[PATCH 3/4] KVM: x86: Omit VCPU_REGS_RIP from emulator's _regs array

[Sean Christopherson <seanjc@google.com>]

Omit RIP from the emulator's _regs array, which is used only for GPRs,
i.e. registers that can be referenced via ModRM and/or SIB bytes.  The
emulator uses the dedicated _eip field for RIP, and manually reads from
_eip to handle RIP-relative addressing.

Replace all open coded instances of '16' with the new NR_EMULATOR_GPRS.

See also the comments above the read_gpr() and write_gpr() declarations,
and obviously the handling in writeback_registers().

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/emulate.c     | 12 ++++++------
 arch/x86/kvm/kvm_emulate.h | 10 +++++++++-
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index c58366ae4da2..dd1bf116a9ed 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -247,8 +247,8 @@ enum x86_transfer_type {
 
 static ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr)
 {
-	if (WARN_ON_ONCE(nr >= 16))
-		nr &= 16 - 1;
+	if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))
+		nr &= NR_EMULATOR_GPRS - 1;
 
 	if (!(ctxt->regs_valid & (1 << nr))) {
 		ctxt->regs_valid |= 1 << nr;
@@ -259,8 +259,8 @@ static ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr)
 
 static ulong *reg_write(struct x86_emulate_ctxt *ctxt, unsigned nr)
 {
-	if (WARN_ON_ONCE(nr >= 16))
-		nr &= 16 - 1;
+	if (WARN_ON_ONCE(nr >= NR_EMULATOR_GPRS))
+		nr &= NR_EMULATOR_GPRS - 1;
 
 	ctxt->regs_valid |= 1 << nr;
 	ctxt->regs_dirty |= 1 << nr;
@@ -278,7 +278,7 @@ static void writeback_registers(struct x86_emulate_ctxt *ctxt)
 	unsigned long dirty = ctxt->regs_dirty;
 	unsigned reg;
 
-	for_each_set_bit(reg, &dirty, 16)
+	for_each_set_bit(reg, &dirty, NR_EMULATOR_GPRS)
 		ctxt->ops->write_gpr(ctxt, reg, ctxt->_regs[reg]);
 }
 
@@ -2495,7 +2495,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 	u16 selector;
 	int i, r;
 
-	for (i = 0; i < 16; i++)
+	for (i = 0; i < NR_EMULATOR_GPRS; i++)
 		*reg_write(ctxt, i) = GET_SMSTATE(u64, smstate, 0x7ff8 - i * 8);
 
 	ctxt->_eip   = GET_SMSTATE(u64, smstate, 0x7f78);
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 8dff25d267b7..bdd4e9865ca9 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -301,6 +301,14 @@ struct fastop;
 
 typedef void (*fastop_t)(struct fastop *);
 
+/*
+ * The emulator's _regs array tracks only the GPRs, i.e. excludes RIP.  RIP is
+ * tracked/accessed via _eip, and except for RIP relative addressing, which
+ * also uses _eip, RIP cannot be a register operand nor can it be an operand in
+ * a ModRM or SIB byte.
+ */
+#define NR_EMULATOR_GPRS	(VCPU_REGS_R15 + 1)
+
 struct x86_emulate_ctxt {
 	void *vcpu;
 	const struct x86_emulate_ops *ops;
@@ -363,7 +371,7 @@ struct x86_emulate_ctxt {
 	struct operand src2;
 	struct operand dst;
 	struct operand memop;
-	unsigned long _regs[NR_VCPU_REGS];
+	unsigned long _regs[NR_EMULATOR_GPRS];
 	struct operand *memopp;
 	struct fetch_cache fetch;
 	struct read_cache io_read;
-- 
2.36.1.124.g0e6072fb45-goog