x86/fpu: Replace KVMs xstate component clearing

In order to prepare for the support of dynamically enabled FPU features,
move the clearing of xstate components to the FPU core code.

No functional change.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Cc: kvm@vger.kernel.org
Link: https://lkml.kernel.org/r/20211013145322.399567049@linutronix.de

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

@@ -132,6 +132,7 @@ DECLARE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
 /* fpstate-related functions which are exported to KVM */
 extern void fpu_init_fpstate_user(struct fpu *fpu);
+extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
 
 /* KVM specific functions */
 extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);

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

@@ -128,7 +128,6 @@ extern u64 xstate_fx_sw_bytes[USER_XSTATE_FX_SW_WORDS];
 extern void __init update_regset_xstate_info(unsigned int size,
 					     u64 xstate_mask);
 
-void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
 int xfeature_size(int xfeature_nr);
 int copy_uabi_from_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf);
 int copy_sigframe_from_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf);

arch/x86/kernel/fpu/xstate.c

@@ -908,7 +908,6 @@ void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr)
 
 	return __raw_xsave_addr(xsave, xfeature_nr);
 }
-EXPORT_SYMBOL_GPL(get_xsave_addr);
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
 
@@ -1257,6 +1256,17 @@ void xrstors(struct xregs_state *xstate, u64 mask)
 	WARN_ON_ONCE(err);
 }
 
+#if IS_ENABLED(CONFIG_KVM)
+void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature)
+{
+	void *addr = get_xsave_addr(&fps->regs.xsave, xfeature);
+
+	if (addr)
+		memset(addr, 0, xstate_sizes[xfeature]);
+}
+EXPORT_SYMBOL_GPL(fpstate_clear_xstate_component);
+#endif
+
 #ifdef CONFIG_PROC_PID_ARCH_STATUS
 /*
  * Report the amount of time elapsed in millisecond since last AVX512

arch/x86/kernel/fpu/xstate.h

@@ -21,6 +21,8 @@ extern void __copy_xstate_to_uabi_buf(struct membuf to, struct xregs_state *xsav
 extern void fpu__init_cpu_xstate(void);
 extern void fpu__init_system_xstate(void);
 
+extern void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
+
 /* XSAVE/XRSTOR wrapper functions */
 
 #ifdef CONFIG_X86_64

arch/x86/kvm/x86.c

@@ -10705,7 +10705,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vcpu->arch.apf.halted = false;
 
 	if (vcpu->arch.guest_fpu && kvm_mpx_supported()) {
-		void *mpx_state_buffer;
+		struct fpstate *fpstate = vcpu->arch.guest_fpu->fpstate;
 
 		/*
 		 * To avoid have the INIT path from kvm_apic_has_events() that be
@@ -10713,14 +10713,10 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 		 */
 		if (init_event)
 			kvm_put_guest_fpu(vcpu);
-		mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu->state.xsave,
-					XFEATURE_BNDREGS);
-		if (mpx_state_buffer)
-			memset(mpx_state_buffer, 0, sizeof(struct mpx_bndreg_state));
-		mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu->state.xsave,
-					XFEATURE_BNDCSR);
-		if (mpx_state_buffer)
-			memset(mpx_state_buffer, 0, sizeof(struct mpx_bndcsr));
+
+		fpstate_clear_xstate_component(fpstate, XFEATURE_BNDREGS);
+		fpstate_clear_xstate_component(fpstate, XFEATURE_BNDCSR);
+
 		if (init_event)
 			kvm_load_guest_fpu(vcpu);
 	}