Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6226686954c4cce3d63ffe1777e60360fcbf0b83
Commit:     6226686954c4cce3d63ffe1777e60360fcbf0b83
Parent:     93a0039c8d93074d5f92dfb69f6a7d453905d002
Author:     Avi Kivity <[EMAIL PROTECTED]>
AuthorDate: Tue Nov 20 13:15:52 2007 +0200
Committer:  Avi Kivity <[EMAIL PROTECTED]>
CommitDate: Wed Jan 30 17:53:09 2008 +0200

    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 <[EMAIL PROTECTED]>
---
 drivers/kvm/x86_emulate.c |   38 ++++++++++++++++++++++++++++++++++++--
 drivers/kvm/x86_emulate.h |    7 +++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

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 @@ static u16 twobyte_table[256] = {
 /* 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 @@ static u16 twobyte_table[256] = {
                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.
diff --git a/drivers/kvm/x86_emulate.h b/drivers/kvm/x86_emulate.h
index a62bf14..4603b2b 100644
--- a/drivers/kvm/x86_emulate.h
+++ b/drivers/kvm/x86_emulate.h
@@ -108,6 +108,12 @@ struct operand {
        unsigned long val, orig_val, *ptr;
 };
 
+struct fetch_cache {
+       u8 data[15];
+       unsigned long start;
+       unsigned long end;
+};
+
 struct decode_cache {
        u8 twobyte;
        u8 b;
@@ -130,6 +136,7 @@ struct decode_cache {
        u8 use_modrm_ea;
        unsigned long modrm_ea;
        unsigned long modrm_val;
+       struct fetch_cache fetch;
 };
 
 struct x86_emulate_ctxt {
-
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