x86/fpu: Move KVMs FPU swapping to FPU core

Swapping the host/guest FPU is directly fiddling with FPU internals which
requires 5 exports. The upcoming support of dynamically enabled states
would even need more.

Implement a swap function in the FPU core code and export that instead.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/20211015011539.076072399@linutronix.de

arch/x86/include/asm/fpu/api.h

@@ -12,6 +12,8 @@
 #define _ASM_X86_FPU_API_H
 #include <linux/bottom_half.h>
 
+#include <asm/fpu/types.h>
+
 /*
  * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
  * disables preemption so be careful if you intend to use it for long periods
@@ -108,4 +110,10 @@ extern int cpu_has_xfeatures(u64 xfeatures_mask, const char **feature_name);
 
 static inline void update_pasid(void) { }
 
+/* fpstate-related functions which are exported to KVM */
+extern void fpu_init_fpstate_user(struct fpu *fpu);
+
+/* KVM specific functions */
+extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
+
 #endif /* _ASM_X86_FPU_API_H */

arch/x86/include/asm/fpu/internal.h

@@ -74,14 +74,8 @@ static __always_inline __pure bool use_fxsr(void)
 	return static_cpu_has(X86_FEATURE_FXSR);
 }
 
-/*
- * fpstate handling functions:
- */
-
 extern union fpregs_state init_fpstate;
-
 extern void fpstate_init_user(union fpregs_state *state);
-extern void fpu_init_fpstate_user(struct fpu *fpu);
 
 #ifdef CONFIG_MATH_EMULATION
 extern void fpstate_init_soft(struct swregs_state *soft);
@@ -381,12 +375,7 @@ static inline int os_xrstor_safe(struct xregs_state *xstate, u64 mask)
 	return err;
 }
 
-extern void __restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask);
-
-static inline void restore_fpregs_from_fpstate(union fpregs_state *fpstate)
-{
-	__restore_fpregs_from_fpstate(fpstate, xfeatures_mask_fpstate());
-}
+extern void restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask);
 
 extern bool copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size);
 
@@ -467,7 +456,7 @@ static inline void fpregs_restore_userregs(void)
 		 */
 		mask = xfeatures_mask_restore_user() |
 			xfeatures_mask_supervisor();
-		__restore_fpregs_from_fpstate(&fpu->state, mask);
+		restore_fpregs_from_fpstate(&fpu->state, mask);
 
 		fpregs_activate(fpu);
 		fpu->last_cpu = cpu;

arch/x86/kernel/fpu/core.c

@@ -124,9 +124,8 @@ void save_fpregs_to_fpstate(struct fpu *fpu)
 	asm volatile("fnsave %[fp]; fwait" : [fp] "=m" (fpu->state.fsave));
 	frstor(&fpu->state.fsave);
 }
-EXPORT_SYMBOL(save_fpregs_to_fpstate);
 
-void __restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
+void restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
 {
 	/*
 	 * AMD K7/K8 and later CPUs up to Zen don't save/restore
@@ -151,7 +150,31 @@ void __restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
 			frstor(&fpstate->fsave);
 	}
 }
-EXPORT_SYMBOL_GPL(__restore_fpregs_from_fpstate);
+
+#if IS_ENABLED(CONFIG_KVM)
+void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
+{
+	fpregs_lock();
+
+	if (save) {
+		if (test_thread_flag(TIF_NEED_FPU_LOAD)) {
+			memcpy(&save->state, &current->thread.fpu.state,
+			       fpu_kernel_xstate_size);
+		} else {
+			save_fpregs_to_fpstate(save);
+		}
+	}
+
+	if (rstor) {
+		restore_mask &= xfeatures_mask_fpstate();
+		restore_fpregs_from_fpstate(&rstor->state, restore_mask);
+	}
+
+	fpregs_mark_activate();
+	fpregs_unlock();
+}
+EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
+#endif
 
 void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 {
@@ -457,7 +480,6 @@ void fpregs_mark_activate(void)
 	fpu->last_cpu = smp_processor_id();
 	clear_thread_flag(TIF_NEED_FPU_LOAD);
 }
-EXPORT_SYMBOL_GPL(fpregs_mark_activate);
 
