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>

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 7fda16f..b5e12c5 100644 (file)
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -151,6 +151,12 @@ struct fetch_cache {
        unsigned long end;
 };
 
+struct read_cache {
+       u8 data[1024];
+       unsigned long pos;
+       unsigned long end;
+};
+
 struct decode_cache {
        u8 twobyte;
        u8 b;
@@ -178,6 +184,7 @@ struct decode_cache {
        void *modrm_ptr;
        unsigned long modrm_val;
        struct fetch_cache fetch;
+       struct read_cache io_read;
 };
 
 struct x86_emulate_ctxt {

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6de6ad1..ab3fff5 100644 (file)
--- 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;
        }