[Xen-devel] [PATCH v4 4/4] KVM: VMX: Simplify segment_base

[Thomas Garnier <thgarnie@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
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


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