x86/kvm: Convert FPU handling to a single swap buffer

For the upcoming AMX support it's necessary to do a proper integration with
KVM. Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Convert the KVM FPU code over to this new scheme.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211022185313.019454292@linutronix.de

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

@@ -140,8 +140,8 @@ extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
 extern int fpu_swap_kvm_fpstate(struct fpu_guest *gfpu, bool enter_guest);
 extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
 
-extern int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0, u32 *pkru);
-extern void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf, unsigned int size, u32 pkru);
+extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
+extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
 
 static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
 {

arch/x86/include/asm/kvm_host.h

@@ -691,11 +691,10 @@ struct kvm_vcpu_arch {
 	 *
 	 * Note that while the PKRU state lives inside the fpu registers,
 	 * it is switched out separately at VMENTER and VMEXIT time. The
-	 * "guest_fpu" state here contains the guest FPU context, with the
+	 * "guest_fpstate" state here contains the guest FPU context, with the
 	 * host PRKU bits.
 	 */
-	struct fpu *user_fpu;
-	struct fpu *guest_fpu;
+	struct fpu_guest guest_fpu;
 
 	u64 xcr0;
 	u64 guest_supported_xcr0;
@@ -1685,8 +1684,6 @@ void kvm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
 int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
 		    int reason, bool has_error_code, u32 error_code);
 
-void kvm_free_guest_fpu(struct kvm_vcpu *vcpu);
-
 void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned long cr0);
 void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned long cr4);
 int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);

arch/x86/kernel/fpu/core.c

@@ -268,10 +268,10 @@ void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
 }
 EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
 
-void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf,
+void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
 				    unsigned int size, u32 pkru)
 {
-	struct fpstate *kstate = fpu->fpstate;
+	struct fpstate *kstate = gfpu->fpstate;
 	union fpregs_state *ustate = buf;
 	struct membuf mb = { .p = buf, .left = size };
 
@@ -284,12 +284,12 @@ void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf,
 		ustate->xsave.header.xfeatures = XFEATURE_MASK_FPSSE;
 	}
 }
-EXPORT_SYMBOL_GPL(fpu_copy_fpstate_to_kvm_uabi);
+EXPORT_SYMBOL_GPL(fpu_copy_guest_fpstate_to_uabi);
 
-int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0,
-				 u32 *vpkru)
+int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
+				   u64 xcr0, u32 *vpkru)
 {
-	struct fpstate *kstate = fpu->fpstate;
+	struct fpstate *kstate = gfpu->fpstate;
 	const union fpregs_state *ustate = buf;
 	struct pkru_state *xpkru;
 	int ret;
@@ -320,7 +320,7 @@ int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0,
 	xstate_init_xcomp_bv(&kstate->regs.xsave, kstate->xfeatures);
 	return 0;
 }
-EXPORT_SYMBOL_GPL(fpu_copy_kvm_uabi_to_fpstate);
+EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate);
 #endif /* CONFIG_KVM */
 
 void kernel_fpu_begin_mask(unsigned int kfpu_mask)

arch/x86/kvm/svm/svm.c

@@ -36,6 +36,7 @@
 #include <asm/spec-ctrl.h>
 #include <asm/cpu_device_id.h>
 #include <asm/traps.h>
+#include <asm/fpu/api.h>
 
 #include <asm/virtext.h>
 #include "trace.h"
@@ -1346,10 +1347,10 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
 		/*
 		 * SEV-ES guests maintain an encrypted version of their FPU
 		 * state which is restored and saved on VMRUN and VMEXIT.
-		 * Free the fpu structure to prevent KVM from attempting to
-		 * access the FPU state.
+		 * Mark vcpu->arch.guest_fpu->fpstate as scratch so it won't
+		 * do xsave/xrstor on it.
 		 */
-		kvm_free_guest_fpu(vcpu);
+		fpstate_set_confidential(&vcpu->arch.guest_fpu);
 	}
 
 	err = avic_init_vcpu(svm);

arch/x86/kvm/x86.c

@@ -295,8 +295,6 @@ u64 __read_mostly host_xcr0;
 u64 __read_mostly supported_xcr0;
 EXPORT_SYMBOL_GPL(supported_xcr0);
 
