From 2a1fc7dc36260fbe74b6ca29dc6d9088194a2115 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 12 Jul 2024 07:48:41 -0700 Subject: [PATCH] KVM: x86: Suppress MMIO that is triggered during task switch emulation Explicitly suppress userspace emulated MMIO exits that are triggered when emulating a task switch as KVM doesn't support userspace MMIO during complex (multi-step) emulation. Silently ignoring the exit request can result in the WARN_ON_ONCE(vcpu->mmio_needed) firing if KVM exits to userspace for some other reason prior to purging mmio_needed. See commit 0dc902267cb3 ("KVM: x86: Suppress pending MMIO write exits if emulator detects exception") for more details on KVM's limitations with respect to emulated MMIO during complex emulator flows. Reported-by: syzbot+2fb9f8ed752c01bc9a3f@syzkaller.appspotmail.com Signed-off-by: Sean Christopherson Message-ID: <20240712144841.1230591-1-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index caf528bb775b..6c07f7ff0eff 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11800,7 +11800,13 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index, ret = emulator_task_switch(ctxt, tss_selector, idt_index, reason, has_error_code, error_code); - if (ret) { + + /* + * Report an error userspace if MMIO is needed, as KVM doesn't support + * MMIO during a task switch (or any other complex operation). + */ + if (ret || vcpu->mmio_needed) { + vcpu->mmio_needed = false; vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION; vcpu->run->internal.ndata = 0; -- 2.50.1