MIPS: KVM: Fix NULL pointer dereference

After commit 45c7e8af4a5e3f0bea4ac209 ("MIPS: Remove KVM_TE support") we
get a NULL pointer dereference when creating a KVM guest:

[ 146.243409] Starting KVM with MIPS VZ extensions
[ 149.849151] CPU 3 Unable to handle kernel paging request at virtual address 0000000000000300, epc == ffffffffc06356ec, ra == ffffffffc063568c
[ 149.849177] Oops[#1]:
[ 149.849182] CPU: 3 PID: 2265 Comm: qemu-system-mip Not tainted 6.4.0-rc3+ #1671
[ 149.849188] Hardware name: THTF CX TL630 Series/THTF-LS3A4000-7A1000-ML4A, BIOS KL4.1F.TF.D.166.201225.R 12/25/2020
[ 149.849192] $ 0 : 0000000000000000 000000007400cce0 0000000000400004 ffffffff8119c740
[ 149.849209] $ 4 : 000000007400cce1 000000007400cce1 0000000000000000 0000000000000000
[ 149.849221] $ 8 : 000000240058bb36 ffffffff81421ac0 0000000000000000 0000000000400dc0
[ 149.849233] $12 : 9800000102a07cc8 ffffffff80e40e38 0000000000000001 0000000000400dc0
[ 149.849245] $16 : 0000000000000000 9800000106cd0000 9800000106cd0000 9800000100cce000
[ 149.849257] $20 : ffffffffc0632b28 ffffffffc05b31b0 9800000100ccca00 0000000000400000
[ 149.849269] $24 : 9800000106cd09ce ffffffff802f69d0
[ 149.849281] $28 : 9800000102a04000 9800000102a07cd0 98000001106a8000 ffffffffc063568c
[ 149.849293] Hi : 00000335b2111e66
[ 149.849295] Lo : 6668d90061ae0ae9
[ 149.849298] epc : ffffffffc06356ec kvm_vz_vcpu_setup+0xc4/0x328 [kvm]
[ 149.849324] ra : ffffffffc063568c kvm_vz_vcpu_setup+0x64/0x328 [kvm]
[ 149.849336] Status: 7400cce3 KX SX UX KERNEL EXL IE
[ 149.849351] Cause : 1000000c (ExcCode 03)
[ 149.849354] BadVA : 0000000000000300
[ 149.849357] PrId : 0014c004 (ICT Loongson-3)
[ 149.849360] Modules linked in: kvm nfnetlink_queue nfnetlink_log nfnetlink fuse sha256_generic libsha256 cfg80211 rfkill binfmt_misc vfat fat snd_hda_codec_hdmi input_leds led_class snd_hda_intel snd_intel_dspcfg snd_hda_codec snd_hda_core snd_pcm snd_timer snd serio_raw xhci_pci radeon drm_suballoc_helper drm_display_helper xhci_hcd ip_tables x_tables
[ 149.849432] Process qemu-system-mip (pid: 2265, threadinfo=00000000ae2982d2, task=0000000038e09ad4, tls=000000ffeba16030)
[ 149.849439] Stack : 9800000000000003 9800000100ccca00 9800000100ccc000 ffffffffc062cef4
[ 149.849453] 9800000102a07d18 c89b63a7ab338e00 0000000000000000 ffffffff811a0000
[ 149.849465] 0000000000000000 9800000106cd0000 ffffffff80e59938 98000001106a8920
[ 149.849476] ffffffff80e57f30 ffffffffc062854c ffffffff811a0000 9800000102bf4240
[ 149.849488] ffffffffc05b0000 ffffffff80e3a798 000000ff78000000 000000ff78000010
[ 149.849500] 0000000000000255 98000001021f7de0 98000001023f0078 ffffffff81434000
[ 149.849511] 0000000000000000 0000000000000000 9800000102ae0000 980000025e92ae28
[ 149.849523] 0000000000000000 c89b63a7ab338e00 0000000000000001 ffffffff8119dce0
[ 149.849535] 000000ff78000010 ffffffff804f3d3c 9800000102a07eb0 0000000000000255
[ 149.849546] 0000000000000000 ffffffff8049460c 000000ff78000010 0000000000000255
[ 149.849558] ...
[ 149.849565] Call Trace:
[ 149.849567] [<ffffffffc06356ec>] kvm_vz_vcpu_setup+0xc4/0x328 [kvm]
[ 149.849586] [<ffffffffc062cef4>] kvm_arch_vcpu_create+0x184/0x228 [kvm]
[ 149.849605] [<ffffffffc062854c>] kvm_vm_ioctl+0x64c/0xf28 [kvm]
[ 149.849623] [<ffffffff805209c0>] sys_ioctl+0xc8/0x118
[ 149.849631] [<ffffffff80219eb0>] syscall_common+0x34/0x58

The root cause is the deletion of kvm_mips_commpage_init() leaves vcpu
->arch.cop0 NULL. So fix it by making cop0 from a pointer to an embedded
object.

