linux-kernel - [patch 3/6] x86/fpu: Make XFD initialization in __fpstate

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Message-ID: <20211214024947.935581464@linutronix.de>
Date:   Tue, 14 Dec 2021 03:50:24 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Jing Liu <jing2.liu@...ux.intel.com>,
        Yang Zhong <yang.zhong@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org,
        kvm@...r.kernel.org, Sean Christoperson <seanjc@...gle.com>,
        Jin Nakajima <jun.nakajima@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jing Liu <jing2.liu@...el.com>
Subject: [patch 3/6] x86/fpu: Make XFD initialization in __fpstate_reset() a
 function argument

From: Jing Liu <jing2.liu@...el.com>

vCPU threads are different from native tasks regarding to the initial XFD
value. While all native tasks follow a fixed value (init_fpstate::xfd)
established by the FPU core at boot, vCPU threads need to obey the reset
value (i.e. ZERO) defined by the specification, to meet the expectation of
the guest.

Let the caller supply an argument and adjust the host and guest related
invocations accordingly.

[ tglx: Make it explicit via function argument ]

Signed-off-by: Jing Liu <jing2.liu@...el.com>
Signed-off-by: Yang Zhong <yang.zhong@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
---
 arch/x86/kernel/fpu/core.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -199,7 +199,7 @@ void fpu_reset_from_exception_fixup(void
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate);
+static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
 
 static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 {
@@ -231,7 +231,8 @@ bool fpu_alloc_guest_fpstate(struct fpu_
 	if (!fpstate)
 		return false;
 
-	__fpstate_reset(fpstate);
+	/* 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;
@@ -454,21 +455,21 @@ void fpstate_init_user(struct fpstate *f
 		fpstate_init_fstate(fpstate);
 }
 
-static void __fpstate_reset(struct fpstate *fpstate)
+static void __fpstate_reset(struct fpstate *fpstate, u64 xfd)
 {
 	/* Initialize sizes and feature masks */
 	fpstate->size		= fpu_kernel_cfg.default_size;
 	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		= init_fpstate.xfd;
+	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);
+	__fpstate_reset(fpu->fpstate, init_fpstate.xfd);
 
 	/* Initialize the permission related info in fpu */
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;