Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 117 insertions, 0 deletions

diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
new file mode 100644
index 000000000..cf62162d4
--- /dev/null
+++ b/Documentation/virt/kvm/cpuid.rst
@@ -0,0 +1,117 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==============
+KVM CPUID bits
+==============
+
+:Author: Glauber Costa <glommer@gmail.com>
+
+A guest running on a kvm host, can check some of its features using
+cpuid. This is not always guaranteed to work, since userspace can
+mask-out some, or even all KVM-related cpuid features before launching
+a guest.
+
+KVM cpuid functions are:
+
+function: KVM_CPUID_SIGNATURE (0x40000000)
+
+returns::
+
+   eax = 0x40000001
+   ebx = 0x4b4d564b
+   ecx = 0x564b4d56
+   edx = 0x4d
+
+Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
+The value in eax corresponds to the maximum cpuid function present in this leaf,
+and will be updated if more functions are added in the future.
+Note also that old hosts set eax value to 0x0. This should
+be interpreted as if the value was 0x40000001.
+This function queries the presence of KVM cpuid leafs.
+
+function: define KVM_CPUID_FEATURES (0x40000001)
+
+returns::
+
+          ebx, ecx
+          eax = an OR'ed group of (1 << flag)
+
+where ``flag`` is defined as below:
+
+================================== =========== ================================
+flag                               value       meaning
+================================== =========== ================================
+KVM_FEATURE_CLOCKSOURCE            0           kvmclock available at msrs
+                                               0x11 and 0x12
+
+KVM_FEATURE_NOP_IO_DELAY           1           not necessary to perform delays
+                                               on PIO operations
+
+KVM_FEATURE_MMU_OP                 2           deprecated
+
+KVM_FEATURE_CLOCKSOURCE2           3           kvmclock available at msrs
+                                               0x4b564d00 and 0x4b564d01
+
+KVM_FEATURE_ASYNC_PF               4           async pf can be enabled by
+                                               writing to msr 0x4b564d02
+
+KVM_FEATURE_STEAL_TIME             5           steal time can be enabled by
+                                               writing to msr 0x4b564d03
+
+KVM_FEATURE_PV_EOI                 6           paravirtualized end of interrupt
+                                               handler can be enabled by
+                                               writing to msr 0x4b564d04
+
+KVM_FEATURE_PV_UNHALT              7           guest checks this feature bit
+                                               before enabling paravirtualized
+                                               spinlock support
+
+KVM_FEATURE_PV_TLB_FLUSH           9           guest checks this feature bit
+                                               before enabling paravirtualized
+                                               tlb flush
+
+KVM_FEATURE_ASYNC_PF_VMEXIT        10          paravirtualized async PF VM EXIT
+                                               can be enabled by setting bit 2
+                                               when writing to msr 0x4b564d02
+
+KVM_FEATURE_PV_SEND_IPI            11          guest checks this feature bit
+                                               before enabling paravirtualized
+                                               send IPIs
+
+KVM_FEATURE_POLL_CONTROL           12          host-side polling on HLT can
+                                               be disabled by writing
+                                               to msr 0x4b564d05.
+
+KVM_FEATURE_PV_SCHED_YIELD         13          guest checks this feature bit
+                                               before using paravirtualized
+                                               sched yield.
+
+KVM_FEATURE_ASYNC_PF_INT           14          guest checks this feature bit
+                                               before using the second async
+                                               pf control msr 0x4b564d06 and
+                                               async pf acknowledgment msr
+                                               0x4b564d07.
+
+KVM_FEATURE_MSI_EXT_DEST_ID        15          guest checks this feature bit
+                                               before using extended destination
+                                               ID bits in MSI address bits 11-5.
+
+KVM_FEATURE_CLOCKSOURCE_STABLE_BIT 24          host will warn if no guest-side
+                                               per-cpu warps are expected in
+                                               kvmclock
+================================== =========== ================================
+
+::
+
+      edx = an OR'ed group of (1 << flag)
+
+Where ``flag`` here is defined as below:
+
+================== ============ =================================
+flag               value        meaning
+================== ============ =================================
+KVM_HINTS_REALTIME 0            guest checks this feature bit to
+                                determine that vCPUs are never
+                                preempted for an unlimited time
+                                allowing optimizations
+================== ============ =================================