linux-kernel - [PATCH v4 4/4] KVM: VMX: Simplify segment

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Message-Id: <20170216215438.126111-4-thgarnie@google.com>
Date:   Thu, 16 Feb 2017 13:54:38 -0800
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Garnier <thgarnie@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...capital.net>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Jiri Kosina <jikos@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Borislav Petkov <bp@...e.de>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Brian Gerst <brgerst@...il.com>,
        He Chen <he.chen@...ux.intel.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Joerg Roedel <joro@...tes.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-efi@...r.kernel.org, xen-devel@...ts.xenproject.org,
        lguest@...ts.ozlabs.org, kvm@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: [PATCH v4 4/4] KVM: VMX: Simplify segment_base

The KVM segment_base function is confusing. This patch replaces integers
with appropriate flags, simplify constructs and add comments.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
Based on next-20170213
---
 arch/x86/kvm/vmx.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 99167f20bc34..91e619269128 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2060,27 +2060,37 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
 static unsigned long segment_base(u16 selector)
 {
 	struct desc_struct *d;
-	unsigned long table_base;
+	struct desc_struct *table_base;
 	unsigned long v;
+	u32 high32;
 
-	if (!(selector & ~3))
+	if (!(selector & ~SEGMENT_RPL_MASK))
 		return 0;
 
-	table_base = get_current_gdt_rw_vaddr();
-
-	if (selector & 4) {           /* from ldt */
+	/* LDT selector */
+	if ((selector & SEGMENT_TI_MASK) == SEGMENT_LDT) {
 		u16 ldt_selector = kvm_read_ldt();
 
-		if (!(ldt_selector & ~3))
+		if (!(ldt_selector & ~SEGMENT_RPL_MASK))
 			return 0;
 
-		table_base = segment_base(ldt_selector);
+		table_base = (struct desc_struct *)segment_base(ldt_selector);
+	} else {
+		table_base = get_current_gdt_rw();
 	}
-	d = (struct desc_struct *)(table_base + (selector & ~7));
+
+	d = table_base + (selector >> 3);
 	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;
+	/*
+	 * Extend the virtual address if we have a system descriptor entry for
+	 * LDT or TSS (available or busy).
+	 */
+	if (d->s == 0 && (d->type == DESC_LDT || d->type == DESC_TSS ||
+			  d->type == 11/*Busy TSS */)) {
+		high32 = ((struct ldttss_desc64 *)d)->base3;
+		v |= (u64)high32 << 32;
+	}
 #endif
 	return v;
 }
-- 
2.11.0.483.g087da7b7c-goog