[Xen-devel] [PATCH v3 1/3] x86/vmx: introduce vmx_find_msr()

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Modify vmx_add_msr() to use a variation of insertion sort algorithm:
find a place for the new entry and shift all subsequent elements before
insertion.

The new vmx_find_msr() exploits the fact that MSR list is now sorted
and reuses the existing code for binary search.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2 --> v3:
- Now "idx < *msr_count" is compared before "(*msr_area)[idx].index"
  in order to eliminate possible out-of-bounds access

 xen/arch/x86/hvm/vmx/vmcs.c        | 45 ++++++++++++++++++++++++++++++++++++--
 xen/include/asm-x86/hvm/vmx/vmcs.h |  1 +
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 5306a48..977106f 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1320,6 +1320,44 @@ static int construct_vmcs(struct vcpu *v)
     return 0;
 }
 
+static int vmx_msr_entry_key_cmp(const void *key, const void *elt)
+{
+    const u32 *msr = key;
+    const struct vmx_msr_entry *entry = elt;
+
+    if ( *msr > entry->index )
+        return 1;
+    if ( *msr < entry->index )
+        return -1;
+
+    return 0;
+}
+
+struct vmx_msr_entry *vmx_find_msr(u32 msr, int type)
+{
+    struct vcpu *curr = current;
+    unsigned int msr_count;
+    struct vmx_msr_entry *msr_area;
+
+    if ( type == VMX_GUEST_MSR )
+    {
+        msr_count = curr->arch.hvm_vmx.msr_count;
+        msr_area = curr->arch.hvm_vmx.msr_area;
+    }
+    else
+    {
+        ASSERT(type == VMX_HOST_MSR);
+        msr_count = curr->arch.hvm_vmx.host_msr_count;
+        msr_area = curr->arch.hvm_vmx.host_msr_area;
+    }
+
+    if ( msr_area == NULL )
+        return NULL;
+
+    return bsearch(&msr, msr_area, msr_count, sizeof(struct vmx_msr_entry),
+                   vmx_msr_entry_key_cmp);
+}
+
 int vmx_read_guest_msr(u32 msr, u64 *val)
 {
     struct vcpu *curr = current;
@@ -1388,14 +1426,17 @@ int vmx_add_msr(u32 msr, int type)
             __vmwrite(VM_EXIT_MSR_LOAD_ADDR, virt_to_maddr(*msr_area));
     }
 
-    for ( idx = 0; idx < *msr_count; idx++ )
+    for ( idx = 0; idx < *msr_count && (*msr_area)[idx].index <= msr; idx++ )
         if ( (*msr_area)[idx].index == msr )
             return 0;
 
     if ( *msr_count == (PAGE_SIZE / sizeof(struct vmx_msr_entry)) )
         return -ENOSPC;
 
-    msr_area_elem = *msr_area + *msr_count;
+    memmove(*msr_area + idx + 1, *msr_area + idx,
+            sizeof(*msr_area_elem) * (*msr_count - idx));
+
+    msr_area_elem = *msr_area + idx;
     msr_area_elem->index = msr;
     msr_area_elem->mbz = 0;
 
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h 
b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 4ee01da..4945b78 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -530,6 +530,7 @@ void vmx_disable_intercept_for_msr(struct vcpu *v, u32 msr, 
int type);
 void vmx_enable_intercept_for_msr(struct vcpu *v, u32 msr, int type);
 int vmx_read_guest_msr(u32 msr, u64 *val);
 int vmx_write_guest_msr(u32 msr, u64 val);
+struct vmx_msr_entry *vmx_find_msr(u32 msr, int type);
 int vmx_add_msr(u32 msr, int type);
 void vmx_vmcs_switch(paddr_t from, paddr_t to);
 void vmx_set_eoi_exit_bitmap(struct vcpu *v, u8 vector);
-- 
2.9.3


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