-static struct kmem_cache *x86_fpu_cache;
-
 static struct kmem_cache *x86_emulator_cache;
 
 /*
@@ -4705,10 +4703,11 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
 					 struct kvm_xsave *guest_xsave)
 {
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return;
 
-	fpu_copy_fpstate_to_kvm_uabi(vcpu->arch.guest_fpu, guest_xsave->region,
+	fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
+				       guest_xsave->region,
 				       sizeof(guest_xsave->region),
 				       vcpu->arch.pkru);
 }
@@ -4716,10 +4715,10 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
 static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
 					struct kvm_xsave *guest_xsave)
 {
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return 0;
 
-	return fpu_copy_kvm_uabi_to_fpstate(vcpu->arch.guest_fpu,
+	return fpu_copy_uabi_to_guest_fpstate(&vcpu->arch.guest_fpu,
 					      guest_xsave->region,
 					      supported_xcr0, &vcpu->arch.pkru);
 }
@@ -8301,18 +8300,11 @@ int kvm_arch_init(void *opaque)
 	}
 
 	r = -ENOMEM;
-	x86_fpu_cache = kmem_cache_create("x86_fpu", sizeof(struct fpu),
-					  __alignof__(struct fpu), SLAB_ACCOUNT,
-					  NULL);
-	if (!x86_fpu_cache) {
-		printk(KERN_ERR "kvm: failed to allocate cache for x86 fpu\n");
-		goto out;
-	}
 
 	x86_emulator_cache = kvm_alloc_emulator_cache();
 	if (!x86_emulator_cache) {
 		pr_err("kvm: failed to allocate cache for x86 emulator\n");
-		goto out_free_x86_fpu_cache;
+		goto out;
 	}
 
 	user_return_msrs = alloc_percpu(struct kvm_user_return_msrs);
@@ -8350,8 +8342,6 @@ int kvm_arch_init(void *opaque)
 	free_percpu(user_return_msrs);
 out_free_x86_emulator_cache:
 	kmem_cache_destroy(x86_emulator_cache);
-out_free_x86_fpu_cache:
-	kmem_cache_destroy(x86_fpu_cache);
 out:
 	return r;
 }
@@ -8378,7 +8368,6 @@ void kvm_arch_exit(void)
 	kvm_mmu_module_exit();
 	free_percpu(user_return_msrs);
 	kmem_cache_destroy(x86_emulator_cache);
-	kmem_cache_destroy(x86_fpu_cache);
 #ifdef CONFIG_KVM_XEN
 	static_key_deferred_flush(&kvm_xen_enabled);
 	WARN_ON(static_branch_unlikely(&kvm_xen_enabled.key));
@@ -9801,23 +9790,17 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
 {
 	/*
-	 * 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().
+	 * Exclude PKRU from restore as restored separately in
+	 * kvm_x86_ops.run().
 	 */
-	fpu_swap_kvm_fpu(vcpu->arch.user_fpu, vcpu->arch.guest_fpu,
-			 ~XFEATURE_MASK_PKRU);
+	fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, true);
 	trace_kvm_fpu(1);
 }
 
 /* When vcpu_run ends, restore user space FPU context. */
 static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 {
-	/*
-	 * Guests with protected state have guest_fpu == NULL which makes
-	 * swap only restore the host state.
-	 */
-	fpu_swap_kvm_fpu(vcpu->arch.guest_fpu, vcpu->arch.user_fpu, ~0ULL);
+	fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, false);
 	++vcpu->stat.fpu_reload;
 	trace_kvm_fpu(0);
 }
@@ -10398,12 +10381,12 @@ int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
 	struct fxregs_state *fxsave;
 
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return 0;
 
 	vcpu_load(vcpu);
 
