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Subject[PATCH v2 3/8] KVM: x86: drop PIO from unregistered devices
Date
KVM protects the device list with SRCU, and therefore different calls
to kvm_io_bus_read()/kvm_io_bus_write() can very well see different
incarnations of kvm->buses. If userspace unregisters a device while
vCPUs are running there is no well-defined result. This patch applies
a safe fallback by returning early from emulator_pio_in_out(). This
corresponds to returning zeroes from IN, and dropping the writes on
the floor for OUT.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/x86.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 524a96d26399..5a56d39bd81f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7593,8 +7593,19 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, port, size, data);
else
r = kvm_io_bus_write(vcpu, KVM_PIO_BUS, port, size, data);
- if (r)
- goto userspace_io;
+
+ if (r) {
+ if (i == 0)
+ goto userspace_io;
+
+ /*
+ * Userspace must have unregistered the device while PIO
+ * was running. Drop writes / read as 0 (the buffer
+ * was zeroed in __emulator_pio_in).
+ */
+ break;
+ }
+
data += size;
}
return 1;
@@ -7606,7 +7617,6 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
vcpu->run->io.data_offset = KVM_PIO_PAGE_OFFSET * PAGE_SIZE;
vcpu->run->io.count = count;
vcpu->run->io.port = port;
-
return 0;
}

--
2.31.1

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