Fixes: 45c7e8af4a5e3f0bea4ac209 ("MIPS: Remove KVM_TE support")
Cc: [e-mail]
Reported-by: Yu Zhao <[e-mail]>
Suggested-by: Thomas Bogendoerfer <[e-mail]>
Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>
Signed-off-by: Huacai Chen <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/include/asm/kvm_host.h

···
 	unsigned int aux_inuse;
 
 	/* COP0 State */
-	struct mips_coproc *cop0;
+	struct mips_coproc cop0;
 
 	/* Resume PC after MMIO completion */
 	unsigned long io_pc;
···
 static inline bool kvm_mips_guest_has_fpu(struct kvm_vcpu_arch *vcpu)
 {
 	return kvm_mips_guest_can_have_fpu(vcpu) &&
-		kvm_read_c0_guest_config1(vcpu->cop0) & MIPS_CONF1_FP;
+		kvm_read_c0_guest_config1(&vcpu->cop0) & MIPS_CONF1_FP;
 }
 
 static inline bool kvm_mips_guest_can_have_msa(struct kvm_vcpu_arch *vcpu)
···
 static inline bool kvm_mips_guest_has_msa(struct kvm_vcpu_arch *vcpu)
 {
 	return kvm_mips_guest_can_have_msa(vcpu) &&
-		kvm_read_c0_guest_config3(vcpu->cop0) & MIPS_CONF3_MSA;
+		kvm_read_c0_guest_config3(&vcpu->cop0) & MIPS_CONF3_MSA;
 }
 
 struct kvm_mips_callbacks {

arch/mips/kvm/emulate.c

···
  */
 int kvm_mips_count_disabled(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 
 	return	(vcpu->arch.count_ctl & KVM_REG_MIPS_COUNT_CTL_DC) ||
 		(kvm_read_c0_guest_cause(cop0) & CAUSEF_DC);
···
  */
 static u32 kvm_mips_read_count_running(struct kvm_vcpu *vcpu, ktime_t now)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	ktime_t expires, threshold;
 	u32 count, compare;
 	int running;
···
  */
 u32 kvm_mips_read_count(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 
 	/* If count disabled just read static copy of count */
 	if (kvm_mips_count_disabled(vcpu))
···
 static void kvm_mips_resume_hrtimer(struct kvm_vcpu *vcpu,
 				    ktime_t now, u32 count)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	u32 compare;
 	u64 delta;
 	ktime_t expire;
···
  */
 void kvm_mips_write_count(struct kvm_vcpu *vcpu, u32 count)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	ktime_t now;
 
 	/* Calculate bias */
···
  */
 int kvm_mips_set_count_hz(struct kvm_vcpu *vcpu, s64 count_hz)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	int dc;
 	ktime_t now;
 	u32 count;
···
  */
 void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	int dc;
 	u32 old_compare = kvm_read_c0_guest_compare(cop0);
 	s32 delta = compare - old_compare;
···
  */
 static ktime_t kvm_mips_count_disable(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	u32 count;
 	ktime_t now;
 
···
  */
 void kvm_mips_count_disable_cause(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 
 	kvm_set_c0_guest_cause(cop0, CAUSEF_DC);
 	if (!(vcpu->arch.count_ctl & KVM_REG_MIPS_COUNT_CTL_DC))
···
  */
 void kvm_mips_count_enable_cause(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	u32 count;
 
 	kvm_clear_c0_guest_cause(cop0, CAUSEF_DC);
···
  */
 int kvm_mips_set_count_ctl(struct kvm_vcpu *vcpu, s64 count_ctl)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	s64 changed = count_ctl ^ vcpu->arch.count_ctl;
 	s64 delta;
 	ktime_t expire, now;

arch/mips/kvm/mips.c

···
 static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
 			    const struct kvm_one_reg *reg)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	struct mips_fpu_struct *fpu = &vcpu->arch.fpu;
 	int ret;
 	s64 v;
···
 static int kvm_mips_set_reg(struct kvm_vcpu *vcpu,
 			    const struct kvm_one_reg *reg)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	struct mips_fpu_struct *fpu = &vcpu->arch.fpu;
 	s64 v;
 	s64 vs[2];
···
 int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
 {
 	return kvm_mips_pending_timer(vcpu) ||
-		kvm_read_c0_guest_cause(vcpu->arch.cop0) & C_TI;
+		kvm_read_c0_guest_cause(&vcpu->arch.cop0) & C_TI;
 }
 
 int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu)
···
 	kvm_debug("\thi: 0x%08lx\n", vcpu->arch.hi);
 	kvm_debug("\tlo: 0x%08lx\n", vcpu->arch.lo);
 
