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@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
---
arch/mips/include/asm/kvm_host.h | 4 +++-
arch/mips/kvm/emulate.c | 48 ++++++++++++++++++++++++++++++---
arch/mips/kvm/entry.c | 14 ++++++++++-
arch/mips/kvm/mips.c | 2 +-
4 files changed, 64 insertions(+), 4 deletions(-)
diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index b0936a4d931a..ac9d41900597 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];
@@ -638,6 +640,8 @@ 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.
diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index b906fc0589f3..b295a4a1496f 100644
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -54,7 +54,7 @@ static int kvm_compute_return_epc(struct kvm_vcpu *vcpu, unsigned long instpc,
}
/* Read the instruction */
- err = kvm_get_inst((u32 *)epc, vcpu, &insn.word);
+ err = kvm_get_badinstrp((u32 *)epc, vcpu, &insn.word);
if (err)
return err;
@@ -259,6 +259,48 @@ enum emulation_result update_pc(struct kvm_vcpu *vcpu, u32 cause)
}
/**
+ * kvm_get_badinstr() - Get bad instruction encoding.
+ * @opc: Guest pointer to faulting instruction.
+ * @vcpu: KVM VCPU information.
+ *
+ * Gets the instruction encoding of the faulting instruction, using the saved
+ * BadInstr register value if it exists, otherwise falling back to reading guest
+ * memory at @opc.
+ *
+ * Returns: The instruction encoding of the faulting instruction.
+ */
+int kvm_get_badinstr(u32 *opc, struct kvm_vcpu *vcpu, u32 *out)
+{
+ if (cpu_has_badinstr) {
+ *out = vcpu->arch.host_cp0_badinstr;
+ return 0;
+ } else {
+ return kvm_get_inst(opc, vcpu, out);
+ }
+}
+
+/**
+ * kvm_get_badinstrp() - Get bad prior instruction encoding.
+ * @opc: Guest pointer to prior faulting instruction.
+ * @vcpu: KVM VCPU information.
+ *
+ * Gets the instruction encoding of the prior faulting instruction (the branch
+ * containing the delay slot which faulted), using the saved BadInstrP register
+ * value if it exists, otherwise falling back to reading guest memory at @opc.
+ *
+ * Returns: The instruction encoding of the prior faulting instruction.
+ */
+int kvm_get_badinstrp(u32 *opc, struct kvm_vcpu *vcpu, u32 *out)
+{
+ if (cpu_has_badinstrp) {
+ *out = vcpu->arch.host_cp0_badinstrp;
+ return 0;
+ } else {
+ return kvm_get_inst(opc, vcpu, out);
+ }
+}
+
+/**
* kvm_mips_count_disabled() - Find whether the CP0_Count timer is disabled.
* @vcpu: Virtual CPU.
*
@@ -1839,7 +1881,7 @@ enum emulation_result kvm_mips_emulate_inst(u32 cause, u32 *opc,
/* Fetch the instruction. */
if (cause & CAUSEF_BD)
opc += 1;
- err = kvm_get_inst(opc, vcpu, &inst.word);
+ err = kvm_get_badinstr(opc, vcpu, &inst.word);
if (err)
return EMULATE_FAIL;
@@ -2434,7 +2476,7 @@ enum emulation_result kvm_mips_handle_ri(u32 cause, u32 *opc,
/* Fetch the instruction. */
if (cause & CAUSEF_BD)
opc += 1;
- err = kvm_get_inst(opc, vcpu, &inst.word);
+ err = kvm_get_badinstr(opc, vcpu, &inst.word);
if (err) {
kvm_err("%s: Cannot get inst @ %p (%d)\n", __func__, opc, err);
return EMULATE_FAIL;
diff --git a/arch/mips/kvm/entry.c b/arch/mips/kvm/entry.c
index 1ae33e0e675c..c5b254c4d0da 100644
--- a/arch/mips/kvm/entry.c
+++ b/arch/mips/kvm/entry.c
@@ -53,6 +53,8 @@
/* Some CP0 registers */
#define C0_HWRENA 7, 0
#define C0_BADVADDR 8, 0
+#define C0_BADINSTR 8, 1
+#define C0_BADINSTRP 8, 2
#define C0_ENTRYHI 10, 0
#define C0_STATUS 12, 0
#define C0_CAUSE 13, 0
@@ -579,6 +581,18 @@ void *kvm_mips_build_exit(void *addr)
uasm_i_mfc0(&p, K0, C0_CAUSE);
uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch, host_cp0_cause), K1);
+ if (cpu_has_badinstr) {
+ uasm_i_mfc0(&p, K0, C0_BADINSTR);
+ uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch,
+ host_cp0_badinstr), K1);
+ }
+
+ if (cpu_has_badinstrp) {
+ uasm_i_mfc0(&p, K0, C0_BADINSTRP);
+ uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch,
+ host_cp0_badinstrp), K1);
+ }
+
/* Now restore the host state just enough to run the handlers */
/* Switch EBASE to the one used by Linux */
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 69775fb9c408..4dc6cf2b7c50 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -1476,7 +1476,7 @@ int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
if (cause & CAUSEF_BD)
opc += 1;
inst = 0;
- kvm_get_inst(opc, vcpu, &inst);
+ kvm_get_badinstr(opc, vcpu, &inst);
kvm_err("Exception Code: %d, not yet handled, @ PC: %p, inst: 0x%08x BadVaddr: %#lx Status: %#lx\n",
exccode, opc, inst, badvaddr,
kvm_read_c0_guest_status(vcpu->arch.cop0));
--
git-series 0.8.10
