linux-kernel - [PATCH 02/19] x86/fpu: Prepare KVM for dynamically enabled states

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Date:   Tue,  7 Dec 2021 19:03:42 -0500
From:   Yang Zhong <yang.zhong@...el.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        yang.zhong@...el.com
Subject: [PATCH 02/19] x86/fpu: Prepare KVM for dynamically enabled states

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

Add more fields for tracking per-vCPU permissions for dynamic XSTATE
components:

  - user_xfeatures

    Track which features are currently enabled for the vCPU

  - user_perm

    Copied from guest_perm of the group leader thread. The first
    vCPU which does the copy locks the guest_perm

  - realloc_request

    KVM sets this field to request dynamically-enabled features
    which require reallocation of @fpstate

Initialize those fields properly.

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>
---
 arch/x86/include/asm/fpu/types.h | 23 +++++++++++++++++++++++
 arch/x86/kernel/fpu/core.c       | 26 +++++++++++++++++++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 6ddf80637697..861cffca3209 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -504,6 +504,29 @@ struct fpu {
  * Guest pseudo FPU container
  */
 struct fpu_guest {
+	/*
+	 * @user_xfeatures:		xfeature bitmap of features which are
+	 *				currently enabled for the guest vCPU.
+	 */
+	u64				user_xfeatures;
+
+	/*
+	 * @user_perm:			xfeature bitmap of features which are
+	 *				permitted to be enabled for the guest
+	 *				vCPU.
+	 */
+	u64				user_perm;
+
+	/*
+	 * @realloc_request:		xfeature bitmap of features which are
+	 *				requested to be enabled dynamically
+	 *				which requires reallocation of @fpstate
+	 *
+	 *				Set by an intercept handler and
+	 *				evaluated in fpu_swap_kvm_fpstate()
+	 */
+	u64				realloc_request;
+
 	/*
 	 * @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..fe592799508c 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->user_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->user_xfeatures	= fpu_user_cfg.default_features;
+	gfpu->user_perm		= fpu_user_cfg.default_features;
+	fpu_init_guest_permissions(gfpu);
+
 	return true;
 }
 EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);