fix: KVM: x86: Use gpa_t for cr2/gpa to fix TDP support on 32-bit (v5.6)

fix: KVM: x86: Use gpa_t for cr2/gpa to fix TDP support on 32-bit (v5.6)

See upstream commit :

  commit 736c291c9f36b07f8889c61764c28edce20e715d
  Author: Sean Christopherson <sean.j.christopherson@intel.com>
  Date:   Fri Dec 6 15:57:14 2019 -0800

    KVM: x86: Use gpa_t for cr2/gpa to fix TDP support on 32-bit KVM

    Convert a plethora of parameters and variables in the MMU and page fault
    flows from type gva_t to gpa_t to properly handle TDP on 32-bit KVM.

    Thanks to PSE and PAE paging, 32-bit kernels can access 64-bit physical
    addresses.  When TDP is enabled, the fault address is a guest physical
    address and thus can be a 64-bit value, even when both KVM and its guest
    are using 32-bit virtual addressing, e.g. VMX's VMCS.GUEST_PHYSICAL is a
    64-bit field, not a natural width field.

    Using a gva_t for the fault address means KVM will incorrectly drop the
    upper 32-bits of the GPA.  Ditto for gva_to_gpa() when it is used to
    translate L2 GPAs to L1 GPAs.

    Opportunistically rename variables and parameters to better reflect the
    dual address modes, e.g. use "cr2_or_gpa" for fault addresses and plain
    "addr" instead of "vaddr" when the address may be either a GVA or an L2
    GPA.  Similarly, use "gpa" in the nonpaging_page_fault() flows to avoid
    a confusing "gpa_t gva" declaration; this also sets the stage for a
    future patch to combing nonpaging_page_fault() and tdp_page_fault() with
    minimal churn.

    Sprinkle in a few comments to document flows where an address is known
    to be a GVA and thus can be safely truncated to a 32-bit value.  Add
    WARNs in kvm_handle_page_fault() and FNAME(gva_to_gpa_nested)() to help
    document such cases and detect bugs.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>