1 files changed, 39 insertions, 14 deletions

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index ea138583dd92..aefd412a23dc 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -37,6 +37,7 @@ DEFINE_PER_CPU(u64, xfd_state);
 /* The FPU state configuration data for kernel and user space */
 struct fpu_state_config	fpu_kernel_cfg __ro_after_init;
 struct fpu_state_config fpu_user_cfg __ro_after_init;
+struct vcpu_fpu_config guest_default_cfg __ro_after_init;
 
 /*
  * Represents the initial FPU state. It's mostly (but not completely) zeroes,
@@ -217,7 +218,7 @@ void fpu_reset_from_exception_fixup(void)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
+static void __fpstate_reset(struct fpstate *fpstate);
 
 static void fpu_lock_guest_permissions(void)
 {
@@ -242,19 +243,21 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	struct fpstate *fpstate;
 	unsigned int size;
 
-	size = fpu_kernel_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+	size = guest_default_cfg.size + ALIGN(offsetof(struct fpstate, regs), 64);
+
 	fpstate = vzalloc(size);
 	if (!fpstate)
 		return false;
 
-	/* Leave xfd to 0 (the reset value defined by spec) */
-	__fpstate_reset(fpstate, 0);
-	fpstate_init_user(fpstate);
+	/* Initialize indicators to reflect properties of the fpstate */
 	fpstate->is_valloc	= true;
 	fpstate->is_guest	= true;
 
+	__fpstate_reset(fpstate);
+	fpstate_init_user(fpstate);
+
 	gfpu->fpstate		= fpstate;
-	gfpu->xfeatures		= fpu_kernel_cfg.default_features;
+	gfpu->xfeatures		= guest_default_cfg.features;
 
 	/*
 	 * KVM sets the FP+SSE bits in the XSAVE header when copying FPU state
@@ -541,28 +544,50 @@ void fpstate_init_user(struct fpstate *fpstate)
 		fpstate_init_fstate(fpstate);
 }
 
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd)
+static void __fpstate_reset(struct fpstate *fpstate)
 {
-	/* Initialize sizes and feature masks */
-	fpstate->size		= fpu_kernel_cfg.default_size;
+	/*
+	 * Supervisor features (and thus sizes) may diverge between guest
+	 * FPUs and host FPUs, as some supervisor features are supported
+	 * for guests despite not being utilized by the host. User
+	 * features and sizes are always identical, which allows for
+	 * common guest and userspace ABI.
+	 *
+	 * For the host, set XFD to the kernel's desired initialization
+	 * value. For guests, set XFD to its architectural RESET value.
+	 */
+	if (fpstate->is_guest) {
+		fpstate->size		= guest_default_cfg.size;
+		fpstate->xfeatures	= guest_default_cfg.features;
+		fpstate->xfd		= 0;
+	} else {
+		fpstate->size		= fpu_kernel_cfg.default_size;
+		fpstate->xfeatures	= fpu_kernel_cfg.default_features;
+		fpstate->xfd		= init_fpstate.xfd;
+	}
+
 	fpstate->user_size	= fpu_user_cfg.default_size;
-	fpstate->xfeatures	= fpu_kernel_cfg.default_features;
 	fpstate->user_xfeatures	= fpu_user_cfg.default_features;
-	fpstate->xfd		= xfd;
 }
 
 void fpstate_reset(struct fpu *fpu)
 {
 	/* Set the fpstate pointer to the default fpstate */
 	fpu->fpstate = &fpu->__fpstate;
-	__fpstate_reset(fpu->fpstate, init_fpstate.xfd);
+	__fpstate_reset(fpu->fpstate);
 
 	/* Initialize the permission related info in fpu */
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;
 	fpu->perm.__state_size		= fpu_kernel_cfg.default_size;
 	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;
-	/* Same defaults for guests */
-	fpu->guest_perm = fpu->perm;
+
+	fpu->guest_perm.__state_perm	= guest_default_cfg.features;
+	fpu->guest_perm.__state_size	= guest_default_cfg.size;
+	/*
+	 * User features and sizes are always identical between host and
+	 * guest FPUs, which allows for common guest and userspace ABI.
+	 */
+	fpu->guest_perm.__user_state_size = fpu_user_cfg.default_size;
 }
 
 static inline void fpu_inherit_perms(struct fpu *dst_fpu)