diff --git a/Makefile b/Makefile
index ac9edba..a9d9e3e 100644
--- a/Makefile
+++ b/Makefile
@@ -122,6 +122,25 @@ endif
 
 QEMU    = qemu-system-x86_64
 
+# Hardware virtualisation, when the host has it.
+#
+# Not a micro-optimisation. Without KVM, QEMU emulates every instruction, and
+# measured on this tree that is where most of "the system feels slow" came from:
+# `ls /bin` took 120 ms emulated against 20 ms with KVM, on identical code. Every
+# guess about the kernel being at fault has to be made against the KVM number,
+# or it is really a measurement of TCG.
+#
+# Probed rather than assumed, because /dev/kvm is absent on a machine without
+# the extension, inside another VM, or when the user is not in the kvm group --
+# and a hard -enable-kvm turns each of those into a QEMU that refuses to start.
+# `-cpu host` only makes sense with KVM: it is the physical CPU, which an
+# emulator cannot present.
+ifneq ($(wildcard /dev/kvm),)
+  QEMU_ACCEL = -enable-kvm -cpu host
+else
+  QEMU_ACCEL = -cpu qemu64,+rdtscp
+endif
+
 # Display for every QEMU target.
 #
 # virtio-gpu is what the display class binds, and what a compositor should be
@@ -463,7 +482,7 @@ ovmf: $(OVMF_CODE) $(OVMF_VARS)
 all: $(OVMF_CODE) $(OVMF_VARS)
 
 qemu-uefi: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
-	$(QEMU) -machine pc-i440fx-9.2 	    -drive if=pflash,format=raw,unit=0,readonly=on,file=$(OVMF_CODE) 	    -drive if=pflash,format=raw,unit=1,file=$(OVMF_VARS) 	    -drive file=fat:rw:$(BUILD)/esp,index=0,media=disk,format=raw 	    -drive file=$(BUILD)/schfs.img,format=raw,index=1,media=disk 	    -m 1G -smp 1 -cpu qemu64,+rdtscp -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT)
+	$(QEMU) -machine pc-i440fx-9.2 	    -drive if=pflash,format=raw,unit=0,readonly=on,file=$(OVMF_CODE) 	    -drive if=pflash,format=raw,unit=1,file=$(OVMF_VARS) 	    -drive file=fat:rw:$(BUILD)/esp,index=0,media=disk,format=raw 	    -drive file=$(BUILD)/schfs.img,format=raw,index=1,media=disk 	    -m 1G -smp 1 $(QEMU_ACCEL) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT)
 
 # Build the ramdisk-root variant. This is a target rather than just
 # "make RAMROOT=1" because toggling RAMROOT changes CFLAGS (-DRAMDISK_ROOT),
@@ -526,7 +545,7 @@ schos.iso: $(BUILD)/kernel/kernel $(BUILD)/uefi/BOOTX64.EFI sysroot-install
 # all, so a kernel that still secretly depends on one fails here rather than
 # in someone's optical drive.
 qemu-iso: schos.iso
-	$(QEMU) -serial mon:stdio $(QEMU_DISPLAY) -cpu qemu64,+rdtscp \
+	$(QEMU) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_ACCEL) \
 	    -cdrom schos.iso -boot d \
 	    -m 1G -smp 2 -machine pc-i440fx-9.2
 
@@ -901,12 +920,16 @@ OVMF_DRIVES = -drive if=pflash,format=raw,unit=0,readonly=on,file=$(OVMF_CODE) \
               -drive file=fat:rw:$(BUILD)/esp,index=0,media=disk,format=raw \
               -drive file=$(BUILD)/schfs.img,format=raw,index=1,media=disk
 
+# Kept as an explicit spelling, but `make qemu` now picks KVM up on its own
+# whenever /dev/kvm exists -- see QEMU_ACCEL. This target differs only in
+# insisting on it, which is what you want when the point is to find out why the
+# host has no /dev/kvm rather than to quietly get a slow machine.
 qemu-kvm: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
 	$(QEMU) -enable-kvm -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) -cpu host \
 	    $(OVMF_DRIVES) -m 1G -smp 2 -machine pc-i440fx-9.2
 
 qemu: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
-	$(QEMU) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) -cpu qemu64,+rdtscp \
+	$(QEMU) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_INPUT) $(QEMU_ACCEL) \
 	    $(OVMF_DRIVES) -m 1G -smp 2 -machine pc-i440fx-9.2
 
 # The root filesystem. Built from the staged sysroot; the kernel mounts it as
@@ -926,7 +949,7 @@ $(BUILD)/schfs.img: $(MKSCHFS) $(BUILD)/sysroot.stamp
 #
 # Once up:  cat /proc/schfs
 qemu-schfs: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
-	$(QEMU) -serial mon:stdio $(QEMU_DISPLAY) -cpu qemu64,+rdtscp \
+	$(QEMU) -serial mon:stdio $(QEMU_DISPLAY) $(QEMU_ACCEL) \
 	    $(OVMF_DRIVES) -m 1G -smp 2 -machine pc-i440fx-9.2
 
 # -----------------------------------------------------------------------