KVM: x86 emulator: prefetch up to 15 bytes of the instruction executed
Instead of fetching one byte at a time, prefetch 15 bytes (or until the next
page boundary) to avoid guest page table walks.
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 8e2162f..6e7f774 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -414,8 +414,7 @@
/* Fetch next part of the instruction being emulated. */
#define insn_fetch(_type, _size, _eip) \
({ unsigned long _x; \
- rc = ops->read_std((unsigned long)(_eip) + ctxt->cs_base, &_x, \
- (_size), ctxt->vcpu); \
+ rc = do_insn_fetch(ctxt, ops, (_eip), &_x, (_size)); \
if (rc != 0) \
goto done; \
(_eip) += (_size); \
@@ -446,6 +445,41 @@
register_address_increment(c->eip, rel); \
} while (0)
+static int do_fetch_insn_byte(struct x86_emulate_ctxt *ctxt,
+ struct x86_emulate_ops *ops,
+ unsigned long linear, u8 *dest)
+{
+ struct fetch_cache *fc = &ctxt->decode.fetch;
+ int rc;
+ int size;
+
+ if (linear < fc->start || linear >= fc->end) {
+ size = min(15UL, PAGE_SIZE - offset_in_page(linear));
+ rc = ops->read_std(linear, fc->data, size, ctxt->vcpu);
+ if (rc)
+ return rc;
+ fc->start = linear;
+ fc->end = linear + size;
+ }
+ *dest = fc->data[linear - fc->start];
+ return 0;
+}
+
+static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
+ struct x86_emulate_ops *ops,
+ unsigned long eip, void *dest, unsigned size)
+{
+ int rc = 0;
+
+ eip += ctxt->cs_base;
+ while (size--) {
+ rc = do_fetch_insn_byte(ctxt, ops, eip++, dest++);
+ if (rc)
+ return rc;
+ }
+ return 0;
+}
+
/*
* Given the 'reg' portion of a ModRM byte, and a register block, return a
* pointer into the block that addresses the relevant register.