MIPS: KVM: Add base guest FPU support

Add base code for supporting FPU in MIPS KVM guests. The FPU cannot yet
be enabled in the guest, we're just laying the groundwork.

Whether the guest's FPU context is loaded is stored in a bit in the
fpu_inuse vcpu member. This allows the FPU to be disabled when the guest
disables it, but keeping the FPU context loaded so it doesn't have to be
reloaded if the guest re-enables it.

An fpu_enabled vcpu member stores whether userland has enabled the FPU
capability (which will be wired up in a later patch).

New assembly code is added for saving and restoring the FPU context, and
for saving/clearing and restoring FCSR (which can itself cause an FP
exception depending on the value). The FCSR is restored before returning
to the guest if the FPU is already enabled, and a die notifier is
registered to catch the possible FP exception and step over the ctc1
instruction.

The helper function kvm_lose_fpu() is added to save FPU context and
disable the FPU, which is used when saving hardware state before a
context switch or KVM exit (the vcpu_get_regs() callback).

The helper function kvm_own_fpu() is added to enable the FPU and restore
the FPU context if it isn't already loaded, which will be used in a
later patch when the guest attempts to use the FPU for the first time
and triggers a co-processor unusable exception.

The helper function kvm_drop_fpu() is added to discard the FPU context
and disable the FPU, which will be used in a later patch when the FPU
state will become architecturally UNPREDICTABLE (change of FR mode) to
force a reload of [stale] context in the new FR mode.

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

1 files changed, 27 insertions, 0 deletions

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index fb79d67..866edf3 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -357,6 +357,8 @@ struct kvm_mips_tlb {
 	long tlb_lo1;
 };
 
+#define KVM_MIPS_FPU_FPU	0x1
+
 #define KVM_MIPS_GUEST_TLB_SIZE	64
 struct kvm_vcpu_arch {
 	void *host_ebase, *guest_ebase;
@@ -378,6 +380,8 @@ struct kvm_vcpu_arch {
 
 	/* FPU State */
 	struct mips_fpu_struct fpu;
+	/* Which FPU state is loaded (KVM_MIPS_FPU_*) */
+	unsigned int fpu_inuse;
 
 	/* COP0 State */
 	struct mips_coproc *cop0;
@@ -424,6 +428,8 @@ struct kvm_vcpu_arch {
 
 	/* WAIT executed */
 	int wait;
+
+	u8 fpu_enabled;
 };
 
 
@@ -554,6 +560,19 @@ static inline void _kvm_atomic_change_c0_guest_reg(unsigned long *reg,
 	kvm_set_c0_guest_ebase(cop0, ((val) & (change)));		\
 }
 
+/* Helpers */
+
+static inline bool kvm_mips_guest_can_have_fpu(struct kvm_vcpu_arch *vcpu)
+{
+	return (!__builtin_constant_p(cpu_has_fpu) || cpu_has_fpu) &&
+		vcpu->fpu_enabled;
+}
+
+static inline bool kvm_mips_guest_has_fpu(struct kvm_vcpu_arch *vcpu)
+{
+	return kvm_mips_guest_can_have_fpu(vcpu) &&
+		kvm_read_c0_guest_config1(vcpu->cop0) & MIPS_CONF1_FP;
+}
 
 struct kvm_mips_callbacks {
 	int (*handle_cop_unusable)(struct kvm_vcpu *vcpu);
@@ -597,6 +616,14 @@ int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu);
 /* Trampoline ASM routine to start running in "Guest" context */
 extern int __kvm_mips_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu);
 
+/* FPU context management */
+void __kvm_save_fpu(struct kvm_vcpu_arch *vcpu);
+void __kvm_restore_fpu(struct kvm_vcpu_arch *vcpu);
+void __kvm_restore_fcsr(struct kvm_vcpu_arch *vcpu);
+void kvm_own_fpu(struct kvm_vcpu *vcpu);
+void kvm_drop_fpu(struct kvm_vcpu *vcpu);
+void kvm_lose_fpu(struct kvm_vcpu *vcpu);
+
 /* TLB handling */
 uint32_t kvm_get_kernel_asid(struct kvm_vcpu *vcpu);