x86/fpu: Add uabi_size to guest_fpu

Userspace needs to inquire KVM about the buffer size to work
with the new KVM_SET_XSAVE and KVM_GET_XSAVE2. Add the size info
to guest_fpu for KVM to access.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-18-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -522,6 +522,11 @@ struct fpu_guest {
 	 */
 	u64				xfd_err;
 
+	/*
+	 * @uabi_size:			Size required for save/restore
+	 */
+	unsigned int			uabi_size;
+
 	/*
 	 * @fpstate:			Pointer to the allocated guest fpstate
 	 */

arch/x86/kernel/fpu/core.c

@@ -240,6 +240,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	gfpu->fpstate		= fpstate;
 	gfpu->xfeatures		= fpu_user_cfg.default_features;
 	gfpu->perm		= fpu_user_cfg.default_features;
+	gfpu->uabi_size		= fpu_user_cfg.default_size;
 	fpu_init_guest_permissions(gfpu);
 
 	return true;

arch/x86/kernel/fpu/xstate.c

@@ -1545,6 +1545,7 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
 		newfps->is_confidential = curfps->is_confidential;
 		newfps->in_use = curfps->in_use;
 		guest_fpu->xfeatures |= xfeatures;
+		guest_fpu->uabi_size = usize;
 	}
 
 	fpregs_lock();