linux-kernel - [PATCH 05/19] x86/fpu: Move xfd initialization out of __fpstate

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Date:   Tue,  7 Dec 2021 19:03:45 -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 05/19] x86/fpu: Move xfd initialization out of __fpstate_reset() to the callers

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)
defined by fpu core, vCPU threads need to obey the reset value
(i.e. ZERO) defined by the spec, to meet the expectation of the guest.

Move xfd initialization out of __fpstate_reset() to the callers for
choosing a specific value.

Signed-off-by: Jing Liu <jing2.liu@...el.com>
Signed-off-by: Yang Zhong <yang.zhong@...el.com>
---
 arch/x86/kernel/fpu/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index fe592799508c..fae44fa27cdb 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -231,6 +231,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
 	if (!fpstate)
 		return false;
 
+	/* Leave xfd to 0 (the reset value defined by spec) */
 	__fpstate_reset(fpstate);
 	fpstate_init_user(fpstate);
 	fpstate->is_valloc	= true;
@@ -461,7 +462,6 @@ static void __fpstate_reset(struct fpstate *fpstate)
 	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;
 }
 
 void fpstate_reset(struct fpu *fpu)
@@ -469,6 +469,7 @@ void fpstate_reset(struct fpu *fpu)
 	/* Set the fpstate pointer to the default fpstate */
 	fpu->fpstate = &fpu->__fpstate;
 	__fpstate_reset(fpu->fpstate);
+	fpu->fpstate->xfd		= init_fpstate.xfd;
 
 	/* Initialize the permission related info in fpu */
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;