File 5b3cab8f-1-VMX-factor-out-locate_msr_entry.patch of Package xen.8389
# Commit 4d94828cf11104256dccea1fa7762f00575dfaa0
# Date 2018-07-04 12:12:15 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/vmx: Factor locate_msr_entry() out of vmx_find_msr() and vmx_add_msr()
Instead of having multiple algorithms searching the MSR lists, implement a
single one. It has the semantics required by vmx_add_msr(), to identify the
position in which an MSR should live, if it isn't already present.
There will be a marginal improvement for vmx_find_msr() by avoiding the
function pointer calls to vmx_msr_entry_key_cmp(), and a major improvement for
vmx_add_msr() by using a binary search instead of a linear search.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1283,24 +1283,36 @@ static int construct_vmcs(struct vcpu *v
return rc;
}
-static int vmx_msr_entry_key_cmp(const void *key, const void *elt)
+/*
+ * Search an MSR list looking for an MSR entry, or the slot in which it should
+ * live (to keep the data sorted) if an entry is not found.
+ *
+ * The return pointer is guaranteed to be bounded by start and end. However,
+ * it may point at end, and may be invalid for the caller to dereference.
+ */
+static struct vmx_msr_entry *locate_msr_entry(
+ struct vmx_msr_entry *start, struct vmx_msr_entry *end, uint32_t msr)
{
- const u32 *msr = key;
- const struct vmx_msr_entry *entry = elt;
+ while ( start < end )
+ {
+ struct vmx_msr_entry *mid = start + (end - start) / 2;
- if ( *msr > entry->index )
- return 1;
- if ( *msr < entry->index )
- return -1;
+ if ( msr < mid->index )
+ end = mid;
+ else if ( msr > mid->index )
+ start = mid + 1;
+ else
+ return mid;
+ }
- return 0;
+ return start;
}
struct vmx_msr_entry *vmx_find_msr(uint32_t msr, enum vmx_msr_list_type type)
{
struct vcpu *curr = current;
struct arch_vmx_struct *vmx = &curr->arch.hvm_vmx;
- struct vmx_msr_entry *start = NULL;
+ struct vmx_msr_entry *start = NULL, *ent, *end;
unsigned int total;
switch ( type )
@@ -1322,7 +1334,10 @@ struct vmx_msr_entry *vmx_find_msr(uint3
if ( !start )
return NULL;
- return bsearch(&msr, start, total, sizeof(*start), vmx_msr_entry_key_cmp);
+ end = start + total;
+ ent = locate_msr_entry(start, end, msr);
+
+ return ((ent < end) && (ent->index == msr)) ? ent : NULL;
}
int vmx_add_msr(uint32_t msr, enum vmx_msr_list_type type)
@@ -1374,10 +1389,10 @@ int vmx_add_msr(uint32_t msr, enum vmx_m
start = *ptr;
end = start + total;
+ ent = locate_msr_entry(start, end, msr);
- for ( ent = start; ent < end && ent->index <= msr; ++ent )
- if ( ent->index == msr )
- return 0;
+ if ( (ent < end) && (ent->index == msr) )
+ return 0;
if ( total == (PAGE_SIZE / sizeof(*ent)) )
return -ENOSPC;