KVM: x86 emulator: access GPRs on demand
Instead of populating the entire register file, read in registers
as they are accessed, and write back only the modified ones. This
saves a VMREAD and VMWRITE on Intel (for rsp, since it is not usually
used during emulation), and a two 128-byte copies for the registers.
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 42bbf41..e00050c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4313,7 +4313,19 @@
kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx);
}
+static ulong emulator_read_gpr(struct x86_emulate_ctxt *ctxt, unsigned reg)
+{
+ return kvm_register_read(emul_to_vcpu(ctxt), reg);
+}
+
+static void emulator_write_gpr(struct x86_emulate_ctxt *ctxt, unsigned reg, ulong val)
+{
+ kvm_register_write(emul_to_vcpu(ctxt), reg, val);
+}
+
static struct x86_emulate_ops emulate_ops = {
+ .read_gpr = emulator_read_gpr,
+ .write_gpr = emulator_write_gpr,
.read_std = kvm_read_guest_virt_system,
.write_std = kvm_write_guest_virt_system,
.fetch = kvm_fetch_guest_virt,
@@ -4348,14 +4360,6 @@
.get_cpuid = emulator_get_cpuid,
};
-static void cache_all_regs(struct kvm_vcpu *vcpu)
-{
- kvm_register_read(vcpu, VCPU_REGS_RAX);
- kvm_register_read(vcpu, VCPU_REGS_RSP);
- kvm_register_read(vcpu, VCPU_REGS_RIP);
- vcpu->arch.regs_dirty = ~0;
-}
-
static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
{
u32 int_shadow = kvm_x86_ops->get_interrupt_shadow(vcpu, mask);
@@ -4382,12 +4386,10 @@
kvm_queue_exception(vcpu, ctxt->exception.vector);
}
-static void init_decode_cache(struct x86_emulate_ctxt *ctxt,
- const unsigned long *regs)
+static void init_decode_cache(struct x86_emulate_ctxt *ctxt)
{
memset(&ctxt->twobyte, 0,
- (void *)&ctxt->regs - (void *)&ctxt->twobyte);
- memcpy(ctxt->regs, regs, sizeof(ctxt->regs));
+ (void *)&ctxt->_regs - (void *)&ctxt->twobyte);
ctxt->fetch.start = 0;
ctxt->fetch.end = 0;
@@ -4402,14 +4404,6 @@
struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
int cs_db, cs_l;
- /*
- * TODO: fix emulate.c to use guest_read/write_register
- * instead of direct ->regs accesses, can save hundred cycles
- * on Intel for instructions that don't read/change RSP, for
- * for example.
- */
- cache_all_regs(vcpu);
-
kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
ctxt->eflags = kvm_get_rflags(vcpu);
@@ -4421,7 +4415,7 @@
X86EMUL_MODE_PROT16;
ctxt->guest_mode = is_guest_mode(vcpu);
- init_decode_cache(ctxt, vcpu->arch.regs);
+ init_decode_cache(ctxt);
vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
}
@@ -4441,7 +4435,6 @@
return EMULATE_FAIL;
ctxt->eip = ctxt->_eip;
- memcpy(vcpu->arch.regs, ctxt->regs, sizeof ctxt->regs);
kvm_rip_write(vcpu, ctxt->eip);
kvm_set_rflags(vcpu, ctxt->eflags);
@@ -4599,7 +4592,7 @@
changes registers values during IO operation */
if (vcpu->arch.emulate_regs_need_sync_from_vcpu) {
vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
- memcpy(ctxt->regs, vcpu->arch.regs, sizeof ctxt->regs);
+ emulator_invalidate_register_cache(ctxt);
}
restart:
@@ -4637,7 +4630,6 @@
toggle_interruptibility(vcpu, ctxt->interruptibility);
kvm_set_rflags(vcpu, ctxt->eflags);
kvm_make_request(KVM_REQ_EVENT, vcpu);
- memcpy(vcpu->arch.regs, ctxt->regs, sizeof ctxt->regs);
vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
kvm_rip_write(vcpu, ctxt->eip);
} else
@@ -5591,8 +5583,7 @@
* that usually, but some bad designed PV devices (vmware
* backdoor interface) need this to work
*/
- struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
- memcpy(vcpu->arch.regs, ctxt->regs, sizeof ctxt->regs);
+ emulator_writeback_register_cache(&vcpu->arch.emulate_ctxt);
vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
}
regs->rax = kvm_register_read(vcpu, VCPU_REGS_RAX);
@@ -5723,6 +5714,7 @@
{
struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
int ret;
+ unsigned reg;
init_emulate_ctxt(vcpu);
@@ -5732,7 +5724,6 @@
if (ret)
return EMULATE_FAIL;
- memcpy(vcpu->arch.regs, ctxt->regs, sizeof ctxt->regs);
kvm_rip_write(vcpu, ctxt->eip);
kvm_set_rflags(vcpu, ctxt->eflags);
kvm_make_request(KVM_REQ_EVENT, vcpu);