st  enabled at (30570): [<ffffffffb4247a64>] fpu_swap_kvm_fpstate+0x44/0x210
 softirqs last disabled at (30568): [<ffffffffb4247a64>] fpu_swap_kvm_fpstate+0x44/0x210
 CPU: 298 UID: 0 PID: 32611 Comm: qemu Tainted: G     U              6.16.0-smp--e6c618b51cfe-sleep #782 NONE
 Tainted: [U]=USER
 Hardware name: Google Astoria-Turin/astoria, BIOS 0.20241223.2-0 01/17/2025
 Call Trace:
  <TASK>
  dump_stack_lvl+0x7d/0xb0
  __might_resched+0x271/0x290
  __might_fault+0x28/0x80
  kvm_vcpu_read_guest_page+0x8d/0xc0 [kvm]
  kvm_fetch_guest_virt+0x92/0xc0 [kvm]
  __do_insn_fetch_bytes+0xf3/0x1e0 [kvm]
  x86_decode_insn+0xd1/0x1010 [kvm]
  x86_emulate_instruction+0x105/0x810 [kvm]
  __svm_skip_emulated_instruction+0xc4/0x140 [kvm_amd]
  handle_fastpath_invd+0xc4/0x1a0 [kvm]
  vcpu_run+0x11a1/0x1db0 [kvm]
  kvm_arch_vcpu_ioctl_run+0x5cc/0x730 [kvm]
  kvm_vcpu_ioctl+0x578/0x6a0 [kvm]
  __se_sys_ioctl+0x6d/0xb0
  do_syscall_64+0x8a/0x2c0
  entry_SYSCALL_64_after_hwframe+0x4b/0x53
 RIP: 0033:0x7f479d57a94b
  </TASK>

Note, this is essentially a reapply of commit 5c30e8101e8d ("KVM: SVM:
Skip WRMSR fastpath on VM-Exit if next RIP isn't valid"), but with
different justification (KVM now grabs SRCU when skipping the instruction
for other reasons).

Fixes: b439eb8ab578 ("Revert "KVM: SVM: Skip WRMSR fastpath on VM-Exit if next RIP isn't valid"")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250805190526.1453366-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d9931c6c4bc6..829d9d46718d 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4181,13 +4181,21 @@ static int svm_vcpu_pre_run(struct kvm_vcpu *vcpu)
 static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	struct vmcb_control_area *control = &svm->vmcb->control;
+
+	/*
+	 * Next RIP must be provided as IRQs are disabled, and accessing guest
+	 * memory to decode the instruction might fault, i.e. might sleep.
+	 */
+	if (!nrips || !control->next_rip)
+		return EXIT_FASTPATH_NONE;
 
 	if (is_guest_mode(vcpu))
 		return EXIT_FASTPATH_NONE;
 
-	switch (svm->vmcb->control.exit_code) {
+	switch (control->exit_code) {
 	case SVM_EXIT_MSR:
-		if (!svm->vmcb->control.exit_info_1)
+		if (!control->exit_info_1)
 			break;
 		return handle_fastpath_set_msr_irqoff(vcpu);
 	case SVM_EXIT_HLT:FAILED: patch "[PATCH] KVM: SVM: Skip fastpath emulation on VM-Exit if next RIP" failed to apply to 6.6-stable tree<gregkh@linuxfoundation.org> undefinedseanjc@google.com undefined undefined«7ƒŽ+