[PULL,10/25] docs/system: Add recommendations to Hyper-V enlightenments doc

Commit Message

Paolo Bonzini Oct. 15, 2024, 2:16 p.m. UTC

From: Vitaly Kuznetsov <[e-mail]>

While hyperv.rst already has all currently implemented Hyper-V
enlightenments documented, it may be unclear what is the recommended set to
achieve the best result. Add the corresponding section to the doc.

Signed-off-by: Vitaly Kuznetsov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 docs/system/i386/hyperv.rst | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

Patch

diff --git a/docs/system/i386/hyperv.rst b/docs/system/i386/hyperv.rst
index 009947e3914..1c1de77feb6 100644
--- a/docs/system/i386/hyperv.rst
+++ b/docs/system/i386/hyperv.rst
@@ -283,6 +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
 ------------