linux-kernel - [PATCH v6 02/21] x86/fpu: Prepare guest FPU for dynamically enabled FPU features

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Date:   Fri,  7 Jan 2022 13:54:53 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     guang.zeng@...el.com, jing2.liu@...el.com, kevin.tian@...el.com,
        seanjc@...gle.com, tglx@...utronix.de, wei.w.wang@...el.com,
        yang.zhong@...el.com
Subject: [PATCH v6 02/21] x86/fpu: Prepare guest FPU for dynamically enabled FPU features

From: Thomas Gleixner <tglx@...utronix.de>

To support dynamically enabled FPU features for guests prepare the guest
pseudo FPU container to keep track of the currently enabled xfeatures and
the guest permissions.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jing Liu <jing2.liu@...el.com>
Signed-off-by: Yang Zhong <yang.zhong@...el.com>
Message-Id: <20220105123532.12586-3-yang.zhong@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/include/asm/fpu/types.h | 13 +++++++++++++
 arch/x86/kernel/fpu/core.c       | 26 +++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 6ddf80637697..c752d0aa23a4 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -504,6 +504,19 @@ struct fpu {
  * Guest pseudo FPU container
  */
 struct fpu_guest {
+	/*
+	 * @xfeatures:			xfeature bitmap of features which are
+	 *				currently enabled for the guest vCPU.
+	 */
+	u64				xfeatures;
+
+	/*
+	 * @perm:			xfeature bitmap of features which are
+	 *				permitted to be enabled for the guest
+	 *				vCPU.
+	 */
+	u64				perm;
+
 	/*
 	 * @fpstate:			Pointer to the allocated guest fpstate
 	 */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index ab19b3d8b2f7..eddeeb4ed2f5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -201,6 +201,26 @@ void fpu_reset_from_exception_fixup(void)
 #if IS_ENABLED(CONFIG_KVM)
 static void __fpstate_reset(struct fpstate *fpstate);
 
+static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
+{
+	struct fpu_state_perm *fpuperm;
+	u64 perm;
+
+	if (!IS_ENABLED(CONFIG_X86_64))
+		return;
+
+	spin_lock_irq(&current->sighand->siglock);
+	fpuperm = &current->group_leader->thread.fpu.guest_perm;
+	perm = fpuperm->__state_perm;
+
+	/* First fpstate allocation locks down permissions. */
+	WRITE_ONCE(fpuperm->__state_perm, perm | FPU_GUEST_PERM_LOCKED);
+
+	spin_unlock_irq(&current->sighand->siglock);
+
+	gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
+}
+
 bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 {
 	struct fpstate *fpstate;
@@ -216,7 +236,11 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	fpstate->is_valloc	= true;
 	fpstate->is_guest	= true;
 
-	gfpu->fpstate = fpstate;
+	gfpu->fpstate		= fpstate;
+	gfpu->xfeatures		= fpu_user_cfg.default_features;
+	gfpu->perm		= fpu_user_cfg.default_features;
+	fpu_init_guest_permissions(gfpu);
+
 	return true;
 }
 EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);
-- 
2.31.1