 /*
  * x87 math exception handling:

arch/x86/kernel/fpu/init.c

@@ -136,7 +136,6 @@ static void __init fpu__init_system_generic(void)
  * components into a single, continuous memory block:
  */
 unsigned int fpu_kernel_xstate_size __ro_after_init;
-EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
 
 /* Get alignment of the TYPE. */
 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)

arch/x86/kernel/fpu/xstate.c

@@ -65,7 +65,6 @@ static short xsave_cpuid_features[] __initdata = {
  * XSAVE buffer, both supervisor and user xstates.
  */
 u64 xfeatures_mask_all __ro_after_init;
-EXPORT_SYMBOL_GPL(xfeatures_mask_all);
 
 static unsigned int xstate_offsets[XFEATURE_MAX] __ro_after_init =
 	{ [ 0 ... XFEATURE_MAX - 1] = -1};

arch/x86/kvm/x86.c

@@ -68,7 +68,9 @@
 #include <asm/mce.h>
 #include <asm/pkru.h>
 #include <linux/kernel_stat.h>
-#include <asm/fpu/internal.h> /* Ugh! */
+#include <asm/fpu/api.h>
+#include <asm/fpu/xcr.h>
+#include <asm/fpu/xstate.h>
 #include <asm/pvclock.h>
 #include <asm/div64.h>
 #include <asm/irq_remapping.h>
@@ -9913,58 +9915,27 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
-static void kvm_save_current_fpu(struct fpu *fpu)
-{
-	/*
-	 * If the target FPU state is not resident in the CPU registers, just
-	 * memcpy() from current, else save CPU state directly to the target.
-	 */
-	if (test_thread_flag(TIF_NEED_FPU_LOAD))
-		memcpy(&fpu->state, &current->thread.fpu.state,
-		       fpu_kernel_xstate_size);
-	else
-		save_fpregs_to_fpstate(fpu);
-}
-
 /* Swap (qemu) user FPU context for the guest FPU context. */
 static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
 {
-	fpregs_lock();
-
-	kvm_save_current_fpu(vcpu->arch.user_fpu);
-
 	/*
-	 * Guests with protected state can't have it set by the hypervisor,
-	 * so skip trying to set it.
+	 * Guests with protected state have guest_fpu == NULL which makes
+	 * the swap only save the host state. Exclude PKRU from restore as
+	 * it is restored separately in kvm_x86_ops.run().
 	 */
-	if (vcpu->arch.guest_fpu)
-		/* PKRU is separately restored in kvm_x86_ops.run. */
-		__restore_fpregs_from_fpstate(&vcpu->arch.guest_fpu->state,
-					~XFEATURE_MASK_PKRU);
-
-	fpregs_mark_activate();
-	fpregs_unlock();
-
+	fpu_swap_kvm_fpu(vcpu->arch.user_fpu, vcpu->arch.guest_fpu,
+			 ~XFEATURE_MASK_PKRU);
 	trace_kvm_fpu(1);
 }
 
 /* When vcpu_run ends, restore user space FPU context. */
 static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 {
-	fpregs_lock();
-
 	/*
-	 * Guests with protected state can't have it read by the hypervisor,
-	 * so skip trying to save it.
+	 * Guests with protected state have guest_fpu == NULL which makes
+	 * swap only restore the host state.
 	 */
-	if (vcpu->arch.guest_fpu)
-		kvm_save_current_fpu(vcpu->arch.guest_fpu);
-
-	restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state);
-
-	fpregs_mark_activate();
-	fpregs_unlock();
-
+	fpu_swap_kvm_fpu(vcpu->arch.guest_fpu, vcpu->arch.user_fpu, ~0ULL);
 	++vcpu->stat.fpu_reload;
 	trace_kvm_fpu(0);
 }

arch/x86/mm/extable.c

@@ -47,7 +47,7 @@ static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 	WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
 		  (void *)instruction_pointer(regs));
 
-	__restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
+	restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
 	return true;
 }