linux-kernel - [PATCH 4/8] x86/kvm: Remove host CR0.TS manipulation

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Message-Id: <b212064922537c05d0c81d931fc4dbe769127ce7.1477951965.git.luto@kernel.org>
Date:   Mon, 31 Oct 2016 15:18:45 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Rusty Russell <rusty@...tcorp.com.au>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 4/8] x86/kvm: Remove host CR0.TS manipulation

Now that x86 always uses eager fpu switching on the host, there's no
need for KVM to manipulate the host's CR0.TS.

This should be both simpler and faster.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kvm/vmx.c | 12 ++++--------
 arch/x86/kvm/x86.c |  5 -----
 2 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cf1b16dbc98a..531c44633190 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2144,12 +2144,6 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
 #endif
 	if (vmx->host_state.msr_host_bndcfgs)
 		wrmsrl(MSR_IA32_BNDCFGS, vmx->host_state.msr_host_bndcfgs);
-	/*
-	 * If the FPU is not active (through the host task or
-	 * the guest vcpu), then restore the cr0.TS bit.
-	 */
-	if (!fpregs_active() && !vmx->vcpu.guest_fpu_loaded)
-		stts();
 	load_gdt(this_cpu_ptr(&host_gdt));
 }
 
@@ -4871,9 +4865,11 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
 	u32 low32, high32;
 	unsigned long tmpl;
 	struct desc_ptr dt;
-	unsigned long cr4;
+	unsigned long cr0, cr4;
 
-	vmcs_writel(HOST_CR0, read_cr0() & ~X86_CR0_TS);  /* 22.2.3 */
+	cr0 = read_cr0();
+	WARN_ON(cr0 & X86_CR0_TS);
+	vmcs_writel(HOST_CR0, cr0);  /* 22.2.3 */
 	vmcs_writel(HOST_CR3, read_cr3());  /* 22.2.3  FIXME: shadow tables */
 
 	/* Save the most likely value for this task's CR4 in the VMCS. */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d5700263dad2..123d428d319a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5060,11 +5060,6 @@ static void emulator_get_fpu(struct x86_emulate_ctxt *ctxt)
 {
 	preempt_disable();
 	kvm_load_guest_fpu(emul_to_vcpu(ctxt));
-	/*
-	 * CR0.TS may reference the host fpu state, not the guest fpu state,
-	 * so it may be clear at this point.
-	 */
-	clts();
 }
 
 static void emulator_put_fpu(struct x86_emulate_ctxt *ctxt)
-- 
2.7.4