-	cop0 = vcpu->arch.cop0;
+	cop0 = &vcpu->arch.cop0;
 	kvm_debug("\tStatus: 0x%08x, Cause: 0x%08x\n",
 		  kvm_read_c0_guest_status(cop0),
 		  kvm_read_c0_guest_cause(cop0));
···
 
 	case EXCCODE_TLBS:
 		kvm_debug("TLB ST fault:  cause %#x, status %#x, PC: %p, BadVaddr: %#lx\n",
-			  cause, kvm_read_c0_guest_status(vcpu->arch.cop0), opc,
+			  cause, kvm_read_c0_guest_status(&vcpu->arch.cop0), opc,
 			  badvaddr);
 
 		++vcpu->stat.tlbmiss_st_exits;
···
 		kvm_get_badinstr(opc, vcpu, &inst);
 		kvm_err("Exception Code: %d, not yet handled, @ PC: %p, inst: 0x%08x  BadVaddr: %#lx Status: %#x\n",
 			exccode, opc, inst, badvaddr,
-			kvm_read_c0_guest_status(vcpu->arch.cop0));
+			kvm_read_c0_guest_status(&vcpu->arch.cop0));
 		kvm_arch_vcpu_dump_regs(vcpu);
 		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 		ret = RESUME_HOST;
···
 /* Enable FPU for guest and restore context */
 void kvm_own_fpu(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	unsigned int sr, cfg5;
 
 	preempt_disable();
···
 /* Enable MSA for guest and restore context */
 void kvm_own_msa(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	unsigned int sr, cfg5;
 
 	preempt_disable();

arch/mips/kvm/trace.h

···
 	    ),
 
 	    TP_fast_assign(
-			__entry->epc = kvm_read_c0_guest_epc(vcpu->arch.cop0);
+			__entry->epc = kvm_read_c0_guest_epc(&vcpu->arch.cop0);
 			__entry->pc = vcpu->arch.pc;
-			__entry->badvaddr = kvm_read_c0_guest_badvaddr(vcpu->arch.cop0);
-			__entry->status = kvm_read_c0_guest_status(vcpu->arch.cop0);
-			__entry->cause = kvm_read_c0_guest_cause(vcpu->arch.cop0);
+			__entry->badvaddr = kvm_read_c0_guest_badvaddr(&vcpu->arch.cop0);
+			__entry->status = kvm_read_c0_guest_status(&vcpu->arch.cop0);
+			__entry->cause = kvm_read_c0_guest_cause(&vcpu->arch.cop0);
 	    ),
 
 	    TP_printk("EPC: 0x%08lx PC: 0x%08lx Status: 0x%08x Cause: 0x%08x BadVAddr: 0x%08lx",

arch/mips/kvm/vz.c

···
  */
 static void kvm_vz_restore_timer(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	u32 cause, compare;
 
 	compare = kvm_read_sw_gc0_compare(cop0);
···
  */
 static void kvm_vz_save_timer(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	u32 gctl0, compare, cause;
 
 	gctl0 = read_c0_guestctl0();
···
 
 static void kvm_write_maari(struct kvm_vcpu *vcpu, unsigned long val)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 
 	val &= MIPS_MAARI_INDEX;
 	if (val == MIPS_MAARI_INDEX)
···
 					      u32 *opc, u32 cause,
 					      struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	enum emulation_result er = EMULATE_DONE;
 	u32 rt, rd, sel;
 	unsigned long curr_pc;
···
 			      const struct kvm_one_reg *reg,
 			      s64 *v)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	unsigned int idx;
 
 	switch (reg->id) {
···
 	case KVM_REG_MIPS_CP0_MAARI:
 		if (!cpu_guest_has_maar || cpu_guest_has_dyn_maar)
 			return -EINVAL;
-		*v = kvm_read_sw_gc0_maari(vcpu->arch.cop0);
+		*v = kvm_read_sw_gc0_maari(&vcpu->arch.cop0);
 		break;
 #ifdef CONFIG_64BIT
 	case KVM_REG_MIPS_CP0_XCONTEXT:
···
 			      const struct kvm_one_reg *reg,
 			      s64 v)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	unsigned int idx;
 	int ret = 0;
 	unsigned int cur, change;
···
 
 static int kvm_vz_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	bool migrated, all;
 
 	/*
···
 
 static int kvm_vz_vcpu_put(struct kvm_vcpu *vcpu, int cpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 
 	if (current->flags & PF_VCPU)
 		kvm_vz_vcpu_save_wired(vcpu);
···
 
 static int kvm_vz_vcpu_setup(struct kvm_vcpu *vcpu)
 {
-	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct mips_coproc *cop0 = &vcpu->arch.cop0;
 	unsigned long count_hz = 100*1000*1000; /* default to 100 MHz */
 
 	/*