KVM: Documentation: Fix documentation for nested.

Nested VMX was enabled by default in commit 1e58e5e5 ("KVM:
VMX: enable nested virtualization by default"), which was merged
in Linux 4.20. This patch is to fix the documentation accordingly.
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Message-Id: <20210128154747.4242-1-yu.c.zhang@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/nested-vmx.rst

@@ -37,8 +37,10 @@ call L2.
 Running nested VMX
 ------------------
 
-The nested VMX feature is disabled by default. It can be enabled by giving
-the "nested=1" option to the kvm-intel module.
+The nested VMX feature is enabled by default since Linux kernel v4.20. For
+older Linux kernel, it can be enabled by giving the "nested=1" option to the
+kvm-intel module.
+
 
 No modifications are required to user space (qemu). However, qemu's default
 emulated CPU type (qemu64) does not list the "VMX" CPU feature, so it must be

Documentation/virt/kvm/running-nested-guests.rst

@@ -74,7 +74,7 @@ few:
 Enabling "nested" (x86)
 -----------------------
 
-From Linux kernel v4.19 onwards, the ``nested`` KVM parameter is enabled
+From Linux kernel v4.20 onwards, the ``nested`` KVM parameter is enabled
 by default for Intel and AMD.  (Though your Linux distribution might
 override this default.)