Documentation: move Documentation/virtual to Documentation/virt

Renaming docs seems to be en vogue at the moment, so fix on of the
grossly misnamed directories.  We usually never use "virtual" as
a shortcut for virtualization in the kernel, but always virt,
as seen in the virt/ top-level directory.  Fix up the documentation
to match that.

Fixes: ed16648eb5b8 ("Move kvm, uml, and lguest subdirectories under a common "virtual" directory, I.E:")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 107 insertions, 0 deletions

diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
new file mode 100644
index 000000000000..01b081f6e7ea
--- /dev/null
+++ b/Documentation/virt/kvm/cpuid.rst
@@ -0,0 +1,107 @@
+.. 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_UNHAULT            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
+                                              sebd IPIs
+
+KVM_FEATURE_PV_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_CLOCSOURCE_STABLE_BIT 24          host will warn if no guest-side
+                                              per-cpu warps are expeced 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
+================== ============ =================================