MIPS: KVM: Handle MSA Disabled exceptions from guest

commit 98119ad53376885819d93dfb8737b6a9a61ca0ba upstream.

Guest user mode can generate a guest MSA Disabled exception on an MSA
capable core by simply trying to execute an MSA instruction. Since this
exception is unknown to KVM it will be passed on to the guest kernel.
However guest Linux kernels prior to v3.15 do not set up an exception
handler for the MSA Disabled exception as they don't support any MSA
capable cores. This results in a guest OS panic.

Since an older processor ID may be being emulated, and MSA support is
not advertised to the guest, the correct behaviour is to generate a
Reserved Instruction exception in the guest kernel so it can send the
guest process an illegal instruction signal (SIGILL), as would happen
with a non-MSA-capable core.

Fix this as minimally as reasonably possible by preventing
kvm_mips_check_privilege() from relaying MSA Disabled exceptions from
guest user mode to the guest kernel, and handling the MSA Disabled
exception by emulating a Reserved Instruction exception in the guest,
via a new handle_msa_disabled() KVM callback.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
[ luis: backported to 3.16: files renamed:
  - arch/mips/kvm/emulate.c -> arch/mips/kvm/kvm_mips_emul.c
  - arch/mips/kvm/mips.c -> arch/mips/kvm/kvm_mips.c]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index b0aa95565752a8d79212ecfd0bc56be0bacd2e42..5a8defbad431a20ab4cac2a97b89278914141019 100644 (file)
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -326,6 +326,7 @@ enum mips_mmu_types {
 #define T_TRAP                 13      /* Trap instruction */
 #define T_VCEI                 14      /* Virtual coherency exception */
 #define T_FPE                  15      /* Floating point exception */
+#define T_MSADIS               21      /* MSA disabled exception */
 #define T_WATCH                        23      /* Watch address reference */
 #define T_VCED                 31      /* Virtual coherency data */
 
@@ -578,6 +579,7 @@ struct kvm_mips_callbacks {
        int (*handle_syscall)(struct kvm_vcpu *vcpu);
        int (*handle_res_inst)(struct kvm_vcpu *vcpu);
        int (*handle_break)(struct kvm_vcpu *vcpu);
+       int (*handle_msa_disabled)(struct kvm_vcpu *vcpu);
        int (*vm_init)(struct kvm *kvm);
        int (*vcpu_init)(struct kvm_vcpu *vcpu);
        int (*vcpu_setup)(struct kvm_vcpu *vcpu);

diff --git a/arch/mips/kvm/kvm_mips.c b/arch/mips/kvm/kvm_mips.c
index d84f96e51349860f74ae808de72356a3710912ad..59298b97ac39b87177fffe5b1f55a16cec2e965e 100644 (file)
--- a/arch/mips/kvm/kvm_mips.c
+++ b/arch/mips/kvm/kvm_mips.c
@@ -1156,6 +1156,10 @@ int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
                ret = kvm_mips_callbacks->handle_break(vcpu);
                break;
 
+       case T_MSADIS:
+               ret = kvm_mips_callbacks->handle_msa_disabled(vcpu);
+               break;
+
        default:
                kvm_err
                    ("Exception Code: %d, not yet handled, @ PC: %p, inst: 0x%08x  BadVaddr: %#lx Status: %#lx\n",

diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index 8d484009008283e9afdd0da7344c99cf4b8ec8e6..2071472bc3c406766dd267b7e4ccb2ba3df3189e 100644 (file)
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -2204,6 +2204,7 @@ kvm_mips_check_privilege(unsigned long cause, uint32_t *opc,
                case T_SYSCALL:
                case T_BREAK:
                case T_RES_INST:
+               case T_MSADIS:
                        break;
 
                case T_COP_UNUSABLE:

diff --git a/arch/mips/kvm/kvm_trap_emul.c b/arch/mips/kvm/kvm_trap_emul.c
index 693f952b2fbb532d93e76c648172dc6211c8e201..0c521c3565534e95e012629db36e372e8e490ca2 100644 (file)
--- a/arch/mips/kvm/kvm_trap_emul.c
+++ b/arch/mips/kvm/kvm_trap_emul.c
@@ -333,6 +333,33 @@ static int kvm_trap_emul_handle_break(struct kvm_vcpu *vcpu)
        return ret;
 }
 
+static int kvm_trap_emul_handle_msa_disabled(struct kvm_vcpu *vcpu)
+{
+       struct kvm_run *run = vcpu->run;
+       uint32_t __user *opc = (uint32_t __user *) vcpu->arch.pc;
+       unsigned long cause = vcpu->arch.host_cp0_cause;
+       enum emulation_result er = EMULATE_DONE;
+       int ret = RESUME_GUEST;
+
+       /* No MSA supported in guest, guest reserved instruction exception */
+       er = kvm_mips_emulate_ri_exc(cause, opc, run, vcpu);
+
+       switch (er) {
+       case EMULATE_DONE:
+               ret = RESUME_GUEST;
+               break;
+
+       case EMULATE_FAIL:
+               run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+               ret = RESUME_HOST;
+               break;
+
+       default:
+               BUG();
+       }
+       return ret;
+}
+
 static int kvm_trap_emul_vm_init(struct kvm *kvm)
 {
        return 0;
@@ -472,6 +499,7 @@ static struct kvm_mips_callbacks kvm_trap_emul_callbacks = {
        .handle_syscall = kvm_trap_emul_handle_syscall,
        .handle_res_inst = kvm_trap_emul_handle_res_inst,
        .handle_break = kvm_trap_emul_handle_break,
+       .handle_msa_disabled = kvm_trap_emul_handle_msa_disabled,
 
        .vm_init = kvm_trap_emul_vm_init,
        .vcpu_init = kvm_trap_emul_vcpu_init,