linux-kernel - [PATCH v2 3/7] x86/kvm/vmx: Get rid of segment

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Message-Id: <ed27c1109c5ced553b91e2a6be3c9fd8120c4181.1487704145.git.luto@kernel.org>
Date:   Tue, 21 Feb 2017 11:14:10 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>, X86 ML <x86@...nel.org>
Cc:     kvm list <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Thomas Garnier <thgarnie@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH v2 3/7] x86/kvm/vmx: Get rid of segment_base() on 64-bit kernels

It was a bit buggy (it didn't list all segment types that needed
64-bit fixups), but the bug was irrelevant because it wasn't called
in any interesting context on 64-bit kernels and was only used for
code and data segments on 32-bit kernels.

To avoid confusion, make it explicitly 32-bit only.

Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Jim Mattson <jmattson@...gle.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kvm/vmx.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 46420aaf1684..b1810a0edec3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2059,6 +2059,12 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
 	}
 }
 
+#ifdef CONFIG_X86_32
+/*
+ * On 32-bit kernels, VM exits still load the FS and GS bases from the
+ * VMCS rather than the segment table.  KVM uses this helper to figure
+ * out the current bases to poke them into the VMCS before entry.
+ */
 static unsigned long segment_base(u16 selector)
 {
 	struct desc_ptr *gdt = this_cpu_ptr(&host_gdt);
@@ -2081,12 +2087,9 @@ static unsigned long segment_base(u16 selector)
 	}
 	d = (struct desc_struct *)(table_base + (selector & ~7));
 	v = get_desc_base(d);
-#ifdef CONFIG_X86_64
-       if (d->s == 0 && (d->type == 2 || d->type == 9 || d->type == 11))
-               v |= ((unsigned long)((struct ldttss_desc64 *)d)->base3) << 32;
-#endif
 	return v;
 }
+#endif
 
 static void vmx_save_host_state(struct kvm_vcpu *vcpu)
 {
-- 
2.9.3