KVM: x86 emulator: introduce pio in string read ahead.

To optimize "rep ins" instruction do IO in big chunks ahead of time
instead of doing it only when required during instruction emulation.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 41 insertions, 5 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6de6ad1610d8..ab3fff5bf7c4 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1257,6 +1257,36 @@ done:
         return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
 }
 
+static int pio_in_emulated(struct x86_emulate_ctxt *ctxt,
+                           struct x86_emulate_ops *ops,
+                           unsigned int size, unsigned short port,
+                           void *dest)
+{
+        struct read_cache *rc = &ctxt->decode.io_read;
+
+        if (rc->pos == rc->end) { /* refill pio read ahead */
+                struct decode_cache *c = &ctxt->decode;
+                unsigned int in_page, n;
+                unsigned int count = c->rep_prefix ?
+                        address_mask(c, c->regs[VCPU_REGS_RCX]) : 1;
+                in_page = (ctxt->eflags & EFLG_DF) ?
+                        offset_in_page(c->regs[VCPU_REGS_RDI]) :
+                        PAGE_SIZE - offset_in_page(c->regs[VCPU_REGS_RDI]);
+                n = min(min(in_page, (unsigned int)sizeof(rc->data)) / size,
+                        count);
+                if (n == 0)
+                        n = 1;
+                rc->pos = rc->end = 0;
+                if (!ops->pio_in_emulated(size, port, rc->data, n, ctxt->vcpu))
+                        return 0;
+                rc->end = n * size;
+        }
+
+        memcpy(dest, rc->data + rc->pos, size);
+        rc->pos += size;
+        return 1;
+}
+
 static u32 desc_limit_scaled(struct desc_struct *desc)
 {
         u32 limit = get_desc_limit(desc);
@@ -2622,8 +2652,8 @@ special_insn:
                         kvm_inject_gp(ctxt->vcpu, 0);
                         goto done;
                 }
-                if (!ops->pio_in_emulated(c->dst.bytes, c->regs[VCPU_REGS_RDX],
-                                          &c->dst.val, 1, ctxt->vcpu))
+                if (!pio_in_emulated(ctxt, ops, c->dst.bytes,
+                                     c->regs[VCPU_REGS_RDX], &c->dst.val))
                         goto done; /* IO is needed, skip writeback */
                 break;
         case 0x6e:              /* outsb */
@@ -2839,8 +2869,8 @@ special_insn:
                         kvm_inject_gp(ctxt->vcpu, 0);
                         goto done;
                 }
-                if (!ops->pio_in_emulated(c->dst.bytes, c->src.val,
-                                          &c->dst.val, 1, ctxt->vcpu))
+                if (!pio_in_emulated(ctxt, ops, c->dst.bytes, c->src.val,
+                                     &c->dst.val))
                         goto done; /* IO is needed */
                 break;
         case 0xee: /* out al,dx */
@@ -2928,8 +2958,14 @@ writeback:
                 string_addr_inc(ctxt, es_base(ctxt), VCPU_REGS_RDI, &c->dst);
 
         if (c->rep_prefix && (c->d & String)) {
+                struct read_cache *rc = &ctxt->decode.io_read;
                 register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
-                if (!(c->regs[VCPU_REGS_RCX] & 0x3ff))
+                /*
+                 * Re-enter guest when pio read ahead buffer is empty or,
+                 * if it is not used, after each 1024 iteration.
+                 */
+                if ((rc->end == 0 && !(c->regs[VCPU_REGS_RCX] & 0x3ff)) ||
+                    (rc->end != 0 && rc->end == rc->pos))
                         ctxt->restart = false;
         }