KVM: MIPS: Use CP0_BadInstr[P] for emulation

When exiting from the guest, store the values of the CP0_BadInstr and
CP0_BadInstrP registers if they exist, which contain the encodings of
the instructions which caused the last synchronous exception.

When the instruction is needed for emulation, kvm_get_badinstr() and
kvm_get_badinstrp() are used instead of calling kvm_get_inst() directly,
to decide whether to read the saved CP0_BadInstr/CP0_BadInstrP registers
(if they exist), or read the instruction from memory (if not).

The use of these registers should be more robust than using
kvm_get_inst(), as it actually gives the instruction encoding seen by
the hardware rather than relying on user accessors after the fact, which
can be fooled by incoherent icache or a racing code modification. It
will also work with VZ, where the guest virtual memory isn't directly
accessible by the host with user accessors.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index f296ebeda9e3..17c5e53ef3fa 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -280,6 +280,8 @@ struct kvm_vcpu_arch {
 	unsigned long host_cp0_badvaddr;
 	unsigned long host_cp0_epc;
 	u32 host_cp0_cause;
+	u32 host_cp0_badinstr;
+	u32 host_cp0_badinstrp;
 
 	/* GPRS */
 	unsigned long gprs[32];
@@ -641,6 +643,8 @@ void kvm_trap_emul_invalidate_gva(struct kvm_vcpu *vcpu, unsigned long addr,
 /* Emulation */
 int kvm_get_inst(u32 *opc, struct kvm_vcpu *vcpu, u32 *out);
 enum emulation_result update_pc(struct kvm_vcpu *vcpu, u32 cause);
+int kvm_get_badinstr(u32 *opc, struct kvm_vcpu *vcpu, u32 *out);
+int kvm_get_badinstrp(u32 *opc, struct kvm_vcpu *vcpu, u32 *out);
 
 /**
  * kvm_is_ifetch_fault() - Find whether a TLBL exception is due to ifetch fault.