linux-kernel - [PATCH v2 5/6] x86/fpu/xstate: Create guest fpstate with guest specific config

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Message-ID: <20241126101710.62492-6-chao.gao@intel.com>
Date: Tue, 26 Nov 2024 18:17:09 +0800
From: Chao Gao <chao.gao@...el.com>
To: tglx@...utronix.de,
	dave.hansen@...el.com,
	x86@...nel.org,
	seanjc@...gle.com,
	pbonzini@...hat.com,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: peterz@...radead.org,
	rick.p.edgecombe@...el.com,
	mlevitsk@...hat.com,
	weijiang.yang@...el.com,
	john.allen@....com,
	Chao Gao <chao.gao@...el.com>
Subject: [PATCH v2 5/6] x86/fpu/xstate: Create guest fpstate with guest specific config

From: Yang Weijiang <weijiang.yang@...el.com>

Use fpu_guest_cfg to calculate guest fpstate settings, open code for
__fpstate_reset() to avoid using kernel FPU config.

Below configuration steps are currently enforced to get guest fpstate:
1) Kernel sets up guest FPU settings in fpu__init_system_xstate().
2) User space sets vCPU thread group xstate permits via arch_prctl().
3) User space creates guest fpstate via __fpu_alloc_init_guest_fpstate()
   for vcpu thread.
4) User space enables guest dynamic xfeatures and re-allocate guest
   fpstate.

By adding kernel dynamic xfeatures in above #1 and #2, guest xstate area
size is expanded to hold (fpu_kernel_cfg.default_features | kernel dynamic
xfeatures | user dynamic xfeatures), then host xsaves/xrstors can operate
for all guest xfeatures.

The user_* fields remain unchanged for compatibility with KVM uAPIs.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
 arch/x86/kernel/fpu/core.c | 39 +++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 9e2e5c46cf28..00d7dcf45b34 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -194,8 +194,6 @@ void fpu_reset_from_exception_fixup(void)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
-
 static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 {
 	struct fpu_state_perm *fpuperm;
@@ -216,25 +214,48 @@ static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 	gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
 }
 
-bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
+static struct fpstate *__fpu_alloc_init_guest_fpstate(struct fpu_guest *gfpu)
 {
 	struct fpstate *fpstate;
 	unsigned int size;
 
-	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+	/*
+	 * fpu_guest_cfg.default_size is initialized to hold all enabled
+	 * xfeatures except the user dynamic xfeatures. If the user dynamic
+	 * xfeatures are enabled, the guest fpstate will be re-allocated to
+	 * hold all guest enabled xfeatures, so omit user dynamic xfeatures
+	 * here.
+	 */
+	size = fpu_guest_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+
 	fpstate = vzalloc(size);
 	if (!fpstate)
-		return false;
+		return NULL;
+	/*
+	 * Initialize sizes and feature masks, use fpu_user_cfg.*
+	 * for user_* settings for compatibility of exiting uAPIs.
+	 */
+	fpstate->size		= fpu_guest_cfg.default_size;
+	fpstate->xfeatures	= fpu_guest_cfg.default_features;
+	fpstate->user_size	= fpu_user_cfg.default_size;
+	fpstate->user_xfeatures	= fpu_user_cfg.default_features;
+	fpstate->xfd		= 0;
 
-	/* Leave xfd to 0 (the reset value defined by spec) */
-	__fpstate_reset(fpstate, 0);
 	fpstate_init_user(fpstate);
 	fpstate->is_valloc	= true;
 	fpstate->is_guest	= true;
 
 	gfpu->fpstate		= fpstate;
-	gfpu->xfeatures		= fpu_user_cfg.default_features;
-	gfpu->perm		= fpu_user_cfg.default_features;
+	gfpu->xfeatures		= fpu_guest_cfg.default_features;
+	gfpu->perm		= fpu_guest_cfg.default_features;
+
+	return fpstate;
+}
+
+bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
+{
+	if (!__fpu_alloc_init_guest_fpstate(gfpu))
+		return false;
 
 	/*
 	 * KVM sets the FP+SSE bits in the XSAVE header when copying FPU state
-- 
2.46.1