[PATCH v4 1/5] KVM: x86: Widen x86_exception's error_code to 64 bits

[Sean Christopherson <seanjc@google.com>]

From: Kevin Cheng <chengkev@google.com>

Widen the error_code field in struct x86_exception from u16 to u64 to
accommodate AMD's NPF error code, which defines information bits above
bit 31, e.g. PFERR_GUEST_FINAL_MASK (bit 32), and PFERR_GUEST_PAGE_MASK
(bit 33).

Retain the u16 type for the local errcode variable in walk_addr_generic
as the walker synthesizes conventional #PF error codes that are
architecturally limited to bits 15:0.

Signed-off-by: Kevin Cheng <chengkev@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/kvm_emulate.h     | 2 +-
 arch/x86/kvm/mmu/paging_tmpl.h | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 72aece9ef575..f5df31a52996 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -22,7 +22,7 @@ enum x86_intercept_stage;
 struct x86_exception {
 	u8 vector;
 	bool error_code_valid;
-	u16 error_code;
+	u64 error_code;
 	bool nested_page_fault;
 	union {
 		u64 address; /* cr2 or nested page fault gpa */
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 07100bbfc270..51f8b4522314 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -328,6 +328,12 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 	const int write_fault = access & PFERR_WRITE_MASK;
 	const int user_fault  = access & PFERR_USER_MASK;
 	const int fetch_fault = access & PFERR_FETCH_MASK;
+	/*
+	 * Note! Track the error_code that's common to legacy shadow paging
+	 * and NPT shadow paging as a u16 to guard against unintentionally
+	 * setting any of bits 63:16.  Architecturally, the #PF error code is
+	 * 32 bits, and Intel CPUs don't support settings bits 31:16.
+	 */
 	u16 errcode = 0;
 	gpa_t real_gpa;
 	gfn_t gfn;
-- 
2.54.0.794.g4f17f83d09-goog