-	fxsave = &vcpu->arch.guest_fpu->fpstate->regs.fxsave;
+	fxsave = &vcpu->arch.guest_fpu.fpstate->regs.fxsave;
 	memcpy(fpu->fpr, fxsave->st_space, 128);
 	fpu->fcw = fxsave->cwd;
 	fpu->fsw = fxsave->swd;
@@ -10421,12 +10404,12 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
 	struct fxregs_state *fxsave;
 
-	if (!vcpu->arch.guest_fpu)
+	if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 		return 0;
 
 	vcpu_load(vcpu);
 
-	fxsave = &vcpu->arch.guest_fpu->fpstate->regs.fxsave;
+	fxsave = &vcpu->arch.guest_fpu.fpstate->regs.fxsave;
 
 	memcpy(fxsave->st_space, fpu->fpr, 128);
 	fxsave->cwd = fpu->fcw;
@@ -10487,15 +10470,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
 	vcpu->arch.cr0 |= X86_CR0_ET;
 }
 
-void kvm_free_guest_fpu(struct kvm_vcpu *vcpu)
-{
-	if (vcpu->arch.guest_fpu) {
-		kmem_cache_free(x86_fpu_cache, vcpu->arch.guest_fpu);
-		vcpu->arch.guest_fpu = NULL;
-	}
-}
-EXPORT_SYMBOL_GPL(kvm_free_guest_fpu);
-
 int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
 {
 	if (kvm_check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
@@ -10552,22 +10526,11 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	if (!alloc_emulate_ctxt(vcpu))
 		goto free_wbinvd_dirty_mask;
 
-	vcpu->arch.user_fpu = kmem_cache_zalloc(x86_fpu_cache,
-						GFP_KERNEL_ACCOUNT);
-	if (!vcpu->arch.user_fpu) {
-		pr_err("kvm: failed to allocate userspace's fpu\n");
-		goto free_emulate_ctxt;
-	}
-
-	vcpu->arch.guest_fpu = kmem_cache_zalloc(x86_fpu_cache,
-						 GFP_KERNEL_ACCOUNT);
-	if (!vcpu->arch.guest_fpu) {
+	if (!fpu_alloc_guest_fpstate(&vcpu->arch.guest_fpu)) {
 		pr_err("kvm: failed to allocate vcpu's fpu\n");
-		goto free_user_fpu;
+		goto free_emulate_ctxt;
 	}
 
-	fpu_init_fpstate_user(vcpu->arch.user_fpu);
-	fpu_init_fpstate_user(vcpu->arch.guest_fpu);
 	fx_init(vcpu);
 
 	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
@@ -10600,9 +10563,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	return 0;
 
 free_guest_fpu:
-	kvm_free_guest_fpu(vcpu);
-free_user_fpu:
-	kmem_cache_free(x86_fpu_cache, vcpu->arch.user_fpu);
+	fpu_free_guest_fpstate(&vcpu->arch.guest_fpu);
 free_emulate_ctxt:
 	kmem_cache_free(x86_emulator_cache, vcpu->arch.emulate_ctxt);
 free_wbinvd_dirty_mask:
@@ -10651,8 +10612,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 
 	kmem_cache_free(x86_emulator_cache, vcpu->arch.emulate_ctxt);
 	free_cpumask_var(vcpu->arch.wbinvd_dirty_mask);
-	kmem_cache_free(x86_fpu_cache, vcpu->arch.user_fpu);
-	kvm_free_guest_fpu(vcpu);
+	fpu_free_guest_fpstate(&vcpu->arch.guest_fpu);
 
 	kvm_hv_vcpu_uninit(vcpu);
 	kvm_pmu_destroy(vcpu);
@@ -10704,8 +10664,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	kvm_async_pf_hash_reset(vcpu);
 	vcpu->arch.apf.halted = false;
 
-	if (vcpu->arch.guest_fpu && kvm_mpx_supported()) {
-		struct fpstate *fpstate = vcpu->arch.guest_fpu->fpstate;
+	if (vcpu->arch.guest_fpu.fpstate && kvm_mpx_supported()) {
+		struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
 
 		/*
 		 * To avoid have the INIT path from kvm_apic_has_events() that be