KVM: x86: Improve documentation of MSR_KVM_ASYNC_PF_EN

Fix some incorrect statement of MSR_KVM_ASYNC_PF_EN documentation and
state clearly the token in 'struct kvm_vcpu_pv_apf_data' of 'page ready'
event is matchted with the token in CR2 in 'page not present' event.
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20231025055914.1201792-3-xiaoyao.li@intel.comSigned-off-by: Sean Christopherson <seanjc@google.com>

Documentation/virt/kvm/x86/msr.rst

@@ -193,8 +193,8 @@ data:
 	Asynchronous page fault (APF) control MSR.
 
 	Bits 63-6 hold 64-byte aligned physical address of a 64 byte memory area
-	which must be in guest RAM and must be zeroed. This memory is expected
-	to hold a copy of the following structure::
+	which must be in guest RAM. This memory is expected to hold the
+	following structure::
 
 	  struct kvm_vcpu_pv_apf_data {
 		/* Used for 'page not present' events delivered via #PF */
@@ -231,14 +231,14 @@ data:
 	as regular page fault, guest must reset 'flags' to '0' before it does
 	something that can generate normal page fault.
 
-	Bytes 5-7 of 64 byte memory location ('token') will be written to by the
+	Bytes 4-7 of 64 byte memory location ('token') will be written to by the
 	hypervisor at the time of APF 'page ready' event injection. The content
-	of these bytes is a token which was previously delivered as 'page not
-	present' event. The event indicates the page in now available. Guest is
-	supposed to write '0' to 'token' when it is done handling 'page ready'
-	event and to write 1' to MSR_KVM_ASYNC_PF_ACK after clearing the location;
-	writing to the MSR forces KVM to re-scan its queue and deliver the next
-	pending notification.
+	of these bytes is a token which was previously delivered in CR2 as
+	'page not present' event. The event indicates the page is now available.
+	Guest is supposed to write '0' to 'token' when it is done handling
+	'page ready' event and to write '1' to MSR_KVM_ASYNC_PF_ACK after
+	clearing the location; writing to the MSR forces KVM to re-scan its
+	queue and deliver the next pending notification.
 
 	Note, MSR_KVM_ASYNC_PF_INT MSR specifying the interrupt vector for 'page
 	ready' APF delivery needs to be written to before enabling APF mechanism