From: Sean Christopherson seanjc@google.com
commit d07898eaf39909806128caccb6ebd922ee3edd69 upstream.
Replace a WARN with a comment to call out that userspace can modify RCX during an exit to userspace to handle string I/O. KVM doesn't actually support changing the rep count during an exit, i.e. the scenario can be ignored, but the WARN needs to go as it's trivial to trigger from userspace.
Cc: stable@vger.kernel.org Fixes: 3b27de271839 ("KVM: x86: split the two parts of emulator_pio_in") Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20211025201311.1881846-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/x86.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7021,7 +7021,13 @@ static int emulator_pio_in(struct kvm_vc unsigned short port, void *val, unsigned int count) { if (vcpu->arch.pio.count) { - /* Complete previous iteration. */ + /* + * Complete a previous iteration that required userspace I/O. + * Note, @count isn't guaranteed to match pio.count as userspace + * can modify ECX before rerunning the vCPU. Ignore any such + * shenanigans as KVM doesn't support modifying the rep count, + * and the emulator ensures @count doesn't overflow the buffer. + */ } else { int r = __emulator_pio_in(vcpu, size, port, count); if (!r) @@ -7030,7 +7036,6 @@ static int emulator_pio_in(struct kvm_vc /* Results already available, fall through. */ }
- WARN_ON(count != vcpu->arch.pio.count); complete_emulator_pio_in(vcpu, val); return 1; }