemented Hyper-V enlightenments with the following exceptions:
+
+- ``hv-syndbg``, ``hv-passthrough``, ``hv-enforce-cpuid`` should not be enabled
+  in production configurations as these are debugging/development features.
+- ``hv-reset`` can be avoided as modern Hyper-V versions don't expose it.
+- ``hv-evmcs`` can (and should) be enabled on Intel CPUs only. While the feature
+  is only used in nested configurations (Hyper-V, WSL2), enabling it for regular
+  Windows guests should not have any negative effects.
+- ``hv-no-nonarch-coresharing`` must only be enabled if vCPUs are properly pinned
+  so no non-architectural core sharing is possible.
+- ``hv-vendor-id``, ``hv-version-id-build``, ``hv-version-id-major``,
+  ``hv-version-id-minor``, ``hv-version-id-spack``, ``hv-version-id-sbranch``,
+  ``hv-version-id-snumber`` can be left unchanged, guests are not supposed to
+  behave differently when different Hyper-V version is presented to them.
+- ``hv-crash`` must only be enabled if the crash information is consumed via
+  QAPI by higher levels of the virtualization stack. Enabling this feature
+  effectively prevents Windows from creating dumps upon crashes.
+- ``hv-reenlightenment`` can only be used on hardware which supports TSC
+  scaling or when guest migration is not needed.
+- ``hv-spinlocks`` should be set to e.g. 0xfff when host CPUs are overcommited
+  (meaning there are other scheduled tasks or guests) and can be left unchanged
+  from the default value (0xffffffff) otherwise.
+- ``hv-avic``/``hv-apicv`` should not be enabled if the hardware does not
+  support APIC virtualization (Intel APICv, AMD AVIC).
 
 Useful links
 ------------