| Message ID | 20170314000515.26573-1-james.hogan@imgtec.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Mar 14, 2017 at 12:05:15AM +0000, James Hogan wrote: > Host kernels with preemption enabled will emit the following preemption > warning when the guest FPU is used: > > BUG: using smp_processor_id() in preemptible [00000000] code: qemu-system-mip/1495 > caller is kvm_mips_emulate_CP0+0xa48/0xea0 [kvm] > ... > Call Trace: > [<ffffffff81122d50>] show_stack+0x88/0xa8 > [<ffffffff814307ac>] dump_stack+0x9c/0xd0 > [<ffffffff81459f24>] check_preemption_disabled+0x124/0x130 > [<ffffffffc000e908>] kvm_mips_emulate_CP0+0xa48/0xea0 [kvm] > [<ffffffffc000f9f0>] kvm_mips_emulate_inst+0x190/0x268 [kvm] > [<ffffffffc0016220>] kvm_trap_emul_handle_cop_unusable+0x48/0x160 [kvm] > [<ffffffffc000c120>] kvm_mips_handle_exit+0x520/0x7e0 [kvm] > > This is due to the use of current_cpu_data.fpu_id from a preemptible > context to read the MIPS_FPIR_F64 bit. We don't currently support > asymmetric FPU capabilities with KVM, so just use boot_cpu_data instead > to silence the warning. > > Fixes: 6cdc65e31d4f ("MIPS: KVM: Emulate FPU bits in COP0 interface") > 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 > Cc: <stable@vger.kernel.org> # 4.1.x- Acked-by: Ralf Baechle <ralf@linux-mips.org> James, we've fixed too many of these warnings over the past years, we should look for a solution to kill this whole class of bugs. Ralf
diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c index d40cfaad4529..9bc55619252a 100644 --- a/arch/mips/kvm/emulate.c +++ b/arch/mips/kvm/emulate.c @@ -1279,7 +1279,7 @@ enum emulation_result kvm_mips_emulate_CP0(union mips_instruction inst, * Also don't allow FR to be set if host doesn't * support it. */ - if (!(current_cpu_data.fpu_id & MIPS_FPIR_F64)) + if (!(boot_cpu_data.fpu_id & MIPS_FPIR_F64)) val &= ~ST0_FR;
Host kernels with preemption enabled will emit the following preemption warning when the guest FPU is used: BUG: using smp_processor_id() in preemptible [00000000] code: qemu-system-mip/1495 caller is kvm_mips_emulate_CP0+0xa48/0xea0 [kvm] ... Call Trace: [<ffffffff81122d50>] show_stack+0x88/0xa8 [<ffffffff814307ac>] dump_stack+0x9c/0xd0 [<ffffffff81459f24>] check_preemption_disabled+0x124/0x130 [<ffffffffc000e908>] kvm_mips_emulate_CP0+0xa48/0xea0 [kvm] [<ffffffffc000f9f0>] kvm_mips_emulate_inst+0x190/0x268 [kvm] [<ffffffffc0016220>] kvm_trap_emul_handle_cop_unusable+0x48/0x160 [kvm] [<ffffffffc000c120>] kvm_mips_handle_exit+0x520/0x7e0 [kvm] This is due to the use of current_cpu_data.fpu_id from a preemptible context to read the MIPS_FPIR_F64 bit. We don't currently support asymmetric FPU capabilities with KVM, so just use boot_cpu_data instead to silence the warning. Fixes: 6cdc65e31d4f ("MIPS: KVM: Emulate FPU bits in COP0 interface") 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 Cc: <stable@vger.kernel.org> # 4.1.x- --- arch/mips/kvm/